Ckts In Conduit

[Alwayslearningelec]

Anyone know the reason why the engineers are saying in the specs "no more than 3 circuits in a conduit"? Seems like a real waster of money and because fo derating issues. For MOST single phase branch circuits that would be 6 CCC's for three circuits.

 

[infinity]

Anyone know the reason why the engineers are saying in the specs "no more than 3 circuits in a conduit"? Seems like a real waster of money and because fo derating issues. For MOST single phase branch circuits that would be 6 CCC's for three circuits.

They don't think that contractors are smart enough to do a simple derating calculation. Based on the work I see in the field often the engineers are correct.

 

[LarryFine]

The magic number is 9 CCCs before derating causes a wire-size increase.

 

[jusme123]

In some cases the engineer wants the extra space in conduit for future circuit

 

[Alwayslearningelec]

The magic number is 9 CCCs before derating causes a wire-size increase.

Right. SO #12 THHN Cu is good for 25A @ 75 degree. So if you have 7-9 CCC in a conduit it's only good for 70% of it's ampacity(30A) at the 90 degree column? 21A??

 

[infinity]

Right. SO #12 THHN Cu is good for 25A @ 75 degree. So if you have 7-9 CCC in a conduit it's only good for 70% of it's ampacity(30A) at the 90 degree column? 21A??

Close. #12 THHN rated for 30 amps @ 90° C. 30*80%=24 amps, 30@70%=21 amps. The "magic number" really only applies to #14, #12 and maybe #10 conductors.

 

[Alwayslearningelec]

Close. #12 THHN rated for 30 amps @ 90° C. 30*80%=24 amps, 30@70%=21 amps. The "magic number" really only applies to #14, #12 and maybe #10 conductors.

Close? 7-9 THHN Cu #12 conductors bundled together are good for 21A? Like I said? Thanks

 

[LarryFine]

Close?

I think he was critiquing your math, not your result, which is correct.

 

[qcroanoke]

Close. #12 THHN rated for 30 amps @ 90° C. 30*80%=24 amps, 30@70%=21 amps. The "magic number" really only applies to #14, #12 and maybe #10 conductors.

They don't like it when I point that out.

 

[infinity]

Close? 7-9 THHN Cu #12 conductors bundled together are good for 21A? Like I said? Thanks

You mentioned that #12 THHN was good for 25 amps. I said close because with only few exceptions #12 THHN is only good for 20 amps due to the limitation in article 240.