70A feeders #6 wire?

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LEO2854

LEO2854

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Edwardtomas said:
Hi
Can l use #6 copper wire to feed sub panel that has 70a main cir.brkr in the swbd
In a residential multiunit apart. Bldg
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No,not unless your connections are rated for 90deg C.

110.14(C) Temperature Limitations. The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.(1) Equipment Provisions. The determination of termination provisions of equipment shall be based on 110.14(C)(1)(a) or (C)(1)(b). Unless the equipment is listed and marked otherwise, conductor ampacities used in determining equipment termination provisions shall be based on Table 310.15(B)(16) as appropriately modified by 310.15(B)(7).
(a)?
Termination provisions of equipment for circuits rated 100 amperes or less, or marked for 14 AWG through 1 AWG conductors, shall be used only for one of the following:
(1)?
Conductors rated 60?C (140?F).
(2)?
Conductors with higher temperature ratings, provided the ampacity of such conductors is determined based on the 60?C (140?F) ampacity of the conductor size used.
(3)?
Conductors with higher temperature ratings if the equipment is listed and identified for use with such conductors.
(4)?
For motors marked with design letters B, C, or D, conductors having an insulation rating of 75?C (167?F) or higher shall be permitted to be used, provided the ampacity of such conductors does not exceed the 75?C (167?F) ampacity.
(b)?
Termination provisions of equipment for circuits rated over 100 amperes, or marked for conductors larger than 1 AWG, shall be used only for one of the following:
(1)?
Conductors rated 75?C (167?F)
(2)?
Conductors with higher temperature ratings, provided the ampacity of such conductors does not exceed the 75?C (167?F) ampacity of the conductor size used, or up to their ampacity if the equipment is listed and identified for use with such conductors
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ActionDave

ActionDave

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Edwardtomas said:
Hi
Can l use #6 copper wire to feed sub panel that has 70a main cir.brkr in the swbd
In a residential multiunit apart. Bldg
Click to expand...
Need some more info to say for sure. What is the wiring method? #6 NMB, no. #6 THHN, maybe.

Also since it is a sup-panel what size is the breaker on the line side? 50A, then yes every time.
 
infinity

infinity

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If you're using a 75? C wiring method such as MC cable or THHN in a raceway then you could use the 70 amp OCPD with #6 conductors. The calculated load would need to be 65 amps or less.
 
buzzbar

buzzbar

Senior Member
Location
Olympia, WA
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Electrical Contractor
infinity said:
#6 THHN or MC cable = 65 amps, next standard size 70 amp OCPD.
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I agree. If we all agree that the ampacity is 65 amps, then you can put it on a 70 amp breaker because it's the next standard fuse size over 60 amp. I reference 240.4(B):

(B) Devices Rated 800 Amperes or Less. The next higherstandard overcurrent device rating (above the ampacity ofthe conductors being protected) shall be permitted to beused, provided all of the following conditions are met:

  1. (1) The conductors being protected are not part of a mul-tioutlet branch circuit supplying receptacles for cord-and-plug-connected portable loads.
  2. (2) The ampacity of the conductors does not correspondwith the standard ampere rating of a fuse or a circuitbreaker without overload trip adjustments above its rat-ing (but that shall be permitted to have other trip orrating adjustments).
  3. (3) The next higher standard rating selected does not ex-ceed 800 amperes.





The standard fuse sizes are found at 240.6(A):

240.6 Standard Ampere Ratings.
(A) Fuses and Fixed-Trip Circuit Breakers. The stan-
dard ampere ratings for fuses and inverse time circuitbreakers shall be considered 15, 20, 25, 30, 35, 40, 45, 50,60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300,350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000,2500, 3000, 4000, 5000, and 6000 amperes. Additionalstandard ampere ratings for fuses shall be 1, 3, 6, 10, and601. The use of fuses and inverse time circuit breakers withnonstandard ampere ratings shall be permitted.
 
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