Term
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Definition
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Term
| What is Electromagnetic compatibility? |
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Definition
| The ability of a device, equipment, or system to operate properly in its intended electromagnetic environment without introducing significant electromagnetic interference (EMI) into the environment. 2-1 |
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Term
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Definition
| The transfer of electromagnetic energy from one device or system to another device or system operating in the same environment that causes interference with the normal operation of devices or systems. 2-1 |
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Term
| When does the potential for EMI increase? |
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Definition
| When devices or systems share a common electromagnetic environment and their frequencies of operation overlap. 2-1 |
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Term
| What happens if devices share spaces but operate over a different range of the electromagnetic spectrum? |
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Definition
| Lower levels of EMI are to be expected. 2-1 |
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Term
| What causes coupling between two circuits or systems? |
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Definition
One or more of the following:
Conductive coupling (i.e., when a common alternating (ac) branch circuit is shared between two devices).
Inductive coupling (by magnetic fields)
Capacitive coupling (by electrical fields)
Electromagnetic coupling ( by radiated waves). 2-1 |
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Term
| What are the three essential elements of an EMI event? |
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Definition
The source of the EMI or electromagnetic energy transfer between an interfering source and a susceptible device or system.
The susceptible device or system that cannot perform as designed, configured, or programmed due to the EMI event.
A coupling path that promotes the disturbance between the interfering source and the susceptible device or system. 2-1 |
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Term
| How are EMI problems mitigated? |
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Definition
| By identifying the source, the susceptible device and eliminating the path between the two. 2-1 |
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Term
| What does the electromagnetic spectrum include? |
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Definition
Light
Radio waves
Microwaves
Infrared radiation (IR)
Ultraviolet rays
X-rays
Gamma rays. 2-2 |
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Term
| How are electromagnetic waves distinguished? |
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Definition
| By their wavelength, which is expressed in meters (m), or frequency, which is expressed in hertz (Hz) |
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Term
| Conducted coupling may affect electronic devices primarily through what three paths? |
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Definition
Input signal lines
Output signal lines
Utility or premises electrical power distribution. 2-3 |
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Term
| Radiated interference enters electronic devices primarily by means of what four things? |
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Definition
Proximity to interfering sources
Missing or inadequate gaskets/enclosures
Missing or inadequate bonding and grounding (earthing) system components
missing or inadequate device or cable shielding. 2-3 |
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Term
| Precautions should be taken by the ITS designer involving the interaction and interdependence among which components? |
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Definition
AC or DC power distribution
Bonding and grounding system components
Transient voltage surge protection on ac electrical and ITS signal paths.
Cabling
Shields
Filtering
Interface design. 2-4 |
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Term
| Do electrical codes provide guidance for EMC? |
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Definition
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Term
| Commercial building bonding and grounding standards focus on the infrastructure of a building and often do not cover: |
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Definition
Tolerances related to surge current immunity and component insulation to withstand electromagnetic disturbance and surge voltages and currents.
The specific methods for radio frequency interference/electromagnetic interference (RFI/EMI) mitigation for equipment or systems. 2-4 |
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Term
| What should the ITS designer consider in relation to EMI, before choosing the type of cabling required to support the application using the cabling? |
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Definition
| The MICE classification of the environment where the cabling will be deployed. 2-4 |
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Term
| What is an electromagnetic field? |
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Definition
| A combination of an electrical field( created by stationary charges) and magnetic field (created by electrical currents). 2-5 |
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Term
| What does a magnetic field do? |
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Definition
| induces a voltage on a current-carrying conductor, and is produced around a current-carrying conductor when a current is present. 2-5 |
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Term
| What does an electrical field do? |
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Definition
| induces a current on a conductor placed in its proximity. 2-5 |
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Term
| Why can electromagnetic fields be either desirable or undesirable? |
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Definition
| depending on whether the electromagnetic fields interfere with the operation of the network or electronic devices. 2-5 |
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Term
| What are electromagnetic fields that have undesirable effects on a device, equipment, or system referred to as? |
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Definition
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Term
| External EMI sources are typically: |
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Definition
Radio transmitters/receivers
electrical power lines
Radar
Cellular phones
Engine ignitions
Lightning
Electrostatic discharge (ESD) when responsible for coupling noise into circuits and systems.
