MIL-STD-188-124B Grounding, bonding, shielding

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Anonymous
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269911
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MIL-STD-188-124B Grounding, bonding, shielding
Updated:
2014-04-09 13:55:46
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grounding
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bonding
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  1. The Facility Ground System consists of:
    1. The earth electrode subsystem2. The fault protection subsystem3. The lightning protection subsystem4. The signal reference subsystem
  2. What is the purpose of a bond?
    To prevent development of electrical potentials between individual metal surfaces for all frequencies capable of causing interference.
  3. What is the purpose of shielding?
    To prevent the equipment from propagating interference and to protect the equipment from the effects of interference propagated by other electrical and electronic devices.
  4. What is the purpose of an earth electrode subsystem?
    To provide a low resistance path to earth for lightning and power fault currents and ensure hazardous voltages do not occur within the facility.
  5. How far outside the drip line of structures are ground rods placed?
    0.6m to 1.8m (2' to 6')
  6. Ground rods are interconnected with _________ which is buried at least ________ below grade level.
    1/0 AWG bare copper cable, .45m (1.5')
  7. How is the ground rods interconnecting cable connected to the ground rods?
    brazed or welded (In the case of ground wells, acceptable compression type connectors may be utilized)
  8. The resistance to earth of the earth electrode subsystem should not exceed _______.
    10 ohms
  9. What are ground rods made of?
    Copper-clad steel
  10. What are the dimensions of a ground rod?
    Minimum of 3' in length, no less than 1.9cm (3/4") in diameter. The copper jacket shall not be less than .3mm (0.012")
  11. How far apart are ground rods placed?
    Uniformly spaced apart not more than twice the rod length.
  12. How should resistance to earth of the earth electrode subsystem be measure?
    By the fall of potential technique
  13. What is the purpose of the fault protection subsystem?
    Consists of a separate grounding conductor (green wire) to provide personnel and equipment protection against power fault currents and static charge buildup.
  14. How is protection from ligthning flashover accomplished?
    By grounding all major non-current-carrying
  15. What types of items are grounded to the facility ground system?
    Building structural steel, pipes and tubes, electrical support structures, conduit, etc.
  16. What types of items are grounded to the facility ground system?
    Buildign structural steel, pipes and tubes, electrical support structures, conduit, etc.
  17. Metallic cable tray assemblies should be connected to ground within ____________ of each end of the run and every _____________ along each run.
    0.6m (2'), 15m (50')
  18. AC power distribution systems shall have the neutral conductor grounded at ______________
    The distribution transformer and to the earth electrode subsystem of the facility.
  19. In copper-clad steel down conductors used on structures not greaeter than 23m (75') in height, the dc resistance of solid wires or stranded cables shall not be greater than
    0.176 ohms per 305m (1000')
  20. In copper-clad steel down conductors used on structures greater than 23m (75') the dc resistance of the wire or cable shall not be greater than
    0.088 ohms per 305m (1000')
  21. Copper-clad stranded cable down conductors shall not be les than
    No. 14 AWG (unless mechanical and installation situations warrant a larger wire)
  22. The conductivitiy of copper clad down conductors shall not be less than ________ of a solid coper conductor of equivelant cross-sectional area
    30%
  23. Down conductors bends shall be gradual and not have a radius less than __________
    20cm (8")
  24. Down conductor bend angles shall not be less than ________
    90 degrees
  25. Metal objects within ______ of a lightning download shall be bonded to the conductor
    1.8m (6')
  26. Waveguides to an antenna shall be grounded at how many points?
    3: Near the antenna, at the vertical to horizontal transition near the base of the tower and at the waveguide entry port.
  27. Waveguides shall be grounded with solid copper strap or copper wire at least equal to
    14 awg
  28. What is the purpose of the signal reference subsystem?
    To control static charges and noise, and establish a common reference for signals between sources and loads
  29. Higher frequency networks may require an ____________
    Equipotential plane
  30. Equipotential planes may consist of
    A solid sheet or wire mesh
  31. A mesh will appear electrically as a solid sheet as long as the mesh openings are _________ or less at the highest frequencies of concern.
    1/8 lambda (whatever the heck that means)
  32. The maximum allowable mesh size is _________
    4"
  33. The equipotential plane should be installed ___________
    overhead
  34. What qualifies as a lower frequency network?
    DC to 30Khz (sometimes up to 300Khz)
  35. What is the purpose of a lower frequency network?
    To isolate lower frequency signals from all other ground networks
  36. What type of earth electrode subsystem works on lower frequencies?
    Singlie point
  37. What is the purpose of the fault protection subsystem?
    To ensure that personnel are protected from shock hazard and the equipment is protected from damage resulting from faults.
  38. What is a GFCI?
    Ground Fault Circuit Interrupter
  39. All bonds for ground conductors whose purpose is to provide a path for power, control, or signal currents and lightning protection shall have a maximum dc resistance of
    1 milliohm (0.001 ohm)

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