ampacity

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efren

Member
What is the ampacity of 10 #10 THHN copper conductor in the same conduit and what size
conduit can I use.

For 10 ingle phase 208 circuits my engineer is using # 8 THHN wire and 1 1/2 conduit (10 # 8 and 1 # 8 ground inside the conduit) is she OK???
 

ryan_618

Senior Member
Re: ampacity

The ampacity would be 20 amps, and you could legally cram them into a 3/4" EMT. I don't know of anyone who would try this, but it could be done. :) If you were to pull an equipment grounding conductor as opposed to using the raceway as the EGC, a 1" EMT would be required.
 

charlie b

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Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
Re: ampacity

The ampacity of ten #10 THHN copper is 20 amps, as Ryan has said. And yes, you can put eleven #8 THHN into a 1 1/2 inch conduit. But in that case, the ampacity would be 27.5 amps (i.e., 55 amps times a 50% derating factor). However, did you mean to say ?10 circuits?? A circuit has 2 wires, so 10 circuits would have 20 wires. Please note that you could still put twenty #8 THHN and one #8 EGC into a 1 1/2 inch conduit, and the ampacity would still be 27.5 amps. But as Ryan said earlier, that would be a difficult installation.

I can?t comment on whether the engineer is ?OK,? because you did not tell us enough about the proposed design (e.g., what is the required ampacity, and how long is the run?).
 

efren

Member
Re: ampacity

Charlie,there is only 5, 20 amp, 208V single phase
(no neutral)circuits and the run is only about 50' long.
She keeps on using the 60 degree table to derate
the run instead of the 90 degree.

she said I must use # 8 wire and 1 1??/2" conduit.

I think I can use smaller wire and pipe
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Re: ampacity

You can use smaller pipe and wire, but it is still code compliant. She should use the 90 degree table, but it still works, just overkill. You just will not have much voltage drop, and a cool pipe.
 

iwire

Moderator
Staff member
Location
Massachusetts
Re: ampacity

The job is either contract or T&M.

If it is T&M put in what they ask and make money doing it.

If it is contract work and that was on the plan you gave a price on you owe them what they are paying for.

That is unless you are planning on giving a credit.
 

charlie b

Moderator
Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
Re: ampacity

Dereck and Bob are right, but I?ll put it in different terms. The NEC provides the minimum requirements for a safe installation. If she wants to go above and beyond the minimums, then that would not be in violation of the code. However, presuming the circuit requires no more than a 20 amp?s worth of conductors (you still have not confirmed this), her assertion that you MUST use # 8 wire and 1 1 /2" conduit is not correct. A more accurate statement is that you must use at least #10?s, and you may, if you wish, use a larger wire.
 
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