Electric motors
Electronic ballasts. 2-5 |
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Term
| Is control of external EMI sources practical? |
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Definition
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Term
| Internal EMI sources are typically: |
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Definition
Electrical power supplies
electrical power cables
Rectifiers
Oscillators
Digital clocks
Digital signal processors
Common-mode signaling
Long term or short term variations in ac voltage
Unbalance of current between ac circuit conductors
Power signaling systems
power conditioners. 2-6 |
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Term
| why are unshielded and un twisted conductors susceptible to external unwanted signal emissions? |
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Definition
| Because they act as antennas. 2-6 |
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Term
| what does the amount of radiation or coupling depend on? |
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Definition
| the level of common-mode voltage at the output of the transmitter. Also for unshielded balanced twisted pair circuits, the amount of radiation or coupling depends on the level of differential-to-common-mode signal conversion. 2-6 |
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Term
| What causes differential-to-common-mode signal conversion? |
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Definition
| Asymmetrical twisted-pair geometry, unbalanced connector designs, or excessive untwisting at cable terminations. 2-6 |
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Term
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Definition
| The electromagnetic energy created by equipment. 2-8 |
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Term
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Definition
| Equipment's ability to withstand electromagnetic disturbances. 2-8 |
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Term
| How are radiated emissions determined? |
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Definition
| by measuring the electric and magnetic field strength of the outgoing radiation. 2-8 |
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Term
| What is the unit of measure for the electrical field strength? |
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Definition
| volt per meter (V/m), millivolts per meter (mV/m), or microvolts per meter (uV/m). 2-8 |
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Term
| What is the unit of measure for the magnetic field strength? |
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Definition
| ampere per meter (A/m). 2-8 |
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Term
| What determines if a piece of equipment is electromagnetically compatible relative to emissions and/or conductive standards? |
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Definition
| The magnetic and electric fields are measured and if they are below specified limits, they are electromagnetically compatible. 2-8 |
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Term
| How is immunity to radiated emissions determined? |
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Definition
| By exposing the device being measured to a specific electromagnetic field and monitoring its performance. If there is no undesirable response from the device, it is electromagnetically compatible relative to immunity. 2-8 |
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Term
| At what distances are radiated interference limit measurements taken by means of resonant dipoles? |
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Definition
| 3 meters (10ft) for FCC class B, and 10meters (33ft) for FCC class A. 2-8 |
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Term
| What are some methods and apparatus' used for measurements of radiated and conducted interference? |
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Definition
Open area test site (OATS)
Radiated interference measurements:
-Anechoic chamber
-Transverse electromagnetic (TEM)cell
-Reverberating chamber
Conducted interference measurements:
-Common-mode and differential-mode interferences
-Conducted electromagnetic noise on power supply lines
-Conducted EMI from equipment. 2-9 |
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Term
| A significant part of accomplishing EMC depends on the what considerations? |
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Definition
All EMI problems are explainable by the basic laws of physics.
The real task involves narrowing a spectrum of possible EMI and EMC combinations down to a few.
Even with good design and installation, EMI can occur as an exception to the rule. EM often involves "hidden" schematics or "stray" paths.
EMI is often easy to remedy once the root cause is identified.
EMI is a by-product of technology advancement.
Accomplishing EMC often involves designing for threats that may or may not materialize. It is possible for EMC methods to function well in one location, and fail in another. 2-15 |
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Term
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Definition
| Their immunity capability. 2-15 |
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Term
| What conducted and radiated sources do EMI problems typically come from? |
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Definition
Communications
Transmitters
Radar
Telemetry
Navigation
Motors
Switches
Electrical power lines. 2-16 |
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Term
| What transfer and propagation sources do EMI problems typically come from? |
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Definition
Space separation
Shielding failures
Poor filtering
Improper grounding
Electrical power lines
Input/output cabling. 2-16 |
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Term
| What receiving or receptor elements do EMI problems typically come from? |
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Definition
Receivers (all types)
Sensitive electronic components
Relay equipment
biological hazards (E.G, human). 2-16 |
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Term
| What are two natural sources of EMI? |
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Definition
Atmospheric electricity
Cosmic radiation / geomagnetism disturbances. 2-16 |
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Term
| Man made sources of EMI in electrical power include: |
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Definition
Conversion (step up/ step down)
Distribution (i.e., insulators, cabling, transformers, or grounding)
Generators. 2-16 |
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Term
| Man made sources of EMI in communications electronics include: |
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Definition
Broadcast AM/FM, VHF, UHF bands
Communications fax, telegraphy, maritime, telephone, or radio control
Mobile telephone communications
Personal communications system (PCS)
Navigation aircraft beacons
Radar search. 2-17 |
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Term
| Man made sources of EMI in relay communications include: |
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Definition
Ionospheric scatter microwave
Satellite relay
Tropospheric scatter. 2-17 |
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Term
| Man made sources of EMI in tools and machines include: |
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Definition
telecommunications electronic equipment
Information technology equipment
Appliances
Industrial machines
Office equipment
Power tools
material-moving equipment. 2-17 |
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Term
