MIL-HDBK-419A Volume 1.txt

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MIL-HDBK-419A Volume 1.txt
2014-10-24 01:20:38

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  1. What are the four basic subsystems of grounding, bonding and shielding?
    An earth electrode subsystem, A lightning protection subsystem, A fault protection subsystem, A signal reference subsystem.
  2. The __________ subsystem includes the following: (1) a system of buried, driven rods interconnected with bare wire that normally form a ring around the building; or (2) metallic pipe systems, i.e., water, gas, fuel, etc., that have no insulation joints;or (3) a ground plane of horizontal buried wires.
    earth electrode
  3. The ___________ subsystem provides a nondestructive path to ground for lightning energy contacting or induced in facility structures.
    lightning protection
  4. Power line filters should not induce more than ___ milliamperes of current to the fault protection subsystem.
  5. A lightning flash is characterized by one or more strokes with typical peak current
  6. amplitudes of _____ kAor higher
    20 kA
  7. Ground fault circuit interrupters on 120 volt single phase ___ and ____ ampere circuits will provide personnel protection against power faults and their use is therefore highly recommended
    15, 20
  8. Ideally, the earth electrode subsystem provides ______ resistance between the earth and the point of connection.
  9. Metal underground water pipes typically exhibit a resistance to earth of less than
  10. ______ ohms.
  11. Other metal elements in contact with the soil such as the metal frame of the building, underground gas piping systems, well casings, other piping and/or buried tanks, and concrete-encased steel reinforcing bars or rods in underground footings or foundations generally exhibit a resistance substantially lower than ___ ohms
  12. For the fault protection subsystem, the NEC (2-2) states in Article 250 that a single electrode consisting of a rod, pipe or plate which does not have a resistance to ground
  13. of ___ ohms or- less shall be augmented by one additional made electrode
  14. A compromise of cost versus protection against lightning, power faults, or EMP has led to establishment of a design goal of ____ ohms for the earth electrode subsystem (EES) in MIL-STD-188-124A.
  15. The current which flows in a direct lightning stroke may vary from several hundred amperes to as much as _____ thousand amperes.
  16. Experience has shown that a grounding resistance of ___ ohms gives fairly reliable lightning protection to buildings, transformers, transmission lines, towers, and other exposed structures.
  17. Earth electrode subsystems can be divided into two general types, the most preferable being a ring ground with _______ minimum length ground rods every _________.
    3 meter, 15 feet (4.5 meters)
  18. Rods or pipes are generally used where bedrock is beyond a depth of __________.
    3 meters (10 feet)
  19. Ground rods are commercially manufactured in _________ diameters and in lengths from____ to ___meters.
    1.27, 1.59, 1.90 and 2.54 cm (1/2, 5/8, 3/4 and 1 inch)
  20. 1.5 to 12 meters (5 to 40 feet).
  21. For most applications, ground rods of ___________ diameter, and length of ________, are used.
    1.90 cm (3/4 inch), 3.0 meters (10 feet)
  22. Horizontal strips of metal buried ___________ inches deep may be used in place of driven ground rods where bedruck is near the surface of the earth.
    18 to 36 inches
  23. In measuring a single 3 meter (10-foot) driven ground rod, the distance between the three separate ground electrodes should be at least ___________, with a
  24. preferable spacing of _____________ or more.
    5 meters (15 feet), 8 meters (25 feet)
  25. To an observer at a specific location, the average distance at which lightning may occur and thunder will be heard is about ________
    10 km (6 miles)
  26. The NFPA Lightning Protection Code (3-9) recommends that a ___ zone of protection be provided in important areas while a ____ zone is acceptable for less important areas.
    1:1 , 2:1
  27. Signal ground system is electrically isolated from the building ground and other conductive objects.
    Floating Ground
  28. the signal circuits are referenced to a single point, and this single point is then
  29. connected to the facility ground.
    Single-Point Ground
  30. Utilizes many conductive paths from the earth electrode subsystem to various electronic systems or subsystems within the facility.
    Multipoint Ground
  31. The American National Standards Institute (9-3) limits the maximum allowable leakage current to _____ milliamps for portable two-wire devices and ____ milliamps for heavy movable cord-connected equipment in order to prevent involuntary shock reactions.
    0.2, 0.75
  32. For calculation purposes, the resistance of the skin is usually taken to be somewhere between _____ and _____ohms.
    500, 1500
  33. The reaction current is ____ to ___ milliamps.
    1 to 4
  34. The perception current usually lies between __ and __ milliamps for men and women, the exact value depending on the individual.
    0, 1
  35. The ‘let-go” current varies between ___ - ___ milliamps, depending on the individual
    4, 21
  36. Shock currents above about __ milliamps can cause the muscles of the chest to contract and breathing to stop.
  37. Below ____ MHz, rf energy penetrates deeply into the body.
  38. The power absorbed in the body tissues can be as high as ____ of the incident power.
  39. In the _____ GHz region of the rf spectrum, the eyes and the testes are the most vulnerable organs to rf radiation damage.
  40. The maximum safe exposure to X-ray radiation is considered to be ___ milli-Roentgens per week