OT - need electricians advice. detached garage

[JeramyK]

Hi guys,

We purchased a house back in April that has a detached 2 car garage. My problem is that the previous owner did not have electric service installed to this garage. Things have finally settled down enough to where I can finally start work on this project. I've done basic wiring before but this will be the first time on a project this big. I weighed the option of hiring someone to do the work but I'm confident I can do it right myself with a little help.

So far I've picked up a 125A sub panel to put in the garage. Now I'm at the point where I need to determine what type of wire I need to buy. Based on my calculations I'll need approx. 100ft of wiring. Approximately 30ft of this will be run underground from the back of my house to the garage. I figure I'll need to install a ground rod outside the garage as well?

In this garage I'll mainly be using a 7hp 60gal air compressor which needs a 240v line and draws approx. 40A when it kicks on. Also a Millermatic 210 mig welder which I believe needs a 50A circuit. Other than that I'd like to have enough left over to run some shop lighting, 3 or 4 regular electrical outlets and a garage door opener.

Any advice would be greatly appreciated. And if any other info is needed please ask.

[BenR]

I'm not an electrician, but I did bring power to my detached studio. I did a lot of the work and left the truly dangerous (to those who lack the tools and experience) stuff to a licensed pro. The project involved increasing the house's incoming power to 300 amps, putting in a new meter base to accommodate the power increase, running 250 mcm copper (if I recall correctly) from the new weatherhead, running a bundle of 4/0 underground in conduit more than 100 feet to the studio, and putting in a 200-amp panel in the studio.

I rented a Ditch Witch 1020 and did the trenching, I pulled the 4/0 bundle by hand the whole way (fun!), and I did all the wiring inside the studio and used GFCI for all outlet drops. The electrician put in the new weatherhead, ran the copper to the meter base, installed a new ground at the house, did final hookups in the studio's panel, and ran a ground there. I passed my inspection with flying colors. At the same time, I trenched a separate line on the other side of the studio for natural gas. I laid in 1" CTS and did all the plumbing myself. Passed all inspections with no problem. Had the gas service upgraded to 2 psi @ 500,000 BTU.

[tonyclifton]

You will need a ground rod at the garage.

Calculate the maximum simultaneous current draw for when that compressor and MIG are going, along with lights and the garage door opener kicking in, the TV and the refrigerator and someone else pulling a few amps on a power tool. Then you will know what size wires you need. I'd multiple it by 30% - run big pipes.

Are you going to put an electric heater in it?

[JeramyK]

I'm not planning to have any heating right away. Maybe down the road someday. It is a simple wood framed garage and right now it has no insulation. Even if I do insulate it I'd probably look into another form of heating instead of using electric.

I guess I should also mention that this garage is more for a hobbyist. By no means do I plan to run a business there. Maybe a few hours here and there in the evenings or on weekends. I have a 79 Camaro that I'm working on which is my main project. But I also like to do smaller welding projects occasionally as well. Very very rarely do I ever have the need to have the welder running with the air compressor, etc. all at the same time. In fact I might run the compresor or welder for an hour or two and then they might not get used again for a few weeks. It all depends on what I'm working on.

[Sberry]

I like number 2 alum for these, they sell a quad just for this at the box stores. Its a 100A wire, you can use up to 100 in your main panel to feed this. there is a good site that tells all you need to do this install.
http://www.selfhelpandmore.com/homew...sory/index.htm
Ignore the start up ratings on the comp, it will run from a 10 wire 30A breaker, the 210 requires a 30A circuit also. The FLA rating on the comp tells the actual story,, whats that number from the motor tag??? Number 2 fits in a 60A breaker and up to 70 they are cheap, 100 is a bit more pricey. Even a 60 will run this garage with only 1 or 2 guys working in it. This is a very common install and worth every penny.

[Sberry]

This wire will run down a 1 1/2 which is marginal with any turns, 2 inch is better. The wire is direct burial but must be piped anywhere its exposed. I really like the alum wire for these, its cheap and works well as the actual load is way less than a hundred, you can run 200 ft with 2% voltage drop @ 50A

[MysteryMan]

I'm not planning to have any heating right away. Maybe down the road someday. It is a simple wood framed garage and right now it has no insulation. Even if I do insulate it I'd probably look into another form of heating instead of using electric.