| Man made sources of EMI in ignition systems include: |
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Definition
Engines
Tools
Vehicles. 2-17 |
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Term
| Man made sources of EMI in Industrial and consumer equipment or products include: |
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Definition
Heaters
Industrial controls and computers
Fluorescent lights
Medical equipment
Ultrasonic devices
Welders
Dimmers
electronic ballasts. 2-17 |
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Term
| Copper cables attached to what equipment can cause EMI? |
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Definition
Electrical power supplies
Radio and TV receivers
Computer room air conditioner (CRAC) units, UPS's
Computing devices (i.e., computers, servers ,routers, switches, keyboard,/video/mouse (KVM)
Telecommunications and data equipment. 2-18 |
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Term
| What are some methods used to suppress or prevent unwanted signals? |
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Definition
Shielding
Filtering
bonding and grounding. 2-18 |
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Term
| Improper shielding, filtering, and grounding can increase what? |
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Definition
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Term
| For balanced twisted-pair systems that uses a balanced signal (e.g., differential mode), it is important to ensure the cabling elements are well balanced and the pairs are not excessively untwisted to reduce what? |
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Definition
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Term
| Define Electrostatic discharge (ESD) |
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Definition
| A natural phenomenon in which accumulated electrical charges are discharged. |
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Term
| When is static electricity created? |
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Definition
| When two materials of different dielectric constants rub against each other. 2-19 |
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Term
| What are the three distinguished types of ESD? |
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Definition
Discharge through spark in the air
Radiated effects of ESD
Contact discharge |
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Term
| What should be done by the ITS designer to reduce ESD? |
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Definition
| Provide a grounding point in all equipment locations so that personnel can use an approved method of discharging the build up of static charge both before and during the handling of electronic components. 2-19 |
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Term
| How many levels of immunity are there for air and static discharges? |
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Definition
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Term
| How can Transmission lines or transmission channels be described? |
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Definition
| In terms of distributed network parameters (i.e., resistance, inductance, conductance, and capacitance) per unit length. 2-22 |
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Term
| Generally what can represent the wireline channel? |
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Definition
| The series resistance and inductance per unit length along with the shunt capacitance and conductance per unit length. A model (designated model) T is used to represent this. 2-22 |
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Term
| Usually the dielectric surrounding the conductor used to separate the two conductors in the same cable pair has what? |
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Definition
| Very good frequency response, so the conductance can be considered negligible. 2-22 |
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Term
| For what frequency range can the value of the conductance be assumed to be zero? |
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Definition
| From 1Mhz to 600Mhz. 2-22 |
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Term
| What must be done with a T model in order to represent a complete transmission channel? |
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Definition
| A number of T sections (short cable length) have to be connected in cascade. 2-23 |
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Term
| What is responsible for the energy storage in cable? |
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Definition
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Term
| How can cable capacitance be computed? |
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Definition
| By the suitable summation of several T sections connected in cascade to model a long wire channel. 2-23 |
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Term
| How is capacitance of a cable pair affected by its length? |
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Definition
| The capacitance will increase as the length increases, and will decrease as the length decreases. 2-23 |
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Term
| What is capacitance of telecommunications cables also called? |
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Definition
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Term
| What happens to mutual capacitance as the category of the cable increases? |
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Definition
| The mutual capacitance decreases. 2-24 |
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Term
| What should be verified on equipment to ensure immunity to radiated fields? |
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Definition
| Proper testing or certification within a wide frequency range. 2-25 |
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Term
| What can happen to both shielded and unshielded cables, especially at the lower frequencies, if they aren't properly installed? |
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Definition
| The cabling attached to a system could act as an effective antenna and cause problems. 2-25 |
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Term
| When are electrical fast transient (EFT) disturbances created? |
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Definition
| When inductive and capacitive circuits are switched on and off over an operation cycle. 2-25 |
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Term
| What are transient disturbances? |
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Definition
| Often referred to as electrical surges, they are short duration current, voltage, or power on low-voltage electrical power lines. 2-26 |
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Term
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Definition
| Radio Frequency Interference, a form of EMI, can be defined as the degradation of a desired signal at the receptor-end caused by radio frequency disturbance, which has components in the radio frequency range. 2-27 |
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Term
| What is usually the only way to mitigate effects of RFI on telephone sets and other equipment? |
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Definition
| The deployment of shielded or screened cabling in the concerned areas. 2-27 |
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Term
| Copper conductors and their sheaths may act like an antenna under certain conditions and do what? |
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Definition
