codes&practices3.txt

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Author:
johnbowens
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49493
Filename:
codes&practices3.txt
Updated:
2011-12-24 16:23:44
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codes practices OCPD
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OCPD and the NEC
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  1. Typically an OCPD is rated at ________% of the continuous load current. An exception to this general rule that allows a sizing at a larger percentage would be_______ loads. NJATC, Codes and Practices 3, WB PP 8 & NEC 210.19A1
    • 125%
    • motor; unless the equipment listing determines a different rating, according to 210.20 (overcurrent protection) 210.20 refers you to T240.3 for specific equipment protection.
  2. A circuit breaker with a slash rating, such as 120/240, shall be permitted to be applied where? NJATC, Codes and Practices 3, WB PP 11
    Solidly grounded system. Not in a corner grounded, resistance grounded, or ungrounded system.
  3. Branch circuit ocpd's are never rated less than what interrupting rating? NJATC, Codes and Practices 3, WB PP 10
    5000 amps
  4. Dual element fuses generally are permitted to be sized up to _______% and an inverse time circuit breaker up to ____% of the motor full load amperes. NJATC, Codes and Practices 3, WB PP 12
    • 175%
    • 250%
  5. According to 240.83(C) the interrupting rating of an OCPD is/ is not required to be marked on a circuit breaker used for supplementary protection. NJATC, Codes and Practices 3, WB PP 15
    Is not
  6. The mechanical trip unit on a circuit breaker can be what? NJATC, Codes and Practices 3, WB PP 17
    • Thermal magentic
    • Magnetic only
    • Electronic trip
  7. A branch circuit breaker can be thermal magnetic, electronic trip, or? NJATC, Codes and Practices 3, WB PP 20
    Current limiting.
  8. What type of element is often used to trip a thermal magnetic trip circuit breaker on an overload condition? NJATC, Codes and Practices 3, WB PP 18
    Bi-metal
  9. What portion of a molded case circuit breaker is used for overload protection. NJATC, Codes and Practices 3, WB PP 21
    Thermal trip.
  10. Low voltage circuit breaker are typically used where? NJATC, Codes and Practices 3, WB PP 24
    Draw out capability or selective coordination is required for maintenance.
  11. Thermal magnetic molded case circuit breakers are also known as what? Why? NJATC, Codes and Practices 3, WB PP 20
    • Inverse time circuit breakers
    • This is because the higher the overcurrent, the faster the breaker trips.
  12. For a 20A circuit breaker the fixed instantaneous setting may be _____ times the circuit breaker rating. NJATC, Codes and Practices 3, WB PP 22
    8
  13. What kind of circuit breaker is not considered used in branch circuits and typically cannot replace the thermal magnetic or electronic trip circuit breaker? NJATC, Codes and Practices 3, WB PP 23
    Magnetic only trip circuit breakers often referred to as mag- only, or instantaneous trip only circuit breakers.
  14. One benefit of current-limiting fuses is what? Specifically how many amps? NJATC, Codes and Practices 3, WB PP 27
    • Interrupting rating
    • 200,000 amps or higher
  15. Non-time delay (fast acting) fuses use what type of element? NJATC, Codes and Practices 3, WB PP 27
    Single.
  16. A time delay fuse is a single or dual element fuse? NJATC, Codes and Practices 3, WB PP 27
    Dual- element.
  17. What class fuse cannot be replaced with a class H fuse? NJATC, Codes and Practices 3, WB PP 32
    Class R.
  18. What class fuse is used in lighting? NJATC, Codes and Practices 3, WB PP 32
    T (300v)
  19. Typically current limiting rejection style fuses have a min. interupting rating of? NJATC, Codes and Practices 3, WB PP
    200,000A
  20. Most faults are from what to what? NJATC, Codes and Practices 3, WB PP
    Phase to ground
  21. Fuses are conected in series or parallel with the load? NJATC, job information workbook 1, PP 141

    There are 3 basic ways a fuse is rated. They are? NJATC, Job Info WB 1, PP 142
    series

    • Ampere
    • interrupting current
    • voltage or slash rating
  22. Although there are exception, generally, the ampere rating of a fuse and switch combination should be selected at ________of the load current. NJATC, Job Info WB 1, pp 143

    Is this the same as the 80% rule for ampacity of conductors?
    125%

    • Yes. 125% of 20A (load current) = 25A fuse/ switch rating.
    • 80% of 25A (fuse/ switch rating) = 20A (load current)
  23. The branch circuit calculations must be based on what rule regarding percentage of load? NJATC, Codes and Practices 3, WB PP 11 & NEC 210.20A
    Branch circuit calculations must be based on 100% of the non-continuous load plus 125% of the continuous load.

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