Wiring garage from 100amp service to house

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Old 06-25-10, 08:50 AM
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Wiring garage from 100amp service to house

Hi,
I have a question about my detached garage that I am wiring. I have a 18x20 garage that was wired when I bought the house, there is just a 30 amp breaker from the house going to the garage then in the garage there is just a 15amp breaker running 3 outlets and a couple lights. Now I have added a 24x24 onto the back of the existing garage and have started wiring it but I am unsure of how to power it. I only have a 100amp service in the house; I heard it can be a bit spendy to upgrade to a 200amp service. So the question I had was, I have a friend that used to do electrical work and he was thinking it might be possible to run another power line right from the meter out to the garage then I would have a 100amp box in the house and a 100amp in the garage, is that possible?? If not and the best thing to do would be upgrade to a 200amp service what would all the costs be for that upgrade? My friend could help me put in a 200amp box in the house and run wire out to the garage, then would I need to pay the electric company to put in a new meter and run new wire to the house? Sorry for the long post, I just wanted to try to get all of my questions in at once. Thank you very much for any help. FYI I live in MN Anoka County.
 
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Old 06-25-10, 10:05 AM
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Originally Posted by Mr.T_1978 View Post
there is just a 30 amp breaker from the house going to the garage then in the garage there is just a 15amp breaker running 3 outlets and a couple lights.
What size and type of wire feeds the garage panel? Is there an underground conduit, if so what size? How far is it from the house panel to garage?

Now I have added a 24x24 onto the back of the existing garage and have started wiring it but I am unsure of how to power it.
Depends on what you plan to do in the space. Is this storage or a workshop? What kind of tools do you plan to use? Heat/AC?

I only have a 100amp service in the house; I heard it can be a bit spendy to upgrade to a 200amp service.
Usually in the neighborhood of $2,000 for an electrician to do it. You may or may not be able to do it yourself depending on local laws. The service upgrade may not be required unless you plan to add substantial load in the garage. Give us an idea of how much power is already used in the house -- square footage, gas or electric on the major appliances & heat, AC or spa installed? Is there space in the panel and is it reasonably modern (no fuses, decent brand)?

100amp box in the house and a 100amp in the garage, is that possible??
That's a type of 200A service, which would require pretty much everything upgraded too. If there's not too much load in either building you might be able to power the new garage from the existing 100A panel.

I need to pay the electric company to put in a new meter and run new wire to the house?
Depends on the power company. The homeowner is usually at least responsible for the main panel, meter box, and conduit or cable up to the mast on the house or down to the trench. Who pays for the material and labor out to the pole varies by location.

Sorry for the long post, I just wanted to try to get all of my questions in at once. Thank you very much for any help. FYI I live in MN Anoka County.
No problem at all, we're glad to help.
 
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Old 06-25-10, 11:45 AM
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Sorry, I guess I left out a lot of info.

Originally Posted by ibpooks View Post
What size and type of wire feeds the garage panel? Is there an underground conduit, if so what size? How far is it from the house panel to garage?
I don't recall what size it is right now, it has orange colored insulation. It is run underground through conduit, maybe 1 1/4". It is about 15-20 feet from the garage panel to the house. My plan is to just remove the existing garage panel (it only has 2 breakers in it) and wire that is currently running out to it and use a bigger box to wire the whole garage.

Depends on what you plan to do in the space. Is this storage or a workshop? What kind of tools do you plan to use? Heat/AC?
The front part of the garage I don't plan on doing anything different with the wiring, there is only enough room to park our 2 vehicles. But the back part of the garage is going to be used as more of a workshop that I will run a compressor (120v), mig welder (115v) and various hand power tools. It also appears I will have a gas heater to run, originally I wanted a wood stove but my home owners insurance didn't like the sound of that

Usually in the neighborhood of $2,000 for an electrician to do it. You may or may not be able to do it yourself depending on local laws. The service upgrade may not be required unless you plan to add substantial load in the garage. Give us an idea of how much power is already used in the house -- square footage, gas or electric on the major appliances & heat, AC or spa installed? Is there space in the panel and is it reasonably modern (no fuses, decent brand)?
The house is 2000 sqft, I've got AC/heat, washer, dryer (electric), fridge, stove (electric), dish washer, water heater (gas). I don't recall the brand of the panel, the house was build in 1970, there are probably 4-5 spaces open.

That's a type of 200A service, which would require pretty much everything upgraded too. If there's not too much load in either building you might be able to power the new garage from the existing 100A panel.
From listing out what the house is running I'm now guessing the best thing would be to upgrade the service.