| Pick up interference from radio stations in their proximity thus coupling undesired signals on telephone sets and other equipment connected to them. 2-27 |
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Term
| What can affect a given telephone set's ability to function in the presence of radio signals? |
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Definition
| The buildings cabling practices and effective bonding and grounding. 2-27 |
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Term
| What are the two different types of unwanted signals on cable in an EMI event? |
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Definition
Common-mode
Differential mode. 2-28 |
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Term
| Which signal interference usually predominates? |
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Definition
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Term
| How does common-mode signals interfere? |
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Definition
| Cm interference due to a radiation source induces a common-mode voltage (or noise) in the loop formed between the victim circuit and the ground plane. 2-28 |
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Term
| How does a differential-mode signal interfere? |
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Definition
| DM signals are coupled into a pair of conductors due to radiation from an EMI source. DM noise can also be a result of a coupling between a given conductor and its return path. 2-28 |
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Term
| Is the ground plane involved in differential-mode coupling? |
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Definition
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Term
| What is preferred to successfully filter both types of unwanted signals? |
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Definition
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Term
| How is common-mode interference reduced? |
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Definition
| When afflicted lines are coupled together through a ferrite bead. 2-28 |
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Term
| How is differential-mode interference reduced? |
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Definition
| Individual ferrite beads can be installed on each input lead of the victim line or output lead of the interfering circuit or line. 2-28 |
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Term
| What two ways can common-mode signal affect equipment? |
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Definition
It can directly affect equipment operation (e.g., locking up a computer).
The CM signal can be converted to a DM signal by the cable or equipment. 2-28 |
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Term
| What reduces the conversion of CM interference to DM interference? |
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Definition
| The better balanced a circuit is, the less CM to DM conversion occurs. 2-28 |
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Term
| What is the critical parameter in CM to DM conversion? |
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Definition
| Pair balance, or alternatively CM rejection ratio. 2-28 |
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Term
| What does control of CM to DM conversion help mitigate? |
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Definition
| The effects of EMI in a given circuit or system. 2-28 |
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Term
| From a susceptibility standpoint, where can a CM voltage be converted into a DM voltage? |
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Definition
| At the input of the disturbed circuit. 2-28 |
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Term
| From an emission standpoint what does a DM voltage transmitted over a given circuit generate? |
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Definition
| CM voltages and currents along the ground loop through a ground path. 2-28 |
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Term
| When does CM unwanted signal become evident within an electronic system? |
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Definition
| Only when it is measured against the reference ground. 2-28 |
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Term
| How does DM noise affect equipment? |
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Definition
| Primarily by corrupting transmitted signals on a balanced circuit. 2-29 |
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Term
| What are some sources of unwanted signals? |
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Definition
Electrical Power convertors
Logic circuits
Electrical power lines
Cabling |
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Term
| What is generally the longest path between circuit components and modules? |
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Definition
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Term
| What is the effect of unwanted signals as a result of EMI on telecommunications cabling systems? |
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Definition
| The degradation of the transmission channel leading the system to communications errors. The effects of this interference may be represented by bit error rate (BER). 2-30 |
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Term
| In relation to EMI the higher the transmission rate: |
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Definition
| The higher the effect of the interference. 2-30 |
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Term
| What does proper grounding and bonding do to EMI? |
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Definition
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Term
| What are important items when designing a cabling system for EMC? |
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Definition
Availability of structural steel within the building
Bonding infrastructure for entrance facilities (Efs), equipment rooms (Ers), and Telecommunication rooms (TRs)
Ac grounding electrode system design
Ac equipment grounding system design
Use of surge protection
Use of shielded cable
Existing CM or DM disturbance levels
Existing or possible sources of EMI. 2-31 |
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Term
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Definition
| Two parallel paths that have identical conductive terminations to two separate grounding references. Often, but not always, the earth is one of the parallel paths between grounding references. 2-31 |
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Term
| When can ground loops be a source of EMI? |
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Definition
| When shielded cabling systems where the earth or inadequately bonded grounding references cause a CM voltage to develop between the two grounding references. 2-31 |
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Term
| What is the necessary step to take when a ground loop is present? |
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Definition
| It is necessary to provide some kind of grounding (earthing) systems discrimination or electrical insulation against the ground loop path. 2-31 |
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Term
| When can a cable shield only be grounded on one end and still provide effective resistance to the effects of EMI? |
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Definition
| At low frequencies, up to about 1MHz. 2-32 |
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Term
| At what frequencies is it recommended to ground both ends of a cable shield to guarantee minimum potential differences between both ground connections and shield against ground loop caused EMI? |