I guess I should also mention that this garage is more for a hobbyist. By no means do I plan to run a business there. Maybe a few hours here and there in the evenings or on weekends. I have a 79 Camaro that I'm working on which is my main project. But I also like to do smaller welding projects occasionally as well. Very very rarely do I ever have the need to have the welder running with the air compressor, etc. all at the same time. In fact I might run the compresor or welder for an hour or two and then they might not get used again for a few weeks. It all depends on what I'm working on.

one thing to think about for heating

if you are not going for electric and will not be in the shop every day all day then you might want to go with one of those forced air propane heaters
those round ones that puts out 40,000btu (the small ones at least) http://www.northerntool.com/webapp/w...&cm_ite=heater

I'd get one of the bigger types though as a shed such as the one you discribed will get really cold in the winter

just a thought

[JeramyK]

Thanks guys, I greatly appreciate the responses.

Sberry27, I don't know the FLA rating on the compressor off the top of my head but I do recall that at my old residence I paid an electrician to install the line for it. He had it originally setup on a 30A breaker but when I'd flip the switch to turn on the compressor it would trip the breaker. He put a volt meter on it and found it was drawing 39A when it kicked on. He put a 40A breaker on it and I never had another problem.

Should I need to change the main breaker inside the house at all? I believe it's a 150A currently.

[TOMWELDS]

I wanted to ask, how new is the service in the house?

[AfterhoursFab]

I just did this in my garage not too long ago with about the same run. Rent the ditchwitch and bury some pcv, 1-1/2" is enough but I went with 2" for easier pulling since mine was all underground. You will want to pull 3/0 for your mains, 4/0 for your neutral and 6/0 for your ground. Electrical code states that you MUST run seperate neutrals and grounds at any subpanel, so make sure you have isolated your neutral bar. Also you need to ground it back at the main panel, not to a grounding rod. Buy a bottle of wire lube and squirt it in the pipe, youre gonna need it.

[Sberry]

As Tom said how is the incoming? What are you running on it now such as electric appliances? I forgot to look where you were. Air cond is a factor, water heater, cooking, cloths dryer. Its not really about how big these numbers are but what load you apply to it. As for the comp it may have been an old style breaker. I would guess that comp to draw about 15 run or so. Modern breakers are now all motor load rated for lack of a better term and will handle surges for start ups. 39 start should not blow a 30, in fact that reading isnt really right for some reason, I would suspect it pulls closer to 100 than 40 on start. If you are not running the house wide open the 150 will handle things fine, if you wanted to at some future date you can always upgrade, wont have anything to do with the garage really unless you move the panel location.

[AfterhoursFab]

I just talked to my buddy who helped me do mine, supposedly if you run a ground rod out at the subpanel, you can run a smaller ground wire between panels, but the sub definetly has to be bonded to the main panel.

[Sberry]

You must run a ground rod, but it doesnt change the size of the wire. What does chage things is the size of the feed coductors. number 6 wire and a 60A breaker calls for number 10. Even if you use heavier wire and limit it to 60 you should upsize the ground to match the conductor ampacity. 8 for 100A and 6 for 200. This is one thing I like about the quadraplex, the wires are all sized. There are cases where you can use 3 wire feeds but I wouldnt, there are so many utilities anymore, phones, gas lines, water lines, even though it may be in compliance when its installed when someone comes and adds a phone line they unknowingly throw it out,,, so,, 4 conductors for all these subfeeds.

[TOMWELDS]

If it's an old compressor or doesnt have a genie unloader, i can see why it pops the breaker. I found this problem with my friends comp.

[JeramyK]

Sorry for not responding sooner to some of the questions. I was out of town for a few days.

I live in Pittsburgh, PA. The house was built in the late 50's but I'm not sure about the history of the incoming line. When we bought the house back in April we were told the service was "upgraded" but honestly I don't know exactly what they meant by it. I took a picture that shows what my circuit panel looks like. Not sure if it helps. I apologize for the massive picture size. Wanted to catch as much detail as possible.

http://users.adelphia.net/~jeramyk/circuitpanel.JPG

I do have a central air conditioning unit running on it's own circuit. I also have an electric dryer, microwave, and 2 refridgerators. Other than everything else is standard electronics. Lights, TV, computers, etc.

I priced the outdoor AL wire 2/2/2/4 at Home Depot and it was about $1.28 per foot. Does that seem about right? Do I need to run conduit the whole length underground or only on the 2 places where the cable is exposed leading to the house/garage?

Sorry for asking so many questions. Just trying to save myself some money if I can but at some point I guess I should consider hiring a pro.