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thegonagle 10-22-2008 06:57 PM

Quickly rewiring my garage after feeder cut, messed up the planning, need help.
 
Last fall, while running a roto-tiller in my back yard, I hit and damaged the 14-2 UF cable that was supplying my detached garage with lights (and 3 outlets). The cable was only buried about 6-10 inches deep—not very deep, and, as far as I know, shallower than any code ever allowed for direct burial UF cable.

Without knowing much, and wanting to get the lights back on as quickly as possible before winter hit, I rented a 30-inch trencher, and ran a 12-3 (plus ground) UF cable, and an 8-3 (plus ground) UF cable between the house and the garage. The run is about 100-110 feet long.

So what I have running to the garage now is a 12-3, an 8-3, and no ground rod. The 12-3 is temporarily standing in as a replacement for the cable I cut with the tiller (red wire not being used), and the 8-3 is not connected to anything.

I thought I could run a small 40-amp sub-panel off the 8-3 after I upgrade the over-filled panel in my house, and later use the 12-3 for a 3-way switch for an exterior garage light.

I know now that to “do it right,” I would have planned for a 50-60 amp sub-panel (if not more), with a 6-3 UF (if not larger), not 8-3. I was in a hurry just to get the existing garage circuit back on, and didn’t research what should have gone in before the trench was closed. So I have two plans to fix it. What would you do?

Plan A, assuming I drive a ground rod, can I run a 40 amp sub panel off the 8-3? Is there such a thing as a 40 amp subpanel? Is 8-ga just too small to be acceptable as a subpanel feeder? All I was planning on was 2-3 15-20 amp circuits for lighting and outlets, and 30 amps at 240 for a compressor, or possibly a heater.

Or, plan B, I forget the 3-way switch, use the 12-3 to run a shared neutral MWBC to two lighting/outlet circuits, and use the 8-3 for a single 240 volt outlet, up to 40 amps, and run it all off of the (upgraded) main panel in the house?

Plan B seems better now, because I could theoretically run a total of 80 amps if I’ve read the charts correctly (20 on each hot in the 12-3, and 40 in the 8-3).

If I use plan B, would I need a local disconnect for the 240 volt outlet in the garage? Is it acceptable to run a 120-volt MWBC to a detached building? Should I still drive a ground rod even if it all runs off the main panel in the house? If I told you that I threw a RG6 coax (TV) cable and 3 runs of CAT5 down there while the trench was open, would it change the grounding requirements? (Should I put another grounding block on the coax by the garage?)

(Plan C is retrenching, but I don’t want to think about that.)

Thanks for your input,

Joe “TheGonagle”

dSilanskas 10-22-2008 07:17 PM

Quote:

Originally Posted by thegonagle (Post 175499)
Last fall, while running a roto-tiller in my back yard, I hit and damaged the 14-2 UF cable that was supplying my detached garage with lights (and 3 outlets). The cable was only buried about 6-10 inches deep—not very deep, and, as far as I know, shallower than any code ever allowed for direct burial UF cable.

Without knowing much, and wanting to get the lights back on as quickly as possible before winter hit, I rented a 30-inch trencher, and ran a 12-3 (plus ground) UF cable, and an 8-3 (plus ground) UF cable between the house and the garage. The run is about 100-110 feet long.

So what I have running to the garage now is a 12-3, an 8-3, and no ground rod. The 12-3 is temporarily standing in as a replacement for the cable I cut with the tiller (red wire not being used), and the 8-3 is not connected to anything.

I thought I could run a small 40-amp sub-panel off the 8-3 after I upgrade the over-filled panel in my house, and later use the 12-3 for a 3-way switch for an exterior garage light.

I know now that to “do it right,” I would have planned for a 50-60 amp sub-panel (if not more), with a 6-3 UF (if not larger), not 8-3. I was in a hurry just to get the existing garage circuit back on, and didn’t research what should have gone in before the trench was closed. So I have two plans to fix it. What would you do?

Plan A, assuming I drive a ground rod, can I run a 40 amp sub panel off the 8-3? Is there such a thing as a 40 amp subpanel? Is 8-ga just too small to be acceptable as a subpanel feeder? All I was planning on was 2-3 15-20 amp circuits for lighting and outlets, and 30 amps at 240 for a compressor, or possibly a heater.

Or, plan B, I forget the 3-way switch, use the 12-3 to run a shared neutral MWBC to two lighting/outlet circuits, and use the 8-3 for a single 240 volt outlet, up to 40 amps, and run it all off of the (upgraded) main panel in the house?

Plan B seems better now, because I could theoretically run a total of 80 amps if I’ve read the charts correctly (20 on each hot in the 12-3, and 40 in the 8-3).

If I use plan B, would I need a local disconnect for the 240 volt outlet in the garage? Is it acceptable to run a 120-volt MWBC to a detached building? Should I still drive a ground rod even if it all runs off the main panel in the house? If I told you that I threw a RG6 coax (TV) cable and 3 runs of CAT5 down there while the trench was open, would it change the grounding requirements? (Should I put another grounding block on the coax by the garage?)

(Plan C is retrenching, but I don’t want to think about that.)