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Definition
| Higher frequencies, above 1 MHz. 2-32 |
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Term
| What is the standard for bonding and grounding? |
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Definition
ANSI-J-STD-607A
IEC 60364-4-43. 2-32 |
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Term
| What is the standard requirement for the maximum difference in ground potential between two ends of a cable? |
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Definition
| 1V room mean square (rms). 2-32 |
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Term
| At higher frequencies what factor helps complete the ground loop when the cable shield is grounded at one cable end only? |
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Definition
| There is stray capacitive coupling that tends to complete the ground loop. 2-33 |
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Term
| Can the grounding components that are established for the ac electrical distribution be an additional source of EMI? |
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Definition
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Term
| Due to the finite ground plane conductivity, what is created by stray ground current through common mode impedance between two ground points? |
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Definition
| It creates coupled interference between two circuits or systems. 2-34 |
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Term
| What does the equipment-grounding conductor contained within power circuits provide for the connected telecommunications equipment? |
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Definition
| An additional grounding (earthing) reference. 2-34 |
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Term
| What are two mechanisms for unwanted signal coupling? |
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Definition
Induced unwanted signal due to external electromagnetic field coupling
Conducted unwanted signal due to external ground loops. 2-35 |
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Term
| Is induced or conducted unwanted signal more important in creating common mode voltage? |
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Definition
| Both are equally important. 2-35 |
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Term
| what is a function of the electrical field strength (E) and the loop area formed by a conductor of length that is suspended at an average height above the ground plane? |
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Definition
| Induced common mode (CM) coupling voltage. 2-35 |
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Term
| What can installing the cable close to the ground effect the magnitude of induced CM unwanted signal coupling? |
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Definition
| Changing the average height from 1m to 100mm reduces the unwanted signal coupling by a factor of 10. 2-36 |
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Term
| Which pathway type is desirable for controlling EMI? |
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Definition
|
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Term
| what should be done to metallic raceways and enclosures to ensure proper grounding of all metallic parts and units to minimize the accumulation of voltages? |
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Definition
| they should be made electrically continuous. 2-36 |
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Term
| How do metallic raceways reduce EMI? |
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Definition
They reduce common mode field to loop EMI pickup as well as emissions at frequencies from 50Hz to 100MHz.
They reduce common mode crosstalk by increasing wire to ground capacitances
They also create a reference ground plane. 2-36 |
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Term
| What does connecting the raceway directly to the equipment structure or chassis by means of a jumper accomplish? |
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Definition
| Such practices contribute to the reduction of susceptibility and problems due to CM voltage in large sites. 2-37 |
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Term
| Generally, how many ends of instrumentation cables should be grounded? |
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Definition
| One end. However for long runs and interfaculty runs, both ends should be grounded. 2-38 |
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Term
| What is electromagnetic shielding? |
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Definition
| A technique employed to reduce or prevent coupling of undesired radiated electromagnetic energy into a given system to enable it to properly operate in its electromagnetic environment. It can also be used to minimize the level of radiation from this given system into its environment. 2-38 |
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Term
| In what frequency range is electromagnetic shielding effective? |
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Definition
| Electromagnetic shielding is effective in several degrees over a large part of the electromagnetic spectrum from low frequency and dc to the much higher microwave frequencies. 2-38 |
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Term
| For low frequency noise mitigation, what is the major mitigation technique? |
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Definition
| cable twists absorb the major part of the EMI effects. 2-38 |
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Term
| For high frequency noise mitigation, what is the major mitigation technique? |
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Definition
| At high frequencies cable shields absorb the electromagnetic waves. 2-28 |
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Term
|
Definition
| The amplitude of a wave decreases as it passes through a medium. |
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Term
| Why does absorption loss occur? |
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Definition
| Because currents induced in the medium are attenuated and produce heating of the material. 2-39 |
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Term
| How is cable shielding effectiveness measured? |
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Definition
| Shield transfer impedance. 2-29 |
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Term
| What is transfer impedance? |
|
Definition
| a measure of the voltage induced on the inside surface of a shield for a current flowing on the outside of the shield.2-39 |
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Term
| What are the two main differences concerning unwanted signal coupling (EMI) between UTP and ScTP or FTP? |
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Definition
ScTP and FTP cables also consider:
The effectiveness of the cable shield to reduce external unwanted signal
How the cable shield is terminated at the equipment. 2-39 |
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Term
| What determines shield effectiveness? |
|
Definition
Operating frequency
Type, thickness, and geometry of the shielding materials
Type and quality of shield terminations
Method of grounding (earthing) the shield. 2-39 |
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Term
| Can shield discontinuities adversely affect the shielding effectiveness? |
|
Definition
|
|
Term
| Does the grounding (earthing) of cable screens affect the EMC cable performance? |
|
Definition
|
|
Term
