simple National Electrical Code question

Feb 19, 2005 9 Replies
C

This is an electrical question pertaining to derating more than three conductors in a single run of conduit.



I am feeding a 54 amp, 220 amp tankless hot water heater, and a 5000 watt, 220v A/C with electric heat from the main panel through 1 1/4" conduit.


From the main electrical panel I am running 15 feet of #6 to the

tankless water heater through 1 1/4" conduit. Amd I plan to run 15 feet of #10 wire to the A/C through the same size conduit, and place the A/C on a 30 amp breaker.


There will be four current carry conductors in this conduit. I don't have a copy of National Electrical Code handy. The answer to this question can be found in the National Electrical next to ampacity capacity of wire size or conduit fill.


Can anyone help me calculate the derating of these conductors?


You can just email me the formula from the national electrical code.

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S

I hope it is a 220 VOLT heater not amp.

Depending on where you live you might need to also increase wire sizes due to ambient heat. If you run #4 and #8 there will be no problems.

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R

Using THHN wire :

#10 ampacity = 40 amps

4-6 wires - 80% derating 80% ampacity = 32 amps you require (5000/220)*125%=28 amps #10s on a 30 amp breaker is ok. Use a #10 ground

#6 = 75 amps

80% ampacity = 60 amps you require 54 * 125% = 68 amps - - 70 amp breaker so use #4 - good for 95*.8=76amps #4s on a 70 amp breaker. Use a #8 ground

A 1 inch conduit is all you will need. Just make sure you use THHN.

RE

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R

so, what you're saying is:

Does the NEC allow for 2 #10 wires and 2 #6 in a 1=BC conduit ? that's rather obvious., unless you want to run an additional =BD in conduit for the fun of it...

I could tell you how many #6's and how many #10's you can use in 1=BC rigid conduit but that would take all the fun out of it, now would it ? };-)

you're work is done ~>

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B

#10 may carry 40a however, 90 degree Celsius terminals do not exist.

#10 ampacity = 40 amps

4-6 wires - 80% derating 80% ampacity = 32 amps you require (5000/220)*125%=28 amps #10s on a 30 amp breaker is ok. Use a #10 ground

#6 = 75 amps

80% ampacity = 60 amps you require 54 * 125% = 68 amps - - 70 amp breaker so use #4 - good for 95*.8=76amps #4s on a 70 amp breaker. Use a #8 ground

A 1 inch conduit is all you will need. Just make sure you use THHN.

RE

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G

The terminals are not in the conduit he is derating

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B

What kind of dork uses #10 for a 40a load?

The terminals are not in the conduit he is derating

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P

| What kind of dork uses #10 for a 40a load?

A pyromaniac?

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B

Hey greg...my reply was to sqlit. Thanks for your useless interjection.

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