what size wire from house to shop?

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Old 11-26-07, 11:42 AM
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what size wire from house to shop?

I am in the process of gathering materials for wriing my shop. Its a 30x50x12 and its close to 200' from the house. I have purchased a 125 amp breaker panel for it and have set 20 some odd 20 amp outlets around the shop. I'll have 10 2 bulb (4') fluorescent fixtures and 2 2 bulb (8') flourescents for lighting. I bought a big roll of 12-2 for all the outlets and lighting.

I'll have a grinder, a table saw, an air compressor, a 2 post lift and typical other shop tools but I dont expect too many of them to be on at the same time. I will eventually get some sort of heaters in ther and if its not a woodburning stove, it will probably be electric (maybe a heat pump or strips). I also have a lincoln 225 welder and plan on getting a mig somewhere down the road.

Not having a clue as to power requirements for those items listed above, I cant really tell how much power I'll need and more importantly, since I am ready to buy wire to connect the shop to the house 200' away, I dont know what size wire to buy.

what size wire do I need? I see some online calculators that say 3/0 is the min and I see other posts that say I could get away with 2/0 or even 1/0. I dont want to undersize it at all or oversize it too much

Can anyone with experience help me out?
 
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Old 11-26-07, 11:50 AM
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What size panel at the house? 200a? You need to do a load calculation on the main panel before adding the subpanel.
 
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Old 11-26-07, 12:31 PM
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theres a 100 amp panel at the house BUT I was told I could run a separate sub panel off the meter to run 100 amp out to the shop.
 
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Old 11-26-07, 12:49 PM
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Did I read that right, a 1,500 square foot shop? My whole house is only a bit over 1,500 square feet.

I am assuming that this is in an area that is zoned for residential and that you have no intention of using the shop space for any commercial purposes, right?

If it is only going to be you and maybe an occasional friend working in this shop at any one time then your electrical requirements will probably not be excessive. You have to allow for your lighting, air compressor (since it will be automatically starting) and the largest power tools / welder in use at one time. This would be your continuous (not in code terms) draw and then you add to this the starting draw of the largest motor. This calculation gives you the highest expected load and it is from this that you calculate the voltage drop over the 200 foot distance and calculate the necessary size of wire.

If this calculation gives you a lower sized wire than does the calculation for a 100 ampere feeder from the house then you use the proper size wire for the supplying circuit breaker (100 amperes) to the shop. If the voltage drop calculation shows a larger size wire is necessary to maintain the voltage drop to an acceptable level then you use the larger wire.

I would strongly urge you to NOT consider the use of electric heat in this shop because it will vastly increase your electrical needs. In all probability it would require no less than a 200 ampere feeder to the garage with allowance made for voltage drop AND a subsequent upsizing of the service at the house.
 
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Old 11-26-07, 01:09 PM
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yes, this shop is just for me to putz around in (no commercial stuff going on).

I have an old muscle car that i will be playing with and needed some room to put it and my truck. Since I had the land and the labor to build it, I went as big as I could afford (its taking a while to finish).

Anyways, i am undecided between running wire from my house out to the shop or just having another meter placed out there with an overhead service line. The meter and overhead line would just cost me the monthly service fee ($15 a month if I use no electricity and the service fee goes down from there- but the electricity is added to it). with the price of the wire, $930 for 500' of 1/0, I could put a meter in and cross over in about 7 years.

One of my biggest factoirs is that I dont want line drop and I really dont want to dig a 200' 24" deep trench in my rocky soil (it is on top of a hill so its pretty rocky). If I needed 2/0 or 3/0, the price of the cable goes goes up (not sure how much as I havent found a price for it yet) and the overhead line starts looking better- plus, with the overhead line I do not have to worry about maintenance or repairs if the underground gets damaged
 
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Old 11-26-07, 01:46 PM
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I would really lean toward having a second meter installed to the shop. First, I don't think that you have enough capacity with you existing 100A service to add this shop in addition to your house. This would require a service upgrade at the house which would probably be around $1,500. Second, the cost of the wire for a 200' underground will be pretty substantial compared to the meter fee from the power company.
 
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Old 11-27-07, 06:59 AM
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The power company says i have 200 amp service to the house. Thats 200 amps to the meter base. off the meter, there is a 100 amp breaker panel that feeds the house.

I was told I could run a separate panel coming off the the meter base (separate from the house panel) to run thru 100 amp breakers out to the shop. In the shop, I'll have the 125 amp breaker panel that has a 50 amp, a 30 amp and 6 20 amp breakers in it (no main breaker).

using various online calculators, it looks like I would need #1 or 1/0 THHN wire (and a #6 ground) from the house to the shop
 
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Old 11-27-07, 09:50 AM
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Originally Posted by aarcuda View Post
The power company says i have 200 amp service to the house. Thats 200 amps to the meter base. off the meter, there is a 100 amp breaker panel that feeds the house.
That makes the situation a little better then. Are there or will there be any other metallic pathways between the house and the shop? Phone lines? Cable TV? Water pipes?

