Supplying Power to a Garage and Code Violations
June 20, 2007
Hello. I am trying to run power from my detached garage to my home. The garage is already wired inside, and it just needs to be powered up. Several questions here. Can I use THHN wire the whole way as long as I run it in conduit? I mean buried in the ground in conduit to the house and then run along the attic rafters (without conduit) to the breaker box. The county inspector says its okay, but some local electricians tell me I have to run direct burial and then connect to SE once I am in the house. I would prefer one long wire instead of connecting two together. If I can use THHN, and I want a 50 amp circuit, do I need #8 or #6 copper wire? If I have a grounding rod at both the detached garage and the house, can I get away with running 3 wires and not 4 and what size conduit would I need? Thanx very much.
A: Yes you may use THHN wire the whole way as long as it is in conduit all the way from the breaker box or a junction box in the garage to the breaker box or a junction box in the house. However, you may not run the THHN wire through the attic rafters, or anywhere else without conduit; the county inspector must have misunderstood your question.
I have the same recomendation as your local electricians. Copper prices are still high so, the THHN will cost considerably more than aluminum URD (direct burial) and changing over to aluminum SE cable at the house. This is how I would do it unless the ground is real rocky; then I would definately install conduit.
If you are going to use THHN copper wire installed in conduit, then #8 is rated for 50 amps maximum. However, if you are going to use aluminum URD (direct burial), USE (direct burial), SE or copper NM cable, then you need to use #6; which is rated for 50 amps maximum.
Use 3/4″ PVC minimum for #8 conductors or 1″ PVC minimum for #6 conductors. However, I recommend installing 1 1/4″ PVC minimum. This would allow you to increase the wire size to #2′s for 100 amps in the future. Fifty amps will work fine unless you are going to be welding and have a compressor running at the same time, then I recommend 100 amps.
If there is a gas line, phone cable, TV cable or data cable between the house and the garage, you need to install 2-hots, 1-neutral and 1-ground. If not, then you may install 2-hots and 1-neutral only. Then you need to establish a ground at the garage.
I have a breaker box come from the meter with two 40 amps breaker in it one for my air condition i want to tap into one side of the 40 amps breaker a run a # 12 wire to a room i’m add to my house is this a safe way to do this?
A: No this is very unsafe! Do not do this, you will cause a fire or electrocute someone. This is also a National Electrical Code (NEC) violation. You need to upgrade your breaker box from a 4-circuit to 6-circuit or larger. This will allow you to install a 20 amp circuit breaker maximum for your #12 wire.
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