TDMM Chapter 8 Flashcards
ac
Alternating Current
A current flow that alternates periodically (usually sinusoidal) in magnitude and direction
BBC
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
Bonding
The connection intended to safely and effectively equalize the potential differences between two metallic items
dc
Direct Current
Current flow that has a constant direction. The letters dc are also used generically to refer to any constant waveform.
EMC
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
EMI
Electromagnetic Interference
Radiated of conducted electromagnetic energy that has an undesirable effect on electronic equipment or signal transmissions
GEC
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
GPR
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
Grounding
The establishment of a reference for the electrical power source, the electrical equipment or both
IG
Isolated Ground
An equipment grounding topology that presumably reduces the effects of EMI or RFI on the equipment grounding system
Impedance
The total opposition of electrical current in ac circuits or an ac waveform up a dc or ac circuit or conductor
Lightning Exposure
An outdoor telecom cables susceptibility to electrical power system faults or to lighting or other transients
PBB
Primary Bonding Busbar
The dedicated extension of the building ac grounding electrode system for the telecom infrastructure
RFI
Radio Frequency Interference
Electromagnetic interference in the radio frequency spectrum
SBB
Secondary Bonding Busbar
The grounding connection point for telecom infrastructure systems and telecom equipment in the area being served by an ER or TR
SBG
Supplementary Bonding Grid
TBC
Telecom Bonding Conductor
A conductor that connects the telecom bonding infrastructure to the buildings service equipment ground
Zone of Protection
Area under a lightning protection system
What term describes the establishment of a reference for the electrical power source, the electrical equipment of both?
Grounding
What term describes the connection intended to safely and effectively equalize the potential differences between two metallic items?
Bonding
What is a foreign electrical voltage or current?
Electrical voltages or currents not normally carried by or expected in telecom systems
Name four potential negative consequences of having a foreign voltage or current travel through a telecom system
- Electrical shock
- Destruction of equipment, fire
- Component malfunction
- Work or process distruption
Name six factors the ICT designer must consider in designing the telecom bonding infrastructure
- Lightning
- Ground potential rise (GPR)
- Contact with electrical power circuits
- EMI
- RFI
- EMC
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
True
When is the best time to design a bonding, grounding and protection scheme for a structure?
Initial planning and construction phases of a project
How should the ICT designer seek to resolve a conflict between a local safety code and the manufacturers requirements?
Ask the AHJ to resolve
Name the three subsystems that constitute a bonding and grounding system
- ac grounding electrode systems
- Equipment grounding system
- Telecom bonding infrastructure
What is the purpose of the ac grounding (earthing) electrode system?
- Establishes a 0V reference for ac electrical power systems
Name the two main components of the ac grounding (earthing) electrode system
- Grounding electrode conductor (GEC)
- Grounding (earthing) electrode
Which component of the ac grounding system can be used to connect the grounding electrode to the equipment grounding conductor?
The Grounding Electrode Conductor (GEC)
What device within the ac grounding electrode system is used to establish an electrical connection to the earth?
Grounding Electrode
Why does the ICT designer need to identify the type grounding electrode system used?
To make an effective connection
Where are telecom busbars installed when when building steel is used as a grounding electrode?
On a steel member within the ER, TR or EF
True or False
The ICT designer should bond the telecom infrastructure to the buildings metallic pipes
False
It is permissable but not recommended
Typically, who is responsible for specifying the test criteria for the grounding system?
Qualified Electrical Designer
When should the ac grounding electrode system be tested?
After the grounding infrastructure is installed but before final approval of it
What is the best possible reading for any bonding conductor when measuring ac current?
0 A
What is the recommended maxuimum ac current value on any bonding conductor?
Less than 1 A
What is the recommended maximum dc current value on any bonding conductor?
Less than 500 mA
What should be done if testing reveals an abnormally high ac current level on a bonding conductor?
Electrical main individual should be contacted immediately
What type of tester is used for two point bonding measurements?
Earth grounding resistance tester that is configured for a continuity test
What is the recommended bonding resistance between grounding electrode and busbar in the EF?
0.1 ohms
What is the acceptable bonding resistance between the nearest available grounding electrode and busbar in the EF of a central office facility?
Less than 0.1 ohms
What is the primary purpose of the telecom equipment grounding system?
