Detached garage; several questions.


Old 11-25-05, 07:34 PM
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Detached garage; several questions.

I am in the process of wiring a 1200 sq-ft detached garage that is approximately 100ft from my home's service entrance. I have basically completed wiring the garage interior and only have to lay the feeder to the house's service entrance to finish.

The house has single-phase 3-wire service. It has an old Zinsco brand load center/meter combo box (Cat. No. TRP-350L) with one 150A breaker serving the house (which has a 200A panel!) and a separate 30A breaker serving the heat pump. Pictured here:
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The garage's subpanel is a 100A Square-D panel with 20 sockets and a 100A main. Pictured here:
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Is there any possibility of both the house and the garage sharing the same 150A circuit breaker shown here?:
<a href=></a> (Big one on the left).

One thing that makes me think "no" is a sign on the box that says "CAUTION Do not interconnect the outputs of different class 2 circuits". But this sounds to me more like it's warning against combining two separate service circuits:
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I'm not sure what a class 2 circuit is.

If this is not a possibility, I assume it would be OK to add another breaker (60A+) for the garage. I think I have room for a 1-1/2" breaker if I remove the unused (red) breaker:
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The inspector wants me to bury a 4-conductor feeder. I take this to mean that he wants me to use the ground at the service entrance rather than add a grounding rod at the garage. Would one ever add a grounding rod at the garage too and connect the ground at the service entrance to the new ground at the garage (and to the subpanel in the garage)?

I want to be sure of another thing. I originally thought that I needed an external disconnect for the garage. I now understand that the garage subpanel's 100A main breaker (inside) will qualify as my disconnect. Does anyone see a problem with this? My current plan is to just run PVC conduit from the ground directly into the garage and connect to the panel.

I'm pretty confident about my plans to lay the feeder itself, but just in case someone sees a red flag: I plan to lay four 2/0 aluminum direct-burial conductors (or a bundle if it's more cost-effective.) 18" deep. About 6" above that, I'll lay 1" conduit for water and 2" conduit for Ethernet, phone, etc. Another 6" up, I'll lay a "buried cable" safety ribbon.

Thanks for any advice!
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Old 11-26-05, 12:57 PM
Join Date: Apr 2004
Location: Ontario Canada
Posts: 1,767
You cannot double lug with the 1050A there. You need to add a 60A breaker.

You need to feed a 4 wire cable from the service, plus install a ground rod.

IMO, you should really replace the old Zinsco with new modern equipment, as Zinco is as troublesome as ond FPE gear.
Old 11-26-05, 05:45 PM
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That's probably a good idea. I'll do some pricing. It's ironic that you compare it to FPE. Guess what's in the house. Ugh!

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