Maximum number of wires in 1/2" conduit

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Old 04-05-05, 07:50 PM
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Maximum number of wires in 1/2" conduit

My book says that I put:

- six 12 gauge wires
or
- five 10 gauge wires

... in 1/2" metal conduit. The guy at Home Depot said I'm not allowed to put *any* 10-gauge wires inside of 1/2" conduit.

Who is right?

-Antun
 
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Old 04-05-05, 08:10 PM
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Antun, it actually depends on the type of wire and how it is insulated. the most common wire in conduit for residential purposes is thhn/thwn. This desigantion will be printed on the outside cover of the wire. Assuming you are using thhn/thwn you can put 9 conductors that are #12 awg or 6 conductors that are #10 awg in 1/2" rigid metal conduit. If you are using a different type wire then these numbers will likely change. You must also derate the ampacity for more than 3 current carrying conductors in a conduit/raceway.
 

Last edited by Roger; 04-05-05 at 10:07 PM. Reason: correction
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Old 04-05-05, 09:23 PM
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What book told you this if I may ask?

Roger answered your question well but I will just make two comments.

Derating starts at 3 current carrying conductors, but we derate from the 90 deg C column. So for #14, #12 & #10 you need over 9 cc conductors to make a difference. Under 9 the amperages stay the same, even though you are derating. If that makes ANY sense at all.

Second, NEVER listen to a home center employee!!!! Your life may depend on it someday!
 
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Old 04-05-05, 09:31 PM
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My book says:

TW, #12 = 7 conductors
THW, #12 = 4 conductors
THWN, #12 = 10 conductors

Can you even get 10, 12 gauge conductors to fit into a half inch piece of pipe?
 
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Old 04-05-05, 10:09 PM
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The Black & Decker Complete Guide to home wiring. It does mention the THHN/THWN designation, but I assumed that's what I had.

-Antun


Originally Posted by Speedy Petey
What book told you this if I may ask?
 
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Old 04-05-05, 10:12 PM
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So here's what I want to do:

- Put three 10-gauge wires in there (there are already three of them there; I plan to remove & replace these).
- Add an additional two 12-gauge wires in.

So I will have 8 wires in total. It sounds like I'm OK there.

Thanks,

Antun

Originally Posted by Speedy Petey
Derating starts at 3 current carrying conductors, but we derate from the 90 deg C column. So for #14, #12 & #10 you need over 9 cc conductors to make a difference. Under 9 the amperages stay the same, even though you are derating. If that makes ANY sense at all.
 
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Old 04-05-05, 10:19 PM
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Antun, I would say that black and decker is talking about EMT (electrical metallic tubing) this would explain the 5 # 10's but it would appear they have a misprint on the #12's. this would be 9 whether EMT or RMC conduit. They also might have meant 12 #14 awg in 1/2" EMT.
 
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Old 04-05-05, 10:31 PM
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Here's a handy calculator I found...

http://www.electrician.com/calculato...alculator.html
 
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Old 04-05-05, 10:32 PM
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Thanks Roger

I take it that means I can put three 10s and two 12s in there?

-Antun

Originally Posted by Roger
Antun, I would say that black and decker is talking about EMT (electrical metallic tubing) this would explain the 5 # 10's but it would appear they have a misprint on the #12's. this would be 9 whether EMT or RMC conduit. They also might have meant 12 #14 awg in 1/2" EMT.
 
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Old 04-05-05, 10:36 PM
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You are ok by .0321 sq. inches if you are dealing with EMT and .0351 sq. inches if RMC.
 

Last edited by Roger; 04-05-05 at 10:59 PM.
 

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