I was told I could run a separate panel coming off the the meter base (separate from the house panel) to run thru 100 amp breakers out to the shop.
Does your meter also have a 200A main panel attached in a meter/main combo? Do you know if your meter base is double lugged?

In the shop, I'll have the 125 amp breaker panel that has a 50 amp, a 30 amp and 6 20 amp breakers in it (no main breaker).
A main breaker will be required for this panel.

it looks like I would need #1 or 1/0 THHN wire (and a #6 ground) from the house to the shop
The minimum size wire you can use is #4-4-4-8 copper or #2-2-2-6 aluminum based on table 310.15(b)(6). Either of these provides about 5% voltage drop at maximum load. Code does not require you to upsize wires for voltage drop, but you might want to get to 3% which is the standard design goal. Using #2-2-2-6 copper or #1/0-1/0-1/0-4 aluminum achieves that goal. You could also use #1-1-1-4 aluminum to save a little cash which yields 3.6% voltage drop at max load -- certainly close enough to acceptable limits.

If you use THHN, you'll also need conduit. A direct burial aluminum cable such as USE (underground service) or MHF (mobile home feeder) may be a good option for you also. It's usually quite a bit cheaper than conduit and THHN.
 
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Old 11-27-07, 11:47 AM
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Originally Posted by ibpooks View Post
That makes the situation a little better then. Are there or will there be any other metallic pathways between the house and the shop? Phone lines? Cable TV? Water pipes?
Yes, I was going to run a water line (1" pvc) out to the shop in the same trench. I was told it needed to be a foot away from the wires (is that right?)

Does your meter also have a 200A main panel attached in a meter/main combo? Do you know if your meter base is double lugged?
the meter has a panel attached to it but that panel has a 100Amp breaker in it with all the house's breakers. As for the meter base being double lugged, I am not sure. I hope so or else I believe I'll need to change that out to a double lugged base (is that right or is there a way to make a single lug base into a double lug base?)


A main breaker will be required for this panel.
I didnt know this. I thought the main breaker could be at the house only. If it was in the panel at the shop AND at the house, I suppose there wouldnt be a problem- Id just need to buy the right panel. Is that a code thing?


The minimum size wire you can use is #4-4-4-8 copper or #2-2-2-6 aluminum based on table 310.15(b)(6). Either of these provides about 5% voltage drop at maximum load. Code does not require you to upsize wires for voltage drop, but you might want to get to 3% which is the standard design goal. Using #2-2-2-6 copper or #1/0-1/0-1/0-4 aluminum achieves that goal. You could also use #1-1-1-4 aluminum to save a little cash which yields 3.6% voltage drop at max load -- certainly close enough to acceptable limits.
Wow, thats a lot smaller than I thought (and smaller than the calculators say I need. How do you come up with those gauges?

If you use THHN, you'll also need conduit. A direct burial aluminum cable such as USE (underground service) or MHF (mobile home feeder) may be a good option for you also. It's usually quite a bit cheaper than conduit and THHN.
I initially believed I needed the 1/0 wire and I couldnt find any undergroung service type wire in that size. I'll ask my electrical supply house
 
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Old 11-27-07, 01:00 PM
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Originally Posted by aarcuda View Post
Yes, I was going to run a water line (1" pvc) out to the shop in the same trench. I was told it needed to be a foot away from the wires (is that right?)
About a foot away is fine. The reason I asked is that if you have metal paths other than the wires, then a fourth ground wire is required. If there are no other metal paths, then you only need to install hot-hot-neutral. Since you have the water line, I would install the ground wire.

You may also want to consider installing a second conduit for low voltage wires if you ever want telephone, computer, cable TV or security system out at the shop. If you dig a 24" trench, put power at the bottom, backfill 12", then install the low voltage conduit and fill to grade. One trench, two conduits with 1 foot separation.

the meter has a panel attached to it but that panel has a 100Amp breaker in it with all the house's breakers. As for the meter base being double lugged, I am not sure.
It sounds like you have a 100A meter/main combo which I would give 90% chance of needing to replace that with a 200A meter/main box to complete this project. I don't believe that meter/main units are typically double lugged. You could have a power company technician out to pull the meter and take a look in there.

I didnt know this. I thought the main breaker could be at the house only.
A main breaker is required for any detached structure which has more than six total breakers/circuits. If you come directly off the meter, you need a main breaker for overcurrent protection anyway.