Depends on the power company. The homeowner is usually at least responsible for the main panel, meter box, and conduit or cable up to the mast on the house or down to the trench. Who pays for the material and labor out to the pole varies by location.
I got some aluminum #4 (iirc) wire to run the power out to the garage is that big enough to handle 100amps?

Sorry if some of these questions are a bit newbish, my experience is only with wiring outlets and switches I haven't messed with the big power stuff.
 
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Old 06-25-10, 12:26 PM
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Originally Posted by Mr.T_1978 View Post
I got some aluminum #4 (iirc) wire to run the power out to the garage is that big enough to handle 100amps?
No, but it is big enough to handle 50A which I think will be plenty for what you want to do out there. Please review this diagram made by one of our members Bruto for what to do with the panel.



You can put in a 100A panel like 12 space or 16 space, very common item at the big box. You can re-use your 1-1/4" conduit -- use the old cable to pull in the new wires. The hot,hot,neutral wires should be #6 copper or #4 aluminum; the ground should be at least #10 cu or #8 al. The #4 wire you have may be acceptable if it it THWN or XHHW. Please post back if it's a different type.

The double-pole breaker in the main should be a 50A, the subpanel does not require a main breaker unless you have more than 6 circuits installed. All 120V receptacles in the garage/workshop must be GFCI protected.

From listing out what the house is running I'm now guessing the best thing would be to upgrade the service.
It doesn't sound like a service upgrade is absolutely necessary. There is a calculation called "demand load" you or an electrician can do to get an official figure but I think you are okay for a 100A service.

Sorry if some of these questions are a bit newbish, my experience is only with wiring outlets and switches I haven't messed with the big power stuff.
No problem. It's better to get it right.
 
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Old 06-25-10, 05:08 PM
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I would recommend going ahead with upgrading your service to 200 amps and then installing the subpanel in the garage as ibpooks has detailed.
 
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Old 06-26-10, 11:24 AM
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That sounds good, thanks for the great post!

Originally Posted by ibpooks View Post
No, but it is big enough to handle 50A which I think will be plenty for what you want to do out there. Please review this diagram made by one of our members Bruto for what to do with the panel.
I just went out to the garage and took a look at the wire I have, it's not 4 it's 2 awg, on the wire it says: "MT 2 awg al xlp 600v type use-2 (ul)" so since it is even bigger I assume I won't have any problems running 50 amps through it.

You can put in a 100A panel like 12 space or 16 space, very common item at the big box. You can re-use your 1-1/4" conduit -- use the old cable to pull in the new wires. The hot,hot,neutral wires should be #6 copper or #4 aluminum; the ground should be at least #10 cu or #8 al. The #4 wire you have may be acceptable if it it THWN or XHHW. Please post back if it's a different type.
I did end up getting a 100A panel that was on sale at one of the stores.

The double-pole breaker in the main should be a 50A, the subpanel does not require a main breaker unless you have more than 6 circuits installed. All 120V receptacles in the garage/workshop must be GFCI protected.
Yep this sounds good, I do have all the circuits GFCI protected.

It doesn't sound like a service upgrade is absolutely necessary. There is a calculation called "demand load" you or an electrician can do to get an official figure but I think you are okay for a 100A service.
I haven't had a chance to look into calculating this but I would be interested to figure this out later.


Once again thank you very much for your help and advice. I'm going to have my buddy come over in a couple weekends to help me finish this up.

CasualJoe - thanks for the advice as well, but I think I will try with running the 50amps first and if I run into issues down the road then I will look into upgrading.

-Todd
 
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Old 06-26-10, 03:29 PM
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CasualJoe - thanks for the advice as well, but I think I will try with running the 50amps first and if I run into issues down the road then I will look into upgrading.
My comment was just my recommendation based on your current load and square footage. Your plan may work just fine, but I believe you could find times when you are running on the edge of being overloaded.
 
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Old 06-28-10, 10:04 AM
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Your #2 USE aluminum is good up to 90A, although there is no problem limiting to 50A or 60A. Breakers above 60A are usually a lot more expensive so only get it if you need it. The hots can be black and the neutral may be wrapped with white tape. The ground should be green or bare.

The accompanying ground wire should be #6 aluminum or #8 copper. The ground wire must be sized to match the hots even if you aren't using them to full capacity.

You may need to buy a lug kit to attach the #2 neutral in your main panel. Most neutral bars can only take up to #4. You also might need to splice down to smaller wire to fit into the breaker lugs depending on the make of your panel. Some breakers can take up to #2 right to lug so that might be part of your decision when selecting breaker size. Your electrician friend also may be able to crimp studs onto the wires to better fit the breaker.
 
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