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DB > TDMM Chapter 8 > Flashcards

TDMM Chapter 8 Flashcards

1
Q

ac

A

Alternating Current
A current flow that alternates periodically (usually sinusoidal) in magnitude and direction

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2
Q

BBC

A

Backbone Bonding Conductor
A conductor that is intended to equalize potentials between TRs on the same floor of a structure where multiple TBBs are used in a multi story building

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3
Q

Bonding

A

The connection intended to safely and effectively equalize the potential differences between two metallic items

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4
Q

dc

A

Direct Current
Current flow that has a constant direction. The letters dc are also used generically to refer to any constant waveform.

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5
Q

EMC

A

Electromagnetic Compatibility
The ability of equipment to function in a manner that makes them immune to certain amounts of electromagnetic interference (EMC) while keeping the interference generated within specific limits

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6
Q

EMI

A

Electromagnetic Interference
Radiated of conducted electromagnetic energy that has an undesirable effect on electronic equipment or signal transmissions

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7
Q

GEC

A

Grounding Earthing Conductor
The conductor used to connect to grounding (earthing) electrode to either the equipment grounding conductor or grounded conductor of the circuit at the service equioment

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8
Q

GPR

A

Ground Potential Rise
A voltage difference between a grounding electrode system and the earth return currents produced by a lighting strike or a power fault current

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9
Q

Grounding

A

The establishment of a reference for the electrical power source, the electrical equipment or both

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10
Q

IG

A

Isolated Ground
An equipment grounding topology that presumably reduces the effects of EMI or RFI on the equipment grounding system

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11
Q

Impedance

A

The total opposition of electrical current in ac circuits or an ac waveform up a dc or ac circuit or conductor

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12
Q

Lightning Exposure

A

An outdoor telecom cables susceptibility to electrical power system faults or to lighting or other transients

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13
Q

PBB

A

Primary Bonding Busbar
The dedicated extension of the building ac grounding electrode system for the telecom infrastructure

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14
Q

RFI

A

Radio Frequency Interference
Electromagnetic interference in the radio frequency spectrum

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15
Q

SBB

A

Secondary Bonding Busbar
The grounding connection point for telecom infrastructure systems and telecom equipment in the area being served by an ER or TR

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16
Q

SBG

A

Supplementary Bonding Grid

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17
Q

TBC

A

Telecom Bonding Conductor
A conductor that connects the telecom bonding infrastructure to the buildings service equipment ground

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18
Q

Zone of Protection

A

Area under a lightning protection system

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19
Q

What term describes the establishment of a reference for the electrical power source, the electrical equipment of both?

A

Grounding

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20
Q

What term describes the connection intended to safely and effectively equalize the potential differences between two metallic items?

A

Bonding

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21
Q

What is a foreign electrical voltage or current?

A

Electrical voltages or currents not normally carried by or expected in telecom systems

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22
Q

Name four potential negative consequences of having a foreign voltage or current travel through a telecom system

A
  • Electrical shock
  • Destruction of equipment, fire
  • Component malfunction
  • Work or process distruption
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23
Q

Name six factors the ICT designer must consider in designing the telecom bonding infrastructure

A
  • Lightning
  • Ground potential rise (GPR)
  • Contact with electrical power circuits
  • EMI
  • RFI
  • EMC
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24
Q

True or False
The ICT designer is not responsible for engineering portions of electrical system related to ground faults, air terminal lightning protection, surge protection

A

True

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25
Q

When is the best time to design a bonding, grounding and protection scheme for a structure?

A

Initial planning and construction phases of a project

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26
Q

How should the ICT designer seek to resolve a conflict between a local safety code and the manufacturers requirements?

A

Ask the AHJ to resolve

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27
Q

Name the three subsystems that constitute a bonding and grounding system

A
  • ac grounding electrode systems
  • Equipment grounding system
  • Telecom bonding infrastructure
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28
Q

What is the purpose of the ac grounding (earthing) electrode system?

A
  • Establishes a 0V reference for ac electrical power systems
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29
Q

Name the two main components of the ac grounding (earthing) electrode system

A
  • Grounding electrode conductor (GEC)
  • Grounding (earthing) electrode
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30
Q

Which component of the ac grounding system can be used to connect the grounding electrode to the equipment grounding conductor?

A

The Grounding Electrode Conductor (GEC)

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31
Q

What device within the ac grounding electrode system is used to establish an electrical connection to the earth?

A

Grounding Electrode

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32
Q

Why does the ICT designer need to identify the type grounding electrode system used?

A

To make an effective connection

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33
Q

Where are telecom busbars installed when when building steel is used as a grounding electrode?

A

On a steel member within the ER, TR or EF

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34
Q

True or False
The ICT designer should bond the telecom infrastructure to the buildings metallic pipes

A

False
It is permissable but not recommended

35
Q

Typically, who is responsible for specifying the test criteria for the grounding system?

A

Qualified Electrical Designer

36
Q

When should the ac grounding electrode system be tested?

A

After the grounding infrastructure is installed but before final approval of it

37
Q

What is the best possible reading for any bonding conductor when measuring ac current?

A

0 A

38
Q

What is the recommended maxuimum ac current value on any bonding conductor?

A

Less than 1 A

39
Q

What is the recommended maximum dc current value on any bonding conductor?

A

Less than 500 mA

40
Q

What should be done if testing reveals an abnormally high ac current level on a bonding conductor?

A

Electrical main individual should be contacted immediately

41
Q

What type of tester is used for two point bonding measurements?

