Grounding question


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Old 01-04-04, 05:28 AM
J
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Grounding question

I am helping a friend build in work area inside his shop building at his home. We have a 15x20 area that is enclosed and insulated. The shop has a separate drop and meter base, not sure if its 200 or 250A. We will be running electrical soon and I have a question regarding grouding conductors. I have done quite a bit of electrical work although mostly residential but was trained on commercial in high school and have done a fair amount of that as well. We will need 2 110V 20A circuits, 1 220V 20A circuit, and 2 220V 50A circuits. My current plan is to run all conductors in a single run of EMT, appropriately sized of course, to a large j-box at the work area and branch off from there. My reasoning here of for a clean install.

1. I have seen grounding conductors run in EMT at times but recall from my schooling that they are not required as that need is met by the conduit. Is this still the case?

2. Can I apply the same logic to the 220V circuits as well?

3. Although I can't recall seeing circuits mixed in conduit as I am planning nor do I recall being instructed that this can or cannot be done I still must ask. Is this acceptable.

Any other input would be greatly appreciated.

Thanks,

Jester
 
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Old 01-04-04, 08:51 AM
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You can do as you intend.
You an use the conduit as the ground as long as all the connectors are made up tight. I would still run a ground though.

When you run multiple circuits in a conduit as you want you size the equipment ground to the largest over current device. In your case this would be the 50amp circuit so a #10 ground is fine.

You will have to use a ground bar in the box at the end unless you want to make a large wire nut splice with all the grounds. You'll have 3-#10 and 3-#12, not really too bad with a big blue wire nut. The box will be grounded by the conduit anyway.

Another consideration is conductor amperage derating. With more than 3 current carrying conductors in the pipe you need to derate the wire's capacity. With the 10 conductors you are running you need to derate each by 50%. This may be a factor in how you work this project. If you use a multi-wire circuit for the two 120v. circuit (2 hots sharing a neutral) you drop the current carrying conductors to 9 and the derating factor goes to 70%. This will at least let you run #6 for the 50amp circuit.
 
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Old 01-05-04, 10:24 AM
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So I can use the ocnduit as a ground, correct?

As for derating, I must have been asleep that day in class. For example, if I run 12AWG for my 110 circuits I can only count on 14 amps unless I run a 10AWG right?

To share a neutral on the 110 circuits, do I need to make sure that the hots come from both legs or can they be on the same leg in the panel?

Thanks
 
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Old 01-05-04, 10:45 AM
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A multiwire circuit must come from both legs of the 220 power. This is the onmly reason you can get away with a single neutral the same size as the hot wires.

There are several other things as well.

You should use two adjacent slots in the panel. If the two hot lines go to each half of a duplex outlet then the breaker handles must be tied together. Many people recommend tieing the handles together anyway, but it is not required unless the two hots end up on the same device.

All neutral connections that do not terminate in a box must be pigtailed. (You cannot rely on the feed through in a duplex outlet to continue the neutral.)

GFCI protection on a multiwire circuit needs to be done either at each outlet, or at the panel, or the multiwire circuit needs to be split into 2 two wire circuits, each of which can be protected by a GFCI outlet.
 
 

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