Conduit fill

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wireday

Senior Member
Location
New England
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Master electrician
I would like to add a couple conductors to an existing 1/2 EMT run. The run currently has 2 #12 conductors and a #12 ground, 2 #10 conductors. I would like to add 2 more #12s, Im not sure of figuring the fill with two different size conductors.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
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Retired Electrical Contractor
Use table 4 and 5 from chapter 9 to do the calculation

12 THwn = .0133 sq. in
10 Thwn = .0211 sq.in

5x .0133 + 2 x .0211 = .0665 + .0422 = .1087 sq. in

Table 4 for emt shows 1/2" emt with over 2 wires(40%) at .122 sq.in

since .1087 is small than .122 then you are compliant. A long pull may not be so easy
 

infinity

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Location
New Jersey
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Journeyman Electrician
Good catch. Since it is emt then you could just remove the equipment grounding conductor.

Would you be required to remove it? Why can't you use the #12 for the circuit with the #12 conductors and use the EMT for the #10's circuit?
 

Dennis Alwon

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Location
Chapel Hill, NC
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Would you be required to remove it? Why can't you use the #12 for the circuit with the #12 conductors and use the EMT for the #10's circuit?

Trevor I don't know why but I believe it is not compliant. There does not seem to be another option but IMO, there should be

250.122(C) Multiple Circuits. Where a single equipment grounding
conductor is run with multiple circuits in the same raceway,
cable, or cable tray, it shall be sized for the largest overcurrent
device protecting conductors in the raceway, cable, or cable
tray. Equipment grounding conductors installed in cable trays
shall meet the minimum requirements of 392.10(B)(1)(c).
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
I don't see 250.122(C) as precluding using the EMT as the EGC for one circuit and using the wire type EGC for the other circuit(s). That would be multiple EGCs, so 250.122(C) doesn't apply.

Cheers, Wayne
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Actually wouldn't you be using the #12 and the conduit as the EGC for both circuits? I'm sure you have the #12 bonded to the boxes at both ends which puts the #12 and the conduit in parallel.

Like was said, you really don't need to use an separate EGC here at all, but many of us do because you don't want to rely just on the conduit. Though there is no reason not to, it's a matter of choice. So you are going to have to make up your mind. If you want a separate EGC I would remove the #12 and replace it with a #10 because a separate EGC says you aren't relying on the conduit. But if doing so exceeds the allowable fill then just remove the #12. Will make pulling easier anyway.

-Hal
 

jmellc

Senior Member
Location
Durham, NC
Occupation
Facility Maintenance Tech. Licensed Electrician
Do they still make that stuff? Anyone still use it?

Yes, they still make it and some guys still use it.

I just talked with the boss about 77 the other day. He still loves it, says it's the best for a long hard pull. I've had better luck with Aqua Gel and it is much easier to clean up. 77 looks like puke & is hard to clean up. It gunks pipe up too & makes future removal of wire much harder.
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
Actually wouldn't you be using the #12 and the conduit as the EGC for both circuits? I'm sure you have the #12 bonded to the boxes at both ends which puts the #12 and the conduit in parallel.

Like was said, you really don't need to use an separate EGC here at all, but many of us do because you don't want to rely just on the conduit. Though there is no reason not to, it's a matter of choice. So you are going to have to make up your mind. If you want a separate EGC I would remove the #12 and replace it with a #10 because a separate EGC says you aren't relying on the conduit. But if doing so exceeds the allowable fill then just remove the #12. Will make pulling easier anyway.

-Hal

I would use the green as a pull wire for my new conductors.
 
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