A

Earth grounding resistance tester that is configured for a continuity test

42
Q

What is the recommended bonding resistance between grounding electrode and busbar in the EF?

A

0.1 ohms

43
Q

What is the acceptable bonding resistance between the nearest available grounding electrode and busbar in the EF of a central office facility?

A

Less than 0.1 ohms

44
Q

What is the primary purpose of the telecom equipment grounding system?

A

To keep people safe and reduce fire hazards

45
Q

What is the main component of the telecom equipment grounding system?

A

Equipment grounding conductor

46
Q

What term is used to describe the total opposition of electrical current in ac circuits or an ac waveform imposed on a dc or ac circuit or conductor?

A

Impedance

47
Q

Name two forces that influence the impedance of an electrically conductive path

A
  • Inductive reactance
  • Capacitance reactance
48
Q

What are the recommended maximum impedance values for telecom euipment grounding conductors?

A

1 ohm for 120v and 0.8 ohms for 277v

49
Q

Name three negative consequences that may occur if the impedance exceeds its maximum value

A
  • Equipment operator shock
  • Equipment or structure fire
  • Equipment malfunction
50
Q

What instrument is used to measure impedance?

A

Ground impedance tester

51
Q

True or False
Most ground impedance testers can be used to uncover improper wiring?

A

True

52
Q

What is the benefit of using an isolated ground?

A

Reduces EM and RFI

53
Q

Name two ways that isolation ground receptacles can be identified

A
  • Solid orange receptacle coloring
  • Marked with an orange triangle
54
Q

An IG system is not recommended for use in customer premises voice and data systems. Why?

A

May defeat the purpose of an equipotential plane that is desirable in all EF, ER and TRs

55
Q

What is the purpose of a supplementray bonding grid (SBG)?

A

To provide a low impedance path between many cabinets or racks of telecom equipment

56
Q

What is the overall purpose of the telecom bonding infrastructure?

A

To equalize potentials between metallic surfaces in the event of electrical system faults

57
Q

Where do telecom bonding and grounding begin in a small ER or EF

A

At the PBB

58
Q

Which component serves as the central attachement point for all telecom bonding and grounding connections in a small system?

A

PBB

59
Q

What are the minimum dimensions for a PBB?

A

0.25 in thick by 4 in wide

60
Q

Why should the PBB be located as near as possible to the telecom cable EF?

A

Surge currents need to be equalized before they penetrate the telecom infrastructure

61
Q

What is the intended purpose of a TBC?

A

To bond the PBB to the ac grounding electrode system via the ac main service entrance panelboard

62
Q

What is the purpose of an SBB?

A

To serve the grounding connection point for telecom infrastructure systems

63
Q

What are the minimum dimensions of an SBB?

A

.025 in thick by 2 in wide

64
Q

Why should the SBB be referenced to the telecom ground terminal of the nearest ac electrical panelboard?

A

To equalize the potentials during lighting, electrostatic discharge and EMI conditions

65
Q

What is a TBB?

A

The TBB is a TBC that is intended to equalize potentials between TRs on mulitple floors or multipe TRs on the same floor

66
Q

What is the relationship between impedance and length of a TBB?

A

Impedance increases with the length, which reduces the TBBs ability to equalize potentials between ERs, TRs and EFs

67
Q

What is an alternative method to using a TBB in the system for a large site?

A

Specify the SBB in each TR be bonded to the structural steel if present and to the nearest ac electrical panelboard

68
Q

Which component is intended to equalize potentials between TRs on the same floor of a structure where multiple TBBs are used?

A

Backbone Bonding Conductor (BBC)

69
Q

What is the minimum recommended size for a bonding conductor if its run will not exceed 100ft?

A

6 AWG

70
Q

How is the maximum resistance value for a conductor length calculated?

A

Divide 40V by the short time rating of the ac GEC

71
Q

Name two typical methods for making bonding connections

A
  • Bolts of crimps
  • Exothermic welding
72
Q

Name three factors that make it difficult to determine the integrity of a telecom bonding connection

A
  • Distance
  • Access
  • Existance of other parallel bonding connections
73
Q

Name four types of problems that can be revealed by visually inspecting a telecom bonding connection

A
  • Loose connections
  • Corrosion
  • Physical damage
  • System modifications
74
Q

What type of bonding method may be useful for cable trays when the mechanical integrity of the connection is questionable?

A

The conventionable method of bonding across sectional and angle brackets

75
Q

Why should the use of home runs of telecom bonding conductors within cable trays be avoided?

A

Prevents different lengths of conductors within the cable trays become a source of voltage and ultimately amperage due to impedance differences

76
Q

True or False
Using direct buried cable eliminates risk of lightning exposure

A

False

77
Q

Why is electrical power cable routed above aerial cable?

A

To intercept and divert direct lightning strikes

78
Q

What term is used to describe an outdoor telecom cables susceptibility to electrical power system faults or to lightning or other transients?

A

Exposure

79
Q

When is telecom cable considered electrically exposed?

A

When any of its branches or individual circuits are exposed?

80
Q

What term is used to describe the area under or nearly under a lightning protection system?

A

Zone of Protection

81
Q

What term is used to refer to a simplified zone of protection?

A

Cone of Protection

82
Q

Name the five factors used to estimate loss due to lighting

A
  • Type of structure
  • Relative location
  • Lightning strike consequences
  • Occupancy
  • Lightning frequency
83
Q

What steps should the ICT distribution designer take when cable exposure is in question?

A
  • Consider it exposed
  • Note as exposed in request for quote response

DB (19 decks)

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