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You are here: Experts > Home/Garden > Home Improvement/Repair > Electrical Wiring in the Home > Shop Wiring
Expert: Greg Hughes - 11/6/2009
Question
QUESTION: I recently built a shop and need to get power to it. An electrician suggesting taping my main power into the house and going through my attic rather than ditching. He suggested 1/0 aluminum. The run will be about 300 feet. Shop is general duty homeowner. Maybe 1 220v for welder rest will by homeowner grade woodworking tools. What do you think?
ANSWER: The attic is better than a ditch. I do not like aluminum so I always suggest copper. The size of the wire will depend on how many amps you want/need.
It sounds like 60 amps would be plenty for you.
At 300 feet your copper size for 60 amps would be #0 or #2 depending on the actual length.
You will want a subpanel.
For every one hundred feet you have to go up a size. For 0-100' you would use the normally rated size. For 100-200' you would go up one size, etc.
The reason is for voltage drop. Just like in plumbing if you have a long run you have to go up a size to get the proper volume and pressure.
---------- FOLLOW-UP ----------
QUESTION: Thank you for the prompt and thorough answer. I will use your suggestion and go through the attic. What size wire should I use in the building itself, 12/2 or 10/2? The cost per foot will be about the same. I am planning on putting no more than 2 outlets on a circuit. Is there a formula to determine how many lights to use in the shop itself, the shop is 30x40x15 feet. Is EMT rigid conduit better to use or the schedule 40 pvc? Any other suggestions you might have to prevent re-wiring in the future would be appreciated.
Answer
The amount of lighting will depend on several factors. One is your age, another is what type of equipment you will be using, and the other is how much natural lighting there will be.
If you will be using machinery that spins you will want to install florescent lights with an electronic ballast. Do not use the magnetic ballast!
You will want florescent lights up high for ambient lighting, then you will want lights for task lighting. I recommend track lights for the task lights so they can be directed and moved to give you the best lighting on the job you are doing.
Put the lighting on different switches so you do not have to them all on at the same time. The only formula you need will be for the wattage. A 20 amp circuit at 110 volts can take about 1750 watts.
10/2 is better than 12/2 but if you divide up your circuits well it would be a little overkill, and 12 gauge is easier to work with.
For a shop I like rigid. Run stranded wire and it will make the pulls easier.
The trick to stranded wire on screws is to leave a small piece of the sheath on the end to keep the wires together.
Remember to keep the neutral and ground unbonded at the subpanel.
Check the specs for your welder and any equipment like that so you run the right size wire and circuit breaker.
Think about fans, heaters, and cooling now so you can run the wiring.
The nice thing about a subpanel is you can add to it pretty easily, but now is the best time to run the wires.
Buy the thin breakers so you can fit enough in the panel.
If you think you might want another circuit sometime in the future run the conduit now. You can pull wires later but at least you do not have to move everything to put in conduit later.
If you have more than one entryway put some ambient lighting on a three-way switch.
Also, think about lighting outside. Security and entryway.
That is all I can think about now.
Hope that helps.
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