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.
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)
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 12/21/0611:07 AM12/21/0611:07 AM
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.
"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.
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?
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 12/22/0612:22 AM12/22/0612:22 AM
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.