| What must be done at the terminating of shielded/screened cables into connectors to provide good EMC? |
|
Definition
| A good connection must be made between the cable shield and the connector metallic body (or gasket). 2-39 |
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Term
| What technique must be employed when grounding cable shields? |
|
Definition
| A 360 degree connection must be made avoiding breeches in the conductor continuity. 2-39 |
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Term
| What type of cable should an ITS designer select in regards to EMI? |
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Definition
| a cable designed to keep the interference level below the regulatory limits. 2-40 |
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Term
| Where are telecommunications systems to be placed in regards to equipment that generates EMI. |
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Definition
| Telecommunications systems should not be near EMI generating equipment. 2-40 |
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Term
| What are typical EMI sources in horizontal pathways? |
|
Definition
Electric motors
transformers
Fluorescent lighting
Copiers
electric power cables. 2-40 |
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Term
| What should be done to avoid EMI in horizontal pathways? |
|
Definition
| Maintaining physical separation between possible sources and the telecommunications cabling. 2--40 |
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Term
| Is EMI an important consideration when designing pathways and spaces? |
|
Definition
|
|
Term
| What precautions should be taken when designing pathways and spaces in regard to EMI? |
|
Definition
Use grounded metallic pathways to limit inductive unwanted signal coupling between the telecommunications cabling and potential sources of EMI
Use sheathed cables or other branch circuit cable constructions (e.g., taped, twisted, or bundled) that prevents separation of the line, neutral, and grounding conductors to minimize EMI emission form the electrical power conductors. 2-41 |
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Term
| The use of what item in branch circuits can limit the propagation of electrical surges and associated hardware? |
|
Definition
|
|
Term
| Under the general guidelines for increased protection against EMC what do higher balanced twisted pair cable categories result in? |
|
Definition
| Better noise rejection response. 2-42 |
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Term
| Under the general guidelines for increased protection against EMC what should multiple conductor cables consist of? |
|
Definition
|
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Term
| Under the general guidelines for increased protection against EMC what should multiple conductor cables used for transmission of several individual signals consist of? |
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Definition
| balanced twisted-pair conductors with different twists. 2-42 |
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Term
| Under the general guidelines for increased protection against EMC what should multiple conductor cables should have what? |
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Definition
| An overall shield to further improve EMC. 2-42 |
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Term
| Under the general guidelines for increased protection against EMC what should be done with unused conductors? |
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Definition
| They should be terminated or removed altogether. 2-42 |
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Term
| Under the general guidelines for increased protection against EMC what should be done with similar-type signals? |
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Definition
| Similar-type signals should be run together, and not intermixed (e.g., analog voice with analog voice, and data with data). 2-42 |
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Term
| Under the general guidelines for increased protection against EMC where should low-level data transmission lines be run in relation to high-level electrical power lines? |
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Definition
| They should not be run parallel. 2-42 |
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Term
| Under the general guidelines for increased protection against EMC what should be done when signal lines are found close to switchgear? |
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Definition
| Use localized magnetic barriers. 2-42 |
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Term
| Under the general guidelines for increased protection against EMC where should cables be installed in relation to buried high-voltage transmission lines or areas subject to high-ground currents? |
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Definition
| Cable should not be buried below or parallel to high transmission lines or in areas subject to high-ground currents. 2-42 |
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Term
| Under the general guidelines for increased protection against EMC where different cable conditions must cross? |
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Definition
| The crossing should be at a 90 degree angle. 2-42 |
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Term
| Under the general guidelines for increased protection against EMC what should be considered in designing tray and conduit paths? |
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Definition
| Tray and conduit separation spacing should be considered a potential problem area when designing and maintaining a telecommunications cabling system. 2-42 |
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Term
| Under the general guidelines for increased protection against EMC What is the recommendation for dealing with source suppression? |
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Definition
| Source suppression should be considered, as dealing with unwanted signal at the source helps eliminate major corrective action on cabling systems. 2-42 |
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Term
Under the general guidelines for increased protection against EMC
electrical-power circuits, including premise feeder cables that serve telecommunication systems: |
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Definition
| Should be encased in metal conduit. 2-42 |
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Term
Under the general guidelines for increased protection against EMC
each branch circuit: |
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Definition
| Should be in a separate conduit or be implemented with shielded cables. 2-42 |
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Term
Under the general guidelines for increased protection against EMC
What protection should be provided to metallic telecommunications circuits in critical areas? |
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Definition
| They should be installed in metallic conduit, and shielded cables are preferred. 2-42 |
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Term
Under the general guidelines for increased protection against EMC
are signal conductors allowed to be installed with power conductors? |
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Definition
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Term
Under the general guidelines for increased protection against EMC
what should be done to keep potential EMI sources away from susceptible telecommunications equipment? |
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Definition
| Maintain adequate physical separation per defined guidelines. 2-42 |