How do you come up with those gauges?
There are two NEC tables 310.15(b)(6) and 310.16 which specify the required gauges for residential services and various other conductors respectively. Then I used an online voltage drop calculator to upsize for distance. Once you consider the upsize, both table 310.15(b)(6) and table 310.16 are satisfied so you should be okay.

You've gotta be careful using online calculators. They often only size for just voltage drop or just NEC tables, but not both. You need to consider both requirements in determining the final gauge.

I initially believed I needed the 1/0 wire and I couldnt find any undergroung service type wire in that size.
It's possible the supply house doesn't regularly stock 1/0; it's not a terribly common size. They can probably order it though. Common sizes for installations in which distance is not a factor are #2 for 100A, #2/0 for 150A and #4/0 for 200A so it wouldn't surprise me if they don't regularly stock #1/0 aluminum.
 
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Old 11-27-07, 01:56 PM
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so seeing as this is going out 200' from the house meter, using #1 wouldnt be too small but, would actually be a size or 2 bigger than code, right?

Does #1 come in a 3 or 4 wire cable (an all in one)? I'd like to be able to talk somewhat intelligently to the guy at the electrical supply store.

Also, I betcha that I will have to change out my meter base to get the double lugs. Would there be a model number or anything like that on the one on my house where I can look up what it has? or is the only way to tell to have Entergy come out and pull the meter and actually look at it?
 
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Old 11-27-07, 02:22 PM
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Originally Posted by aarcuda View Post
so seeing as this is going out 200' from the house meter, using #1 wouldnt be too small but, would actually be a size or 2 bigger than code, right?
Correct. #1 aluminum would be okay for a 100A subpanel at 200' distance.

Does #1 come in a 3 or 4 wire cable (an all in one)?
I'm sure some manufacturer somewhere makes just about every configuration -- you'd want the four wire. If you ask for it they can probably order it from one of their manufacturers if they don't have it in stock. I just checked CerroWire catalog and they don't make a #1 al USE or MHF, but another wire manufacturer probably does.

Also, I betcha that I will have to change out my meter base to get the double lugs.
I think so.

Would there be a model number or anything like that on the one on my house where I can look up what it has? or is the only way to tell to have Entergy come out and pull the meter and actually look at it?
I think a visual confirmation would be the best.
 
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Old 11-27-07, 04:14 PM
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Two small things:
You can get double lugs but you will have to get them from a supply house.

If you run you wire in Sch 80 PVC you only have to burry it 18"
 
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Old 11-28-07, 06:32 AM
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thanks for the replies.

I was totally in the dark when I began this hunt for information and you guys really helped out a lot.

I was confused about the neutral wire too as I kept thinking it was the same as the ground (and therefore I was initially going to get #6 for the neutral). But Im thinking thats not true and that the neutral should be the same size as the hots. Should the neutral be the same size as the hots (ie, #1 wire for the neutral as well?). I know the ground wire can be smaller and I was going to use #6 for the ground.

On a side note, i looeked at the breaker panel for the house and it is actually a 150 amp panel and not 100 amp as I initially stated.

The meter base has no markings on it at all but it looks like the original one installed when the house was built in 1985. I'll call the supply house today about the meter base.


thanks again. Im am learning a lot through all this!
 
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Old 11-28-07, 09:32 AM
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Originally Posted by aarcuda View Post
Should the neutral be the same size as the hots (ie, #1 wire for the neutral as well?).
Generally the neutral should be the same size as the hots. There are conditions where you can use a size or two smaller neutral, but typically you would only do that if you had a large percentage of the load dedicated to only 240V appliances and you could prove it with a load calculation.

I know the ground wire can be smaller and I was going to use #6 for the ground.
If you use #2 aluminum hots, you need a #6 aluminum ground. If you use larger than #2 hots, you need #4 aluminum ground.

the house and it is actually a 150 amp panel and not 100 amp as I initially stated.
That would be a problem for double lugging the meter. If your house is 150A and your shop is 100A, that puts 250A of load on your 200A service drop and meter.

You would need to upgrade the 150A panel at the house to a 200A panel, then install the shop panel as a 100A subpanel off the new 200A main.
 
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Old 11-28-07, 09:50 AM
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Originally Posted by ibpooks View Post
That would be a problem for double lugging the meter. If your house is 150A and your shop is 100A, that puts 250A of load on your 200A service drop and meter.

You would need to upgrade the 150A panel at the house to a 200A panel, then install the shop panel as a 100A subpanel off the new 200A main.
CRUD! Well that changes everything- maybe. I dont want to change out the house panel as well.

but you got me thinking. There is a 220v line that is already coming out of that box that is disconnected now. I kind of came to the conclusion that it had been used previously for a well pump. It may be only a 30 amp breaker though.

well shoot, its looking better to just run a separate service at the shop and pay the extra $18 a month.
 
