Adding Service for New Garage

[redfox]

I am building a 40' x 72' detached garage and am trying to figure out whether I can run 200A service to it (for welder, air compressor, plasma cutter, lights, heater, etc).

My current electrical setup is as follows:

* Power lines run underground from the poles to a transformer located about 100' from my house. (I have my "own" transformer ... no neighbors to share with.)
* Meter is located next to the transformer, mounted to a wood panel. Meter housing is rated for 375A. Power company will replace current 200A meter with whatever we need at no charge (yea!)
* Raceway above meter, goes to 200A main then underground to another 200A main mounted to the side of my house.

I want to add a second 200A main to the wood panel (next to the meter) and run power underground to the garage.

Questions:

1. Good idea? Bad idea? Why?

2. Can I have two separate 200A services based on the 375A meter housing? (I'd be willing to bet I'll never pull 400A at any one time)

3. Do I need another 200A main at the garage, similar to the setup at the house?

Thanks in advance!

[giddonah]

200A for a garage is a LOT of power. How many guys do you plan on having in there working at once? My friend runs all that off of a 60A sub without problems. If you can do it, then hell, go for it. You never know when you might have the crew from Monster Garage in there rippin' it up!

[montytx]

If you ever do pull 400 youll have to tell us how you did it...I agree with giddinah, 60 Amps should do it. But if you've got the time and money and a compulsion to do over kill then why not.

[Sparks]

Is the garage closer to the main meter or the house? I would feed from whatever is closer to save labor and material. Do you really need 200 amps, seems like a waste of money unless you did a load calc. and actually need this much which I doubt. I wouldn't install a separate service per se for the garage, just run a feeder from one of your existing load centers. You will need a sub-panel for sure in garage or outside of garage, wherever you prefer. You legally could install a 200 amp feeder breaker in an existing 200amp panel if you wanted to but the inspector may ask to see a load calculation performed. The garage will need it's own disconnecting means at the garage itself, your sub-panel can accomplish this. 4 wire feeder required and the garage will need a grounding electrode system. I think it would be senseless to install another 200 amp main at the meter when this task could be accomplished with a feeder supplied by an existing load center.

[redfox]

Thanks for the input, everyone.

Sparks --

The garage is about 50 feet east of the meter and the house is about 100 feet west of the meter, which is why I want to run the electrical from the meter to the garage.

I can forsee a situation where I would NEED 125A-worth of circuits at one time in the garage (a couple of guys working w/ BIG tools plus lights, heater, etc). If the cost of running 200A service is similar to that of running 125A ... why not?

I'm an electrical engineer (not an electrician) so I understand electric theory but am clueless about building codes. Does the NEC define a method for load calculations? (a section reference would be helpful)

Thanks again

[Sparks]

Article 220 gets into load calculations and demand factors but generally this would be useful more so when de-rating is needed. ie. apartment buildings wouldn't need a 6oo amp service even though they may have 10 units. Load calcs and demand factors applied here save unnecessary material.Your inspector may or may not want to see a load calc, I sort of doubt it, but some might. Back to your issue, you mentioned a main at the meter, a main could be a disconnect only or a load center, both are called mains. Which do you have at the meter? If it's a load center, then I would install a feeder breaker there to save time and money and run underground to the building, then to a sub-panel for the building. If you only have a disconnect, that a lot different. Now after you accurately figure your anticipated load for the house and garage and you're well over 200 amps, then that's a different story altogether. What does your power company recommend you do? They have planners/ engineers that are very helpful with advising on these issues. I would also make a call to your inspector or AHJ and ask him what he will allow and how he would like to see it done. Local requirements sometimes are more strict than the NEC. Also, different areas of the country do things differently in regard to services and the like. You are going to have to make some calls and find these things out.