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Term
Under the general guidelines for increased protection against EMC
what should be done to reduce transients that emanate from inductive devices that are being switched off? |
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Definition
| Use surge-protection devices, and locate them as close as possible to the source of the transient. 2-43 |
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Term
Under the general guidelines for increased protection against EMC
reducing EMI from fluorescent lamps located inside of an enclosure consists of what precautions? |
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Definition
Place a shielding grid over the lamp
Install shielded cable between the lamp and the electrical power switch
Install a metal enclosed electrical power strip
Place a filter between the electrical power switch and the electrical power line
Shield the electrical power line. 2-43 |
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Term
Under the general guidelines for increased protection against EMC
conduits and enclosures should be what? |
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Definition
| continuously grounded, which helps to reduce emission and reception of EMI. 2-43 |
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Term
Under the general guidelines for increased protection against EMC
what should be done in regards to radiating antenna and towers? |
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Definition
| Minimize the proximity to these sources. Electric field strength can overwhelm sensitive receivers. 2-43 |
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Term
| What effect does EMI have on optical fiber? |
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Definition
| None, Optical fiber is immune to EMI. 2-43 |
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Term
| What's the minimum separation distance required between Unshielded power lines or electrical equipment in proximity to open or nonmetal pathways? |
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Definition
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Term
| What's the minimum separation distance required between Unshielded power lines or electrical equipment in proximity to a grounded metal conduit pathway? |
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Definition
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Term
| What's the minimum separation distance required between Power lines enclosed in a grounded metal conduit in proximity to a grounded metal conduit pathway? |
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Definition
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Term
| What's the minimum separation distance required between Electrical motors and transformers? |
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Definition
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Term
| What's the minimum separation distance between metallic cabling and Fluorescent lamps? |
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Definition
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Term
| What's the minimum separation distance between metallic cabling and Neon lamps? |
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Definition
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Term
| What's the minimum separation distance between metallic cabling and Mercury Vapor Lamps? |
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Definition
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Term
| What's the minimum separation distance between metallic cabling and High-intensity discharge lamps? |
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Definition
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Term
| What's the minimum separation distance between metallic cabling and arc welders? |
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Definition
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Term
| What's the minimum separation distance between metallic cabling and Frequency induction heating? |
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Definition
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Term
| What should be done when product suppliers guarantees do not exist |
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Definition
| Analysis shall be performed regarding possible disturbances. 2-44 |
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Term
| Where are power line EMI filters mandatory? |
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Definition
| In all modern electronics (active equipment). 2-45 |
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Term
| What will a good EMI filter do? |
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Definition
| Reduce radiated interference coming in or out through the power line cord, and filters are useful every time a switching power supply is used. 2-45 |
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Term
| What are power line filters designed to do? |
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Definition
| Mitigate EMIs in the line for both CM and DM disturbances, |
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Term
| What must a successful power line EMI filtering scheme provide? |
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Definition
Maintenance of signal integrity
Effective attenuation of high-frequency unwanted signals, as well as broadband CM unwanted signal. 2-46 |
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Term
| Isolation transformers provide isolation over what? |
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Definition
| A wide frequency range. 2-46 |
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Term
| Where are isolation transformers implemented? |
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Definition
| In the circuit level of data communications equipment. 2-46 |
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Term
| What are the primary function of isolation transformers? |
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Definition
| To interrupt the CM ground loop at the receiver or transmitter end. 2-46 |
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Term
| What transfer is referred to as mode conversion? |
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Definition
| When CM voltage is transferred to the secondary of the transformers as DM noise. 2-46 |
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Term
| What are isolation transformers commonly used for? |
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Definition
| LAN and other digital communication applications. 2-46 |
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Term
| Ferrite toroids beads and sleeves are used as what? |
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Definition
| Very efficient components to mitigate EMI problems. 2-47 |
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Term
| How do DM and CM ferrite toroids differ? |
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Definition
| DM ferrite toroids are wrapped around each wire, whereas CM ferrite toroids are wrapped around a whole bundle of cables. 2-47 |
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Term
| When are ferrites typically used? |
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Definition
| When the alternative cable sheath grounding is not efficient enough for opening the ground loop due to high-frequency interference. They are also indicated when the cable shield currents need to be reduced without shield interruption. 2-47 |
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Term
| Where are ferrites installed to mitigate emission problems? |
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Definition
