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Old 02-15-2012, 12:43 PM   #1
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Can I run several circuits through the same conduit?


I need to bring five individual circuits into my bathroom/dressing room addition. I'd like to run THHN/THWN from the outdoor breaker panel, through conduit and into a junction box in the attic where everything will switch over to NM.

I'm trying to get a handle on how to most efficiently run the wire through conduit to minimize the number of conduit I need, and cut down on wire usage.

The circuits break down as follows:

-20amp 12ga for bathroom outlets (GFCI at outlet)
-20amp 12ga for whirlpool tub motor (GFCI at outlet)
-20amp 12ga for electric fireplace
-15amp 14ga for bathroom ceiling lighting
-15amp 14ga for dressing room ceiling lighting, outlets and smoke detectors (on AFCI breaker)

I am aware of the restrictions on the number of wires you may run in a single conduit (based on size). I am having trouble finding answers on the following:

1. Can I share a single ground wire between all circuits run through a particular conduit?
2. Can I run multiple circuits in one conduit?
3. Is it ok to run a hot and neutral wire for each of those circuits through that conduit? For instance, I have three 20amp circuits - Can I then run all three through one conduit with 3 hot and three neutral wires and one ground wire (tying it in to all NM at the junction)?

My preference would be to run 2 conduits - One with the 20amp circuits, the other with the 15amp circuits, keeping in mind that one of the 15 amp circuits will be on an AFCI breaker (to comply with smoke detector rules).

Thank you.

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Old 02-15-2012, 12:47 PM   #2
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Can I run several circuits through the same conduit?


Additionally - Wire colors... When running multiple circuits in one conduit, can I just use three white, three black and the ground? Or do I need to use different color wires to denote the different circuits? For instance, a black, red and blue wire for the hots?

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Old 02-15-2012, 01:00 PM   #3
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Can I run several circuits through the same conduit?


1. Yes. Ground must be sized to largest circuit. In this case #12.
2. Yes
3.Yes you can.

You can use all black and white + green ground or you can use different colour hots + white and green.

I think I would probably just put the bathroom light on the bathroom 20 amp circuit and eliminate one 15 amp circuit.
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Old 02-15-2012, 01:15 PM   #4
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Can I run several circuits through the same conduit?


Quote:
Originally Posted by JeepNick View Post
I need to bring five individual circuits into my bathroom/dressing room addition. I'd like to run THHN/THWN from the outdoor breaker panel, through conduit and into a junction box in the attic where everything will switch over to NM.

I'm trying to get a handle on how to most efficiently run the wire through conduit to minimize the number of conduit I need, and cut down on wire usage.

The circuits break down as follows:

-20amp 12ga for bathroom outlets (GFCI at outlet)
-20amp 12ga for whirlpool tub motor (GFCI at outlet)
-20amp 12ga for electric fireplace
-15amp 14ga for bathroom ceiling lighting
-15amp 14ga for dressing room ceiling lighting, outlets and smoke detectors (on AFCI breaker)

I am aware of the restrictions on the number of wires you may run in a single conduit (based on size). I am having trouble finding answers on the following:

1. Can I share a single ground wire between all circuits run through a particular conduit?
2. Can I run multiple circuits in one conduit?
3. Is it ok to run a hot and neutral wire for each of those circuits through that conduit? For instance, I have three 20amp circuits - Can I then run all three through one conduit with 3 hot and three neutral wires and one ground wire (tying it in to all NM at the junction)?

My preference would be to run 2 conduits - One with the 20amp circuits, the other with the 15amp circuits, keeping in mind that one of the 15 amp circuits will be on an AFCI breaker (to comply with smoke detector rules).

Thank you.
1. You can share a single ground but it must be sized for the largest circuit running in the conduit.
2. Yes it is ok.
3. I believe in a 1/2" conduit you are able to run 9 - 12g wires. (but you must calculate derating of the wires, which may cause you to upsize the gauge of wire used) I can see if i can find my chart and put it on here.

If you are using EMT you are allowed to use the conduit itself as the grounding conductor, but as you leave the junction box on either size you must tie the ground wire to the conduit so that it will travel back to the grounding bar.
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Old 02-15-2012, 01:17 PM   #5
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Can I run several circuits through the same conduit?


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Originally Posted by joed View Post
I think I would probably just put the bathroom light on the bathroom 20 amp circuit and eliminate one 15 amp circuit.
Thank you. This is a good idea - I thought I couldn't do that, but after going back and reading the code again, it turns out I can.
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Old 02-15-2012, 01:23 PM   #6
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Can I run several circuits through the same conduit?


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Originally Posted by JeepNick View Post
Thank you. This is a good idea - I thought I couldn't do that, but after going back and reading the code again, it turns out I can.
It depends on where you live. In Canada, residential lighting cannot be protected by overcurrent devices rated at anything above 15 A.
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Old 02-15-2012, 01:29 PM   #7
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Can I run several circuits through the same conduit?


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3. I believe in a 1/2" conduit you are able to run 9 - 12g wires. (but you must calculate derating of the wires, which may cause you to upsize the gauge of wire used) I can see if i can find my chart and put it on here.
Thank you.

I want to avoid derating the wires. My local code states that you can have up to three current carrying conductors in a conduit without making proximity adjustments to the ampacity.

