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Electrical Wiring

Service Wiring to Sub Panel

16 years ago

I need advice on how to deal with ground & neutral at & to my new detached garage sub-panel. I have a modular home (similar to mobile)on a steel chasis with a 100 amp service panel (with no further space/access to it through the conduit). The factory bonded the house panel grnd.to the steel frame, I extended this down to an approved buried ground plate. I brought a 200 amp underground service into home, it pops up at o/s wall to meter and then down again into my crawl space. Between meter & panel I interupted the wire through a 200 amp disconnect and then up to my house panel. This service wire is 2/2 Al(inspected & passed in 1992). I now want to connect into this disconnect with left over 2/2 Al and through a fused 100 disconnect and underground through buried conduit to my 100 amp garage panel (that has 100 amp main breaker)How do I treat ground and neutral. Drive new ground rods and ground this sub-panel, and leave grnd/neutral bonded in it. Or do I extend existing ground to garage sub-panel, and find a big neutral from house panel, and remove bond in sub-panel between neutral and ground?? Appreciate help and alternatives. I think I should treat sub-panel as equal to main house panel, and drive new ground rods etc.

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Comments (7)

jmorrow
16 years ago
you MUST drive rod @ the garage. you can run either 3-wire (hot, hot, neutral) or 4-wire (hot, hot, neutral, ground). if 3-wire, bond grounds & neutrals @ subpanel. if 4-wire, keep them seperated and make absolutely sure that you connect ground rod to ground bar.
jimmyleon
16 years ago
Jmorrow gives you great advice. I would run three wire cable instead four and you will not have to seperate the neutrals and grounds by doing that. I would put at least 2 ground rods at the second building, of course attached to your sub panel in the second building, at least about 7 feet apart with continuous run of the ground wire to the last ground rod.
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In the main panel the neutral and ground of the 6/2 are connected to the neutral or ground bus. That's because the neutral and ground are bonded in the main panel. In the sub panel, the neutral goes to only the neutral bus, and the ground goes only to the ground lug. The neutral and ground are not bonded in the sub panel. If your sub panel comes with the bond between neutral and ground installed, remove the bond before installation.
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spencer_electrician
16 years ago
3 wire will work unless there is or EVER will be any other connection between the two buildings. Such as plumbing, cable tv, phone, data, light switch. If there is any other connection, it must be a 4 wire. I recomend a 4 wire anyway, unless it is a penny pinching situation. The ground wire doesn't have to be as large as the neutral conductor any way. A 4 wire connection has its advantages.
cobraguy
16 years ago
Does the ground rod at the garage need to be connected to the house ground rod? Or is this not needed because he doesn't have a true sub panel in the garage because he's tapping the supply in front of the main panel?
jmorrow
16 years ago
cobraguy,
the ground rod doesn't need to be connected to the house rod. and panel in garage is a subpanel, as it will be fed from a fused disconnect
poppasmurf
Original Author
16 years ago
Just bought 3/3 cable, so will go with 4 wire option. I do want to run a 2 way light switch into the house to run o/s lights @ garage when expected or unexpected guests arrive. My big problem is I don't have good access to house panel as the existing conduit is full. I'll get creative & find a way to the neutral, but for the ground- I'll connect to factory ground lug @ steel frame. It is a drop of 4' from house box. I'll bring the Hilti hammer drill home to drive the ground rods at the garage. Thanks for help-all of you. I'll try to return help at plumbing & gas fitting board.
blackadder34
16 years ago
poppasmurf- wouldn't you have access to neutral at 200A disconnect?

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