| The ferrite shall be installed at the source cable end. 2-47 |
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Term
| Where are ferrites installed to mitigate susceptibility issues? |
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Definition
| The ferrite shall be installed at the input to the susceptible unit. 2-47 |
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Term
| What must be avoided when using split type ferrites? |
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Definition
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Term
| What level of reduction in the electrical power of the interfering signals can make a dramatic difference? |
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Definition
| A level of reduction as little as 10 times. 2-48 |
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Term
| How are level reductions in the electrical power of interfering signals reduced? |
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Definition
| The reduction is routinely accomplished by careful applications of shielding materials, or by the use of a prefabricated room. 2-48 |
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Term
| What does the concept of balance refer to in a balanced twisted pair cable? |
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Definition
| The unwanted signal currents flowing in each conductor of a pair are equal in magnitude, and flow in the same direction 2-49 |
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Term
| What can be done in a balanced twisted pair system to further improve CM rejection? |
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Definition
| Add a CM choke. A minimum common mode rejection ratio (CMRR) of 40 dB is desirable. 2-49 |
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Term
| In practice cables and connecting hardware in a balanced system exhibit a finite unbalance in what? |
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Definition
| Capacitance, resistance, and inductance between each conductor and the ground return path. 2-50 |
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Term
| What happens to part of the CM unwanted signal in a balanced system due to finite unbalance? |
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Definition
| Part of the unwanted signal is converted to DM unwanted signal that passes directly to the input of the receiver. 2-50 |
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Term
| What is a measure of the conversion from CM to DM unwanted signal due to cabling unbalance? |
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Definition
| Longitudinal conversion transfer loss (LCTL) measured in dB. 2-50 |
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Term
| What are the three major components of EMI relating to telephone transmission facilities placed in a joint-use utility tunnel with an electrical power system? |
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Definition
Induced electromagnetic fields from the electrical power system.
Coupling between the electrical power and the telecommunications systems.
The susceptibility of the telecommunications system. 2-51 |
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Term
| The magnitude of the electrical power line influence is determined by the: |
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Definition
magnitude of the current that propagates over the power cable.
Physical configuration of the line. 2-51 |
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Term
| What problems do voltages induced into telephone plant pose? |
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Definition
| They can create personnel safety hazards and service problems, especially for equipment designed to operate at low signal levels. 2-51 |
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Term
| What methods help minimize electrical power systems influence on telephone plant in joint use tunnels? |
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Definition
| using well-balanced, three phase systems, and filters to reduce harmonics. 2-51 |
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Term
| What four parameters determine the level of coupling from mutual capacitance/ mutual inductance between the electrical power and the telecommunications facility? |
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Definition
Physical separation between the power and the telecommunications facilities.
Length of exposure of cables running parallel throughout their pathways.
Impedance of the return path for the unbalanced circuit (e.g., CM return, ground loop).
Shielding effectiveness of the electrical power and telecommunications cables. 2-51 |
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Term
| What is considered good practice in order to obtain a better response in terms of an overall system's EMI? |
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Definition
| It is good practice to use balanced shielded cables properly grounded at both ends for connection between two circuits, or systems. 2-53 |
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Term
| Why are metal components at both ends of a cable grounded? |
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Definition
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Term
| Why do cable shields need to be grounded at both ends? |
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Definition
| So that the shield currents can counteract the effects of electromagnetic unwanted signal induction from an external field. 2-53 |
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Term
| What is an unfortunate occurrence that can be created by grounding the shield at both ends of a cable? |
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Definition
| It creates the possibility of conducted unwanted signal due to ground loop currents. 2-53 |
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Term
| What is recommended due to the instability of the stray capacitance value along a wide frequency range? |
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Definition
| It is recommended to ground shielded cabling systems at both cable ends. 2-54 |
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Term
| What two characteristics of the telecommunications circuit determines susceptibility? |
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Definition
The amount or presence of shielding provided by the cable sheath, or by other grounded conductors.
The balance of the telecommunications circuit. 2-55 |
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Term
| What are the worst creators of unwanted signals? |
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Definition
| High-frequency transients generated by starting and stopping machinery (air compressors, elevator/lift motors) or from switching (power supplies, UPS units). 2-55 |
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Term
| What is a common solution to limit unwanted signal currents? |
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Definition
| To remove grounds at various points, which is not recommended because it defeats the purpose of using a shielded cable. 2-55 |
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Term
| In order to avoid problems what should the difference in potential between two grounds be at? |
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Definition
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Term
| What is the recommended Longitudinal Balance (immunity)? |
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Definition
| It is recommended to use an overall balance of 60dB at low frequencies and 30dB to 40dB or greater at high frequencies. 2-55 |
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