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Old 08-30-2013, 12:51 PM   #1
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conduit fill question for the pros


given a section of EMT containing 2 hots, a neutral, and a bare ground wire.

For the purposes of determining conduit fill, how many current carrying conductors are there? Is the answer three or is the answer 4? I'm assuming that it is four but wanted to be sure since the ground isn't necessarily a current carrying conductor.

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Old 08-30-2013, 01:25 PM   #2
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conduit fill question for the pros


Conduit or box fill is not based on current carrying conductors but the actual conductor count. you have 4 conductors.

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Old 08-30-2013, 01:30 PM   #3
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conduit fill question for the pros


Conduit fill has to do with how many wires and not current carrying conductors.

Derating is what happens with the ccc. in conduit.
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Old 08-30-2013, 01:44 PM   #4
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The echo is really bad today.
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Old 08-30-2013, 02:01 PM   #5
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The echo is really bad today.
I had my response typed up then got a phone call, otherwise I would have never responded.
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Old 08-30-2013, 02:22 PM   #6
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conduit fill question for the pros


You are confusing conduit fill(number of wires that will physically fit in a conduit) with wire derating(number wire before you need to go to a larger gauge for the same current). Conduit fill counts all the wires. Wire derating counts only the current carrying conductors.
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Old 08-30-2013, 02:33 PM   #7
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conduit fill question for the pros


My apologies, I should have asked it from a derating perspective since my question is precisely to that point. In my defense, the two are inter-related in my case.

Fill is cross sectional based on number/size of the conductors and currently I'm good to go with 3 #10 THHN, a bare #10, and 1 #12 THHN in half inch EMT. I want to add conductors however and will still pass from a conduit fill perspective if I add two #12 THHN conductors. However, I'll have to go to larger conductors to handle the larger derating factors if the ground wire counts as a current carrying conductor since the total number will now be 7. However, if I have to go to larger conductors, I'll fail on conduit fill.


What's the answer, does that ground wire count as a current carrying conductor?

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Old 08-30-2013, 02:38 PM   #8
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conduit fill question for the pros


From post #2

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Conduit or box fill is not based on current carrying conductors but the actual conductor count. you have 4 conductors.
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Old 08-30-2013, 02:56 PM   #9
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conduit fill question for the pros


Why a single #12?
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Old 08-30-2013, 03:53 PM   #10
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conduit fill question for the pros


It appears that a 20 amp branch circuit was moved to the 30 Amp sub panel that sits directly below the main panel. The 1/2" conduit in question is only about 2" long and extends from the bottom of the main panel to the top of the sub panel just below.

The neutral for the 20A branch circuit was left in place on the main panel; thus only 1 #12 wire was used. It was done because there was originally a tandem breaker in the main panel which doesn't allow them. I thought it was a bit fishy but couldn't think of any code related issues.
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Old 08-30-2013, 03:56 PM   #11
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conduit fill question for the pros


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From post #2
Thanks. Looks like I need to go up to 3/4 EMT then.
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Old 08-30-2013, 04:14 PM   #12
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conduit fill question for the pros


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does that ground wire count as a current carrying conductor?
No, the grounding conductor doesn't count.

Also, you don't have to worry about derating until you have fill of more than 9 CCC's.

Table 310.15(B)(2) @ 7-9 ccc's calls for derating to 70%.

Looking at table 310.16 for 14,12 & 10 allowable ampacities are 25,30, & 40.

These ampacities are for derating purposes only.

So, for #12 @ 30 amps times .7=21 amps and #10 @ 40 amps times .7=28 amps.
Notice #12 ends up @ 21 amps and #10 ends up at 28.

Now, let's go to 240.4(D) says that overcurrent protection for 14, 12, and 10 shall not exceed 15,20, and 30 amps.

So, the #12's OCPD cannot exceed 20 even though it's 21. However, the #10 @ 28 amps can be put on a 30 amp breaker because the code allows you to go to the next higher standard breaker size as long as it's not over 30 amps.

There are also exceptions to the above conductor OCPD's in cases such as motors, HVAC equipment, and a variety of other applications.

If you could tell us what each conductor you listed was, it would be easier to determine amount of ccc's because, the grounded conductor doesn't always count as a ccc.

Sorry for the long explanation but this an example of the we have to go through on a day to day basis.

So when people say "why do you charge this much to do this, all you have to do is hook up a couple wires, how hard can that be"?
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Old 08-30-2013, 04:22 PM   #13
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conduit fill question for the pros


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The 1/2" conduit in question is only about 2" long
Conductor derating doesn't apply to conductors in a nipple less than 24" however, conductor fill does.
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Old 08-30-2013, 04:30 PM   #14
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conduit fill question for the pros


Believe me, I know exactly how much you guys do. Took me about a week to figure out how to do a mini-split install a few years back....

I thought I read a 240.4 provision that nixed rounding up to a 30A OCPD in my case though because it protects a sub-panel feeder. I'll go check through it again.

Anyway, the conductors are:

3 #10 THHN: hot/hot/neutral for sub panel
1 #10 bare: ground for subpanel
1 #12 THHN: hot for 20A branch circuit extended from main panel directly above (see earlier post).

proposed:

2 #12 THHN: move a 240V 20A baseboard heating branch circuit from main panel to sub panel.
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Old 08-30-2013, 04:33 PM   #15
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Conductor derating doesn't apply to conductors in a nipple less than 24" however, conductor fill does.
Really? That's perfect! Do you know where this is cited? I want to have my ducks in a row for the inspector when I move the circuit.

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