Thanks for your input,

Joe “TheGonagle”

Go to home depot and get a eight or ten circuit panel and put a double pole 40 in and use that as the main use the 8/3. Sink a ground rod outside the shed

InPhase277 10-22-2008 08:25 PM

Plan A is fine and probably your best bet. There is nothing wrong with a 40 A subfeed except that the code requires the disconnect to be rated at 60 amps. The solution for this would be to feed the 8-3 from a 40 A breaker in the house panel, but use a 60 A breaker as the main in the garage panel. You can use any size panel that you want as the sub.

And of course, keep grounds and neutrals separate in the subpanel, and be sure to bond the panel can with whatever means is included in the kit that comes with the panel. Drive your ground rods and connect them to the ground bar.

J. V. 10-23-2008 11:05 AM

You are not allowed by the NEC to have more than one (1) branch circuit, feeder or service entering a building on your property. If you are going to install the sub panel, of course you can keep the 8/3, but the 12/3 must go.

Article: 225.30

InPhase277 10-23-2008 11:25 AM

Quote:

Originally Posted by J. V. (Post 175810)
You are not allowed by the NEC to have more than one (1) branch circuit, feeder or service entering a building on your property. If you are going to install the sub panel, of course you can keep the 8/3, but the 12/3 must go.

Article: 225.30

He did say that the 12-3 would be used as a 3 way switch loop. That is totally legal.

J. V. 10-23-2008 01:02 PM

Quote:

Originally Posted by InPhase277 (Post 175827)
He did say that the 12-3 would be used as a 3 way switch loop. That is totally legal.

You bring up an excellent point. Regardless of where the switch loop is getting it's power from, you still have hot wires in both structures even when the power is shut off in one of them. That is the purpose of 225.30, to prevent this. Can you shed some more light on this subject. Anyone?

InPhase277 10-23-2008 01:34 PM

Quote:

Originally Posted by J. V. (Post 175877)
You bring up an excellent point. Regardless of where the switch loop is getting it's power from, you still have hot wires in both structures even when the power is shut off in one of them. That is the purpose of 225.30, to prevent this. Can you shed some more light on this subject. Anyone?

Be happy to. Check out the article you reference: 225.30. Specifically, look at D.

J. V. 10-23-2008 02:05 PM

Quote:

Originally Posted by InPhase277 (Post 175890)
Be happy to. Check out the article you reference: 225.30. Specifically, look at D.

Got it. Thanks.

thegonagle 10-23-2008 04:08 PM

So, I pretty much have to go with my original plan, not "plan B," because I can only run one feeder per structure, correct? (That's OK, it makes sense. I'll feed it off a 40-amp breaker in the main.)

And regarding the 3-way switch loop, I take it that it's legal (I'd hope so, I got the idea from the house I grew up in), but it should get power from the garage panel, not the house panel. That way, if I shut down the garage subpanel (the 8-3 feeder), the 3-way switch loop is also shut down. Is that correct? (Anything else from 225.30 that I need to know?)

A couple more questions regarding proper grounding of the sub:

1) Should I pound 2 ground rods, 6 feet apart, or does that apply to the main service only? (Or do I have to test the first one, and then decide whether to drive a second, and how would I test that?)

2) What gauge bare/green wire should I use for the ground rod(s)?

3) I put a TV cable down there, too, about 18 inches down, so about a foot away from the electrical. Should I use a ground block where the coax enters the garage and ground it to the rest of the system? (There's already one coax ground block grounding the cable before it goes into the house.)

Thanks again, everybody! :)

InPhase277 10-23-2008 04:34 PM

Quote:

Originally Posted by thegonagle (Post 175943)
So, I pretty much have to go with my original plan, not "plan B," because I can only run one feeder per structure, correct? (That's OK, it makes sense. I'll feed it off a 40-amp breaker in the main.)

Sounds good, just don't forget that the main in the sub has to be 60 amps.

Quote:

And regarding the 3-way switch loop, I take it that it's legal (I'd hope so, I got the idea from the house I grew up in), but it should get power from the garage panel, not the house panel. That way, if I shut down the garage subpanel (the 8-3 feeder), the 3-way switch loop is also shut down. Is that correct? (Anything else from 225.30 that I need to know?)
Yes. 225.30 states that only one branch circuit or feeder can power a remote building. But 225.30(D) states that special circuits can also be present. One of these being a circuit to control outside lighting from multiple locations.

Quote:

A couple more questions regarding proper grounding of the sub:

1) Should I pound 2 ground rods, 6 feet apart, or does that apply to the main service only? (Or do I have to test the first one, and then decide whether to drive a second, and how would I test that?)

2) What gauge bare/green wire should I use for the ground rod(s)?

3) I put a TV cable down there, too, about 18 inches down, so about a foot away from the electrical. Should I use a ground block where the coax enters the garage and ground it to the rest of the system? (There's already one coax ground block grounding the cable before it goes into the house.)

Thanks again, everybody! :)
Yes, drive two rods, and connect them together and to the ground bar in the sub with #8 copper. And yes, ground the coax again at the building. This is easy enough. Just use a split bolt connector to secure a #10 to the #8 from the ground rods.

thegonagle 10-23-2008 04:55 PM

Awesome. You guys have been a great help. I thought I had a real clusterf--- going on, and my greatest fear was not being able to use any of what I put in the ground the way I had intended. Now I know exactly what needs to be done. Thanks dS, J.V., and InPhase.


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