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Grounding #73245
12/20/06 07:54 PM
12/20/06 07:54 PM
K
kyelectric  Offline OP
Member
Joined: Aug 2005
Posts: 64
I am running a bunch of branch circuits through 2" EMT conduit to a large pull box. I always run all of the grounds for every circuit. But, Is there a time you can pull a ground that is the same size as the largest ungrounded conductor and install a ground bar in the juction box and terminate the grounds there? As long as I have one main ground going back to the panel is there a problem? Thanks.

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Re: Grounding #73246
12/20/06 08:27 PM
12/20/06 08:27 PM
electure  Offline

Member
Joined: Dec 2000
Posts: 4,274
Fullerton, CA USA
Yes, and that time is every time.

I hope that you are planning on derating the conductors on your branch circuits per Table 310.15(B)(2)a, and don't forget that the equipment grounding conductor will have to be increased proportionatly in size as well per 250.122(B)

Re: Grounding #73247
12/20/06 08:30 PM
12/20/06 08:30 PM
I
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
You can do that.

Quote
250.122(C) Multiple Circuits. Where a single equipment grounding conductor is run with multiple circuits in the same raceway or cable, it shall be sized for the largest overcurrent device protecting conductors in the raceway or cable.


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Re: Grounding #73248
12/21/06 11:07 AM
12/21/06 11:07 AM
K
kyelectric  Offline OP
Member
Joined: Aug 2005
Posts: 64
Electure, thanks for the input. I will derate the conductors accordingly. Iwire, can I use any grouding bar and install it in the pull box? The largest OCP device will be 30 amps with #10 wire. I was going to pull 1 or 2 #10 grounds and attach them to a ground bar in the pull box. There I will also attach several other branch circuit grounds. Thanks.

Re: Grounding #73249
12/21/06 01:16 PM
12/21/06 01:16 PM
electure  Offline

Member
Joined: Dec 2000
Posts: 4,274
Fullerton, CA USA
"The largest OCP device will be 30 amps with #10 wire."
How many current carrying conductors do you plan on having in this 2" conduit? Between just 10 and 20, you must derate to 50%, which would make the maximum ampacity of your #10 THHN 20 Amps. If you've got visions of running a whole panel's worth of wire through a 2" conduit longer than 24", forget about having #14, #12, or possibly even #10 as part of the equation.

"1 or 2 #10 grounds"
Just run 1 properly sized conductor, or simply mount the ground bar in the box, and run none at all.

Re: Grounding #73250
12/21/06 04:32 PM
12/21/06 04:32 PM
K
kyelectric  Offline OP
Member
Joined: Aug 2005
Posts: 64
There will only be 8 current carrying conductors in the 2" EMT. The rest will be neutrals and 1 properly sized ground wire. When you say "simply mount the ground bar in the box, and run none at all." Are you suggesting that the EMT will be the ground since it is grounded in the subpanel with a grounding bushing?

Re: Grounding #73251
12/21/06 07:36 PM
12/21/06 07:36 PM
J
john p  Offline
Member
Joined: Nov 2006
Posts: 32
Bemidji,MN.USA
Neutrals are also counted as current carrying wires for derating purposes.

Hope that helps.

John

Re: Grounding #73252
12/21/06 07:39 PM
12/21/06 07:39 PM
I
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Quote
Neutrals are also counted as current carrying wires for derating purposes.


Yes and no.

If the neutral is truly a neutral and only carries the unbalanced current from a multiwire branch circuit you do not have to count it.


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Re: Grounding #73253
12/21/06 08:30 PM
12/21/06 08:30 PM
electure  Offline

Member
Joined: Dec 2000
Posts: 4,274
Fullerton, CA USA
Sure, EMT is recognized as a grounding conductor, and if installed properly (with any paint under the TIGHT locknuts removed) a grounding bushing isn't required in this case at all, even at the subpanel.
You must remove any paint under the ground bar anyway, and not fasten it with teks screws or sheet metal screws.

I still don't quite understand why you have a 2" EMT planned if you've got only 8 current carrying conductors, the largest being a #10 (actually a #8, if you'll look below). 16-#10s will physically fit in a 1" EMT.

With only 7 to 9 current carrying carrying conductors, your derated conductor ampacity for #10 THHN will be 70% of it's listed ampacity (40A), or 28 amps.

You might want to consider splitting the circuits up and running (2)3/4" EMTs or (1)3/4" and (1)1/2" instead and saving yourself some time, work, and a bunch of money.

Re: Grounding #73254
12/22/06 12:22 AM
12/22/06 12:22 AM
K
kyelectric  Offline OP
Member
Joined: Aug 2005
Posts: 64
2" EMT is what the electrical engineer at the plant called for. He said, "for future expansion". So, it's not costing me any extra money. Some people only look at the amount of conductors you can put inside of conduit and don't consider the derating factor.


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