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# 100AMP breaker/ Wiring Size!

#1
03-03-05, 07:06 AM
garo24
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100AMP breaker/ Wiring Size!

If one was to run a 100 AMP circuit breaker from Main Panel to feed a subpanel, what wire would be correct to use? According to Square D, the 100 Amp breaker (QO2100) is rated at 100AMP at 75 degrees Celsuis. According to this chart, http://ecatalog.squared.com/pubs/Cir...0600DB0103.pdf, one must use the correct conductor that is rated for 75 degrees celsuis, thus being #3 copper rated for 100Amps.

It also talks about 90 degree celsuis conductors, they can be used with 60/75 degree C, but their wire size must be rated for the lower temperature-rated wire. Does this mean that one could use #4, insulation type 90 degrees celsuis which is rated 95 amps?

#2
03-03-05, 08:30 AM
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Location: Dry Side of Washington State
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Originally Posted by garo24
If one was to run a 100 AMP circuit breaker from Main Panel to feed a subpanel, what wire would be correct to use? According to Square D, the 100 Amp breaker (QO2100) is rated at 100AMP at 75 degrees Celsuis. According to this chart, http://ecatalog.squared.com/pubs/Cir...0600DB0103.pdf, one must use the correct conductor that is rated for 75 degrees celsuis, thus being #3 copper rated for 100Amps.

It also talks about 90 degree celsuis conductors, they can be used with 60/75 degree C, but their wire size must be rated for the lower temperature-rated wire. Does this mean that one could use #4, insulation type 90 degrees celsuis which is rated 95 amps?
Is this in a residence?

#3
03-03-05, 08:35 AM
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Wire can virtually never be used at its 90-degree ampacity, because 90-degree terminations are practically non-existent (at least for the residential user). The 75-degree ampacity is the best you can do in almost all cases, and the 60-degree ampacity is the best you can do for most cable assemblies and for #10 or smaller.

#4
03-03-05, 09:05 AM
garo24
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Yes this is in a residence.

#5
03-03-05, 10:43 AM
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Originally Posted by garo24
Yes this is in a residence.
NEC 2002 allows using #4 AWG copper or #2 aluminum feeders based on the 100 amp circuit breaker supplying the subpanel.

#6
03-03-05, 11:16 AM
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Thinman, which table did you get that from?

#7
03-03-05, 01:03 PM
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I was using Article 240.4 Protection of Conductors (B) Devices Rated At 800 Amperes or Less(2) using the next size circuit breaker if there is no standard circuit breaker that corresponds to the conductor's ampacity. I plum forgot about a 90 amp circuit breaker being a standard breaker. So, #4 AWG copper and #2 AWG aluminum have to be protected by a 90 amp breaker not a 100 amp breaker.

My apologies for the wrong info.

#8
03-03-05, 05:57 PM
garo24
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so I can use #2 cu with the 100 Amp breaker then?

3 #2 wires
1 #6 ground wire

2 hot, 1 neutral, 1 ground

#9
03-03-05, 07:13 PM
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Same answer as yesterday. Still yes.

#10
03-03-05, 07:39 PM
waterfowelman
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#2 Who?

yOU COULD USE # 3'S IFEN YA WANT2

JD.