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Old 11-28-07, 09:58 AM
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You can install the shop panel as a sub off your current 150A panel, but based on the loads you've described for the shop I really think this will overload your current service. You could do a detailed demand load calculation of the house and shop to determine if the existing 150A service is adequate to support both. Google for "demand load calculation" or get a decent home wiring book from the hardware store to get the details on this calc.
 
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Old 11-28-07, 12:41 PM
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well, the "service" to the house is 200Amp and the meter is a 200 amp meter. it is only the breaker panel that feed the house that is 150 amp (the main breaker in the panel is 150 amp).

If I replace just the meter base to get a meter base with double lugs (so I can hook up both panels to the meter base without doubling up on a single set of lugs), I suppose it is theoretically possible to load up 100 amps at the shop and 150 amps at the house but I dont think that is likely. I just dont have anything really huge to load me up that much.

Is there a code requirement that prevents me from having a 150 amp panel for the house and a separate 100 amp panel to the shop bith of which is fed from the 200 amp meter (if there are double lugs on the meter?).

even if I ran my Lincoln stick welder for 30minutes to an hour (which I believe will be my BIGGEST load and only used MAYBE once a year- ive never used it yet btw), that only draws 50 amps. and add to it a couple of lights, i wont be drawing 100 amps at my shop at one time- ever.

the compressor is probably only 15 or 20 amps max and the lift is rated at 17-18 amps and theres no way I'll be lifting and welding at the same time.

I guess I could add up the washer, dryer, hot water heater, stove, over, and dishwasher and AC (or heater to see what they would max me out at)
 
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Old 11-28-07, 01:54 PM
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Originally Posted by aarcuda View Post
well, the "service" to the house is 200Amp and the meter is a 200 amp meter. it is only the breaker panel that feed the house that is 150 amp (the main breaker in the panel is 150 amp).
It's a mincing of terms, but what you have is a service drop (wires from the power company) which is capable of 200A and a 150A service (main panel) as it sits. To upgrade to a 200A service which would utilize the full potential of your service drop, you may need to replace the meter box, main panel, and upgrade the grounding and bonding to correspond with the larger service.

I suppose it is theoretically possible to load up 100 amps at the shop and 150 amps at the house but I dont think that is likely.
It's not likely, but it's possible which makes it a violation of code and probably of the power company service standards also.

Is there a code requirement that prevents me from having a 150 amp panel for the house and a separate 100 amp panel to the shop bith of which is fed from the 200 amp meter (if there are double lugs on the meter?).
Yes, the NEC would prevent that and the power company standards would probably prevent that. You would risk heat damage or a fire at the meter base and service drop. Remember the breakers are there to protect against the worst case, not the typical case.

even if I ran my Lincoln stick welder for 30minutes to an hour (which I believe will be my BIGGEST load and only used MAYBE once a year- ive never used it yet btw), that only draws 50 amps. and add to it a couple of lights, i wont be drawing 100 amps at my shop at one time- ever.
This is why you should do a full load calculation of both the house and the shop to determine if your existing 150A service is already capable of supporting both as-is. If you have gas appliances, small air conditioner and no spa or other huge loads your existing service may be okay to simply install the shop as a subpanel.
 
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Old 11-28-07, 02:55 PM
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The info you have provided is excellent! I thank you again.

I have called the power company and asked them what would I need to do to the service line IF I wanted to (or had to) go up to the next size service (i.e., 320 amp). They said that all I'd need to do is make an appointment with them to come out and shut off the power while I change out the meter base to a 320 amp meter base (and of course, this would be a double lug meter base to set me up for the shop hookup).

I asked them if the line that runs from the pole to my meter box would require upgrading and she said that it wouldnt. She also said I could have one of their engineers come out and do this load calculation to see if I need the larger service for what I need to do.

So it looks like I might have it close to being wrapped up. After I talk with this power guy, I'll let you know what he says and then its GO time! thanks!!
 
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Old 11-28-07, 03:04 PM
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I am going to make several assumption and explain some possible options.

Assuming that you presently have a 200 ampere service drop and a 200 ampere meter with 150 ampere service conductors to a 150 ampere main breaker in a 150 ampere panel.

You could install a 200 ampere panel at the meter with a 150 ampere breaker to feed the existing service panel which would then become a sub-panel. A 100 ampere breaker would then be installed in this new (Service) panel to supply the shop.

OR

You MAY (with local utility and AHJ approval) be able to install a 200 ampere fused switch (or single circuit breaker enclosure) next to the meter, with 150 ampere fuses (or circuit breaker, as appropriate), to supply the present service panel, which would then become a sub-panel and install a second 100 ampere fused switch (or single circuit breaker enclosure) to supply the shop. This second option assumes the existing meter has the double taps.

All of these options require the present service panel to become a sub-panel with all of the requirements of isolated neutral and bonded equipment grounding.
 
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