Conduit fill + derate Wires.

[Vinny Lima]

My boss and I are doing a small commercial job that is going o require some EMT to be installed, so we can pull our circuits over to a Junction jox which im going to be feeding outlets and lighting out of it. I got a total of 20 circuits at 20 amps , and im Using 1'1/2 EMT pipe. i also understand that the code says that i can pull up to 61 wires in that conduit and . the part that my boss and i are not very familiar with is the derating part it. we know that we have to derate the wires. But we couldnt find very explanatory in the code book . Could any one explain to me how this part works ?

ASAP ASAP ASAP ASAP ASAP

 

[infinity]

Take a look at 310.15(B)(2) and let us know what you come up with. For 20-20 amp circuits your 1.5" conduit it likely going to be too small.

Welcome to the forum.

 

[480sparky]

You first need to determine how many current-carrying wires you have.

Are you pulling a hot and neutral for each circuit, or are you using multi-wires? Single or three-phase?

 

[Mr. Wizard]

My boss and I are doing a small commercial job that is going o require some EMT to be installed, so we can pull our circuits over to a Junction jox which im going to be feeding outlets and lighting out of it. I got a total of 20 circuits at 20 amps , and im Using 1'1/2 EMT pipe. i also understand that the code says that i can pull up to 61 wires in that conduit and . the part that my boss and i are not very familiar with is the derating part it. we know that we have to derate the wires. But we couldnt find very explanatory in the code book . Could any one explain to me how this part works ?

ASAP ASAP ASAP ASAP ASAP

If the j-box is less than 24 inches from the panel, then you can fill that 1 1/2 EMT up until you can't squeeze another wire into it. Any longer than that, then derating comes into play (well, sometimes - depending on your situation).When you derate for a circuit, what you are doing is reducing the ampacity that a wire can carry. Meaning that one #12 THHN wire has a current carrying ampacity of 25 amps. If you have from four to six of those #12's in a conduit, you have to multiply that 25 amps by .80, or 80%, which now gives you a rating of 20 amps. In your case, with the 61 wires, your multiplier is .35, so you're looking at an ampacity of 8.75. In that case you are going to have to upsize your wire so much it is not economically feasible, or practical. Or run more conduits, which is really what you want to do. Depending on your particular situation, I would probably run 6 or 7 3/4" conduits for my branch circuits, and then set several j-boxes at strategic locations, and go from there. And don't forget to derate for ambient temperature, also. Other than that, it sounds like you bit off more than you can chew.

 

[Volta]

As Rob said, it is in 310.15(B)(2)(a), and also 110.14(C)(a).

If you use 41 #12 THHN cu wires, you can have an EGC, and run a separate neutral each for a 40% derating. You then can have an ampacity of 12 amps per circuit, max load of 12 amps each, protected at 15 amps max.

If you use 20 #10 ungrounded, 7 #10 grounded, and one EGC (3 phase wye), you'll have 21 current-carrying conductors @ 45% derating, allowed as 18 amp (non-linear) loads each.

If you use 20 #10 ungrounded, 10 #10 grounded, and one EGC (single phase), you'll have 20 CCC @ 50% derating, allowed for 20 amp loads.

All before temperature adjustments . . .

As Mr. Wizard said, you won't need to derate if not longer than 24", and you can fit more than usual in such nipple, but fill calc's do still apply. You can use 60% of the area if so. 91 #12's or 57 #10's.
You should be able to start your derating from the 90 deg C column, if THHN, that's what these are based on.

Don't forget 210.4(B) if you share the neutrals.

of course, double check these calc's, they're free!

 

[glene77is]

Keep looking at 310.15, etc.
Right now, after derating, you might have to think about 12 Amp breakers.

Back to the planning board.

 

[infinity]

As Rob said, it is in 310.15(B)(2)(a), and also 110.14(C)(a).

If you use 41 #12 THHN cu wires, you can have an EGC, and run a separate neutral each for a 40% derating. You then can have an ampacity of 12 amps per circuit, max load of 12 amps each, protected at 15 amps max.

Since he said that he has receptacle loads he will not be able to go from a 12 amp adjusted ampacity to 15 amp protection. The next size up rule of 240.4(B) would not apply to multi receptacle circuits.

 

[SEO]

If the j-box is less than 24 inches from the panel, then you can fill that 1 1/2 EMT up until you can't squeeze another wire into it.
Nipples shall be permitted to be filled to 60 percent of their total cross-sectional area. Chapter 9 Tables (4).

 

[jrannis]

My boss and I are doing a small commercial job that is going o require some EMT to be installed, so we can pull our circuits over to a Junction jox which im going to be feeding outlets and lighting out of it. I got a total of 20 circuits at 20 amps , and im Using 1'1/2 EMT pipe. i also understand that the code says that i can pull up to 61 wires in that conduit and . the part that my boss and i are not very familiar with is the derating part it. we know that we have to derate the wires. But we couldnt find very explanatory in the code book . Could any one explain to me how this part works ?

ASAP ASAP ASAP ASAP ASAP

OK how long is the 1-1/2" EMT run?

 

[infinity]

OK how long is the 1-1/2" EMT run?

It sure sounds like the run is more than 24".

 

[Mr. Wizard]

If the j-box is less than 24 inches from the panel, then you can fill that 1 1/2 EMT up until you can't squeeze another wire into it. Nipples shall be permitted to be filled to 60 percent of their total cross-sectional area. Chapter 9 Tables (4).

That is correct. For 1 1/2 EMT, 60% fill is alot of wire!

 

[SEO]

It sure sounds like the run is more than 24".

Jrannis might be looking at 310.15 (A) (2) excp that you used in another post. What if the run was less than 10' to the first box than smaller conduits were branched off pullbox not over three current carring conductors in each and the runs were over 100'? Would that be an exception to the 24" nipple rule?

 

[infinity]

Jrannis might be looking at 310.15 (A) (2) excp that you used in another post. What if the run was less than 10' to the first box than smaller conduits were branched off pullbox not over three current carring conductors in each and the runs were over 100'? Would that be an exception to the 24" nipple rule?

That is possible. I guess we'll need to wait for further details of how he's actually running the conduits. Without the specifics we're all just guessing, but you do bring up a good point.

 

[Volta]

Since he said that he has receptacle loads he will not be able to go from a 12 amp adjusted ampacity to 15 amp protection. The next size up rule of 240.4(B) would not apply to multi receptacle circuits.

Well, since the OP didn't actually use the word receptacles, I didn't think of 240.4(B)(1).

But, of course, you are probably right to interpret "outlets" as "multioutlet branch circuits supplying receptacles" for portable loads.

I should've assumed that at least one of the circuits would feed a convienience receptacle and somthing else.

Good catch.