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Garage sub-panel

I want to upgrade the wiring in my detached garage. It was built in 1961 and has a 3-wire #6 cable (2 hots and a neutral, no ground wire) run from a 30 amp breaker in the main panel in the house to a small fuse box in the garage. From the fuse box there is a 220v outlet plus (2) 110v circuits with screw in fuses. The existing wiring is a mess, hacked by previous owner, chewed by rodents, no grounds so it all needs replacing.  I want to install a new sub panel, delete the 220v outlet and have (4) 110v circuits for lights and outlets. No large loads anticipated, just standard hand tools and such, separate circuit for a door opener, mostly LED lighting. It is close to 100 feet from the main service panel to the garage panel.

Current code requires a 4-wire system for new work but has an exception for existing systems. When I poke around on the interweb for 3-wire systems, I get a little confused on how to do this in terms of grounding. Once I have the sub-panel hooked up the circuit wiring is straightforward. Different people seem to have different ideas. Looks like I need a dedicated ground rod (or 2) for the garage and it would be connected to the same bus bar as the white neutral feed wire. The feed wire comes thru a non-metallic underground conduit and there are no other metallic paths bonding the 2 buildings. The feed line has a standard breaker, no GFCI. This is a rental and running a new 4-wire feed would be physically and fiscally painful.

Re: Garage sub-panel


With a disconnect in the garage, you will want to have its own ground rod, I would have two of them. One on each side of the building. If the code for that requires 3 plus a ground, then that is what you pull. Voltage drop will determine the size wire needed. I would go one size above the minimal size required. Remember, the NEC is only a starting point for minimum requirements. You may go above and beyond. You need to determine the voltage drop between structures. The ground wire(s) from each rod needs to be conencted to the grounding bus, not the neutral. Even though they are not required every where, I would still use AFCI\GFCI devices in the garage. I would also pull the wire thru conduit every where in the building, and especially feeding the building. Use at least 4 inch conduit. In the future, if you want a larger ampacity, pull out the old, pull in the new. Easy as that. Dig the ditch only once. Dig the ditch as deep as the backhoe can reach. NEC requires a minimum of 18 inches in conduit. I dug my service entrance ditch 8 feet deep, as far as the backhoe would reach down.

I installed a separate 200 amp service for my work shop and garage. I have a 4 car garage and 2000 square feet of work shop. This size covers everything I have currently and plenty for future machinary and tools.


Handy Andy In Mt Airy NC

Re: Garage sub-panel

You can dig a trench and run a bare copper wire from the sub panel to the house and connect to the ground in the house. In the sub panel the neutral buss and the ground buss are sperate. 2 gound rodes connected to the sub panel ground buss.#6 wire is more than sufficant for what you say you want installed.

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