To keep people safe and reduce fire hazards
What is the main component of the telecom equipment grounding system?
Equipment grounding conductor
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?
Impedance
Name two forces that influence the impedance of an electrically conductive path
- Inductive reactance
- Capacitance reactance
What are the recommended maximum impedance values for telecom euipment grounding conductors?
1 ohm for 120v and 0.8 ohms for 277v
Name three negative consequences that may occur if the impedance exceeds its maximum value
- Equipment operator shock
- Equipment or structure fire
- Equipment malfunction
What instrument is used to measure impedance?
Ground impedance tester
True or False
Most ground impedance testers can be used to uncover improper wiring?
True
What is the benefit of using an isolated ground?
Reduces EM and RFI
Name two ways that isolation ground receptacles can be identified
- Solid orange receptacle coloring
- Marked with an orange triangle
An IG system is not recommended for use in customer premises voice and data systems. Why?
May defeat the purpose of an equipotential plane that is desirable in all EF, ER and TRs
What is the purpose of a supplementray bonding grid (SBG)?
To provide a low impedance path between many cabinets or racks of telecom equipment
What is the overall purpose of the telecom bonding infrastructure?
To equalize potentials between metallic surfaces in the event of electrical system faults
Where do telecom bonding and grounding begin in a small ER or EF
At the PBB
Which component serves as the central attachement point for all telecom bonding and grounding connections in a small system?
PBB
What are the minimum dimensions for a PBB?
0.25 in thick by 4 in wide
Why should the PBB be located as near as possible to the telecom cable EF?
Surge currents need to be equalized before they penetrate the telecom infrastructure
What is the intended purpose of a TBC?
To bond the PBB to the ac grounding electrode system via the ac main service entrance panelboard
What is the purpose of an SBB?
To serve the grounding connection point for telecom infrastructure systems
What are the minimum dimensions of an SBB?
.025 in thick by 2 in wide
Why should the SBB be referenced to the telecom ground terminal of the nearest ac electrical panelboard?
To equalize the potentials during lighting, electrostatic discharge and EMI conditions
What is a TBB?
The TBB is a TBC that is intended to equalize potentials between TRs on mulitple floors or multipe TRs on the same floor
What is the relationship between impedance and length of a TBB?
Impedance increases with the length, which reduces the TBBs ability to equalize potentials between ERs, TRs and EFs
What is an alternative method to using a TBB in the system for a large site?
Specify the SBB in each TR be bonded to the structural steel if present and to the nearest ac electrical panelboard
Which component is intended to equalize potentials between TRs on the same floor of a structure where multiple TBBs are used?
Backbone Bonding Conductor (BBC)
What is the minimum recommended size for a bonding conductor if its run will not exceed 100ft?
6 AWG
How is the maximum resistance value for a conductor length calculated?
Divide 40V by the short time rating of the ac GEC
Name two typical methods for making bonding connections
- Bolts of crimps
- Exothermic welding
Name three factors that make it difficult to determine the integrity of a telecom bonding connection
- Distance
- Access
- Existance of other parallel bonding connections
Name four types of problems that can be revealed by visually inspecting a telecom bonding connection
- Loose connections
- Corrosion
- Physical damage
- System modifications
What type of bonding method may be useful for cable trays when the mechanical integrity of the connection is questionable?
The conventionable method of bonding across sectional and angle brackets
Why should the use of home runs of telecom bonding conductors within cable trays be avoided?
Prevents different lengths of conductors within the cable trays become a source of voltage and ultimately amperage due to impedance differences
True or False
Using direct buried cable eliminates risk of lightning exposure
False
Why is electrical power cable routed above aerial cable?
To intercept and divert direct lightning strikes
What term is used to describe an outdoor telecom cables susceptibility to electrical power system faults or to lightning or other transients?
Exposure
When is telecom cable considered electrically exposed?
When any of its branches or individual circuits are exposed?
What term is used to describe the area under or nearly under a lightning protection system?
Zone of Protection
What term is used to refer to a simplified zone of protection?
Cone of Protection
Name the five factors used to estimate loss due to lightning
- Type of structure
- Relative location
- Lightning strike consequences
- Occupancy
- Lightning frequency
What steps should the ICT distribution designer take when cable exposure is in question?
- Consider it exposed
- Note as exposed in request for quote response