I'd rather run two conduits than have to make adjustments or upsize my wire.
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Old 02-15-2012, 03:01 PM   #8
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Can I run several circuits through the same conduit?


Remember that each current circuit has 2 current carrying conductors. So unless you want to run a separate conduit for each run, you're going to need to derate the conductors. Go ahead and do the derating calculations. I suspect you'll find that if you use 90c wire you don't need to upsize the wires if you use 2 conduits.
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Old 02-15-2012, 05:39 PM   #9
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Can I run several circuits through the same conduit?


Not sure why you'd want to run 2 sets of conduit if you are ok with one. Using EMT eliminates the ground conductor. If you configue a pair of the circuits as MWBC then they can share a neutral wire dropping another wire in the fill calculations.

so you'd need 9 wires in the conduit

MWBC #1:
2wires -20amp 12ga for bathroom outlets (GFCI at outlet)
1wire -20amp 12ga for whirlpool tub motor (GFCI at outlet)


2wires -20amp 12ga for electric fireplace (should be an individual branch circuit)


2wires -15amp 14ga for bathroom ceiling lighting

2wires -15amp 14ga for dressing room ceiling lighting, outlets and smoke detectors (on AFCI breaker)

So nine (5 #12, 4 #14) wires/conductors in total. That should fit in 1/2" EMT (capacity of 9 #12, or 12 #14), you'll have to do the calc's to be sure. If you are worried go with 3/4" EMT and have a safety margin plus room for future upgrades with a home run conduit line back to the panel....

I was wondering if you could put the 15A circuits onto a MWBC and drop another neutral wire and put an AFCI receptacle in the first spot and feed the rest of the branch. I guess AFCI receptacles are pretty rare so maybe an idea but hard to implement.
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Old 02-15-2012, 06:36 PM   #10
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Can I run several circuits through the same conduit?


You can have up to nine current carrying conductors (CCC's), sized #14, #12 or #10) before you have to even think about derating. Neutrals are CCC's, grounds are not.

Use one conduit. Run one ground sized for the largest circuit.
Multi-wire circuits (MWBC) would be even better since the neutral of a MWBC does not count towards derating.
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Old 02-15-2012, 06:36 PM   #11
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Can I run several circuits through the same conduit?


Quote:
Originally Posted by hawkeye11 View Post
It depends on where you live. In Canada, residential lighting cannot be protected by overcurrent devices rated at anything above 15 A.
That's true. But the OP is in AZ (Arizona) so different rules apply. We also don't need 20amp dedicated circuits for our bathrooms. They do in USA.
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Old 02-15-2012, 07:29 PM   #12
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Can I run several circuits through the same conduit?


In case you do not want to use multiwire branch circuits......to be able to use one conduit.......

How long is your conduit run going to be before your transition to the nm cable at the junction box? Will it be more than 10 feet?

There is an exception that might allow you to use the higher ampacity of the nm since the deration for 10 ccc's in conduit would reduce your ampacity to below 20 amps allowable for the #12 awg 20 amp branch circuits and below 15 for the 14 awg 15 amp circuits.. Your nm probably should have an adjustment for ambient due to the high attic temps in Arizona. However I can't see that lowering your ampacity below what the nm is rated for at 60C.

10 ccc's in conduit has a reduction multiple of .50 that puts your 12 awg at 15 amps and your 14 awg at 12.5 amps. You can use the higher ampacity of the nm if the lower ampacity of the wires in conduit is not over 10 feet long and not longer than 10% of the higher ampacity length.
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Old 02-15-2012, 08:55 PM   #13
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Can I run several circuits through the same conduit?


There's also a maximum conduit fill size to be aware of. There are various NEC requirements here but the fun starts at 300.17.
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Old 02-16-2012, 02:57 PM   #14
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Can I run several circuits through the same conduit?


Lots to take in... The conduit run would be roughly 30 feet from breaker box to NM junction.

Local code book says the following about derating wires in conduit:

4-6 wires 80%
7-9 wires 70%

Ampacities Table lists:

THHN 90c wire at 25amp for 14awg and 30amp for 12awg.

If I ran two conduits with the 15amp in one and 20 amp circuits in the other, (4 and 6 CCCs) I would derate the 14awg (15amp circuits) 90c wire from 25amps to 20amps (80%) and the 12awg (20amp circuits) 90c wire from 30amps to 24amps.

Does that make sense? Am I ok to do it that way? Do I need to do any adjustments for ambient temperatures in AZ being hotter than normal? The conduit will be in full shade 100% of the time.

I'm not crazy about doing a MCBW. My breaker box has one side completely full and the other has the 5 open slots for the circuits I want to add. My understanding of MCBW is that I would have to have the breakers in the MCBW on opposite sides of each other so the neutral wire would "phase" properly...if thats the right word. I'd rather not have to move any breakers from one side to the other, especially since I don't know anything about how the rest of the house is wired....other than its old. Service panel was upgraded about 4 years ago by a licensed electrician. I had nothing to do with it.

Last edited by JeepNick; 02-16-2012 at 03:01 PM.
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Old 02-16-2012, 03:16 PM   #15
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Can I run several circuits through the same conduit?


Most panels have alternating buss arranged ABAB in a vertical manner. A properly wired MWBC would have hots on both A and B.

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