Service Wiring to my new Workshop help please.

[Marion Smith]

Ok, time for another wiring question.
My 100amp electric service run will be 170 feet from House Main to the Workshop Subpanel.
Wire will be run in conduit underground.
I am choosing Copper Wire.
What gage and type wire options do I have?
I "THINK" I have an open spot in my house main panel to use, how to tell for sure?
Can I come up out of the ground "under" my workshop and into a studspace?
My Workshop Subpanel I picked out has 24 spaces, good?
I'll also need some guidance on what I'll need to buy to make this a reality before its too cold.

[Jesse Busenitz]

Haha, I was just going through this on my shop except I'm doing 200 amp @ 100' using 4/0 aluminum.... I have a friend who's an electrician so I've been pestering him with all sorts of questions.
Subpanel all depends on what you all need to run. 220 requires two slots. You can do some shortcutting( not recommended) and get away with fewer breakers but definitely on your main machines you really need a dedicated breaker.

[Rollie Meyers]

Haha, I was just going through this on my shop except I'm doing 200 amp @ 100' using 4/0 aluminum.... I have a friend who's an electrician so I've been pestering him with all sorts of questions.
Subpanel all depends on what you all need to run. 220 requires two slots. You can do some shortcutting( not recommended) and get away with fewer breakers but definitely on your main machines you really need a dedicated breaker.

4/0 AL is not rated for 200A, see NEC table 310-16. Edit: The 2014 NEC changed that table to 310.15(B)(16).

[Wade Lippman]

I "THINK" I have an open spot in my house main panel to use, how to tell for sure?

If you don't know how to tell if you have room in your main panel, then perhaps this isn't a DIY job for you?
100a is an awful lot; if you actually need that much, are you sure your service has the capacity for it? My subpanel, with all the normal 3hp shop tools on it, needed 30a.

[eugene thomas]

That 4/0 poped at me as not rated for 200 amps but not a wire man by trade.... In the end though the your better to talk to a electricsn or if doing yourself the local building inspector.

[Jesse Busenitz]

http://www.lowes.com/pd_70202-295-55418406___?productId=3129327&pl=1&Ntt=4%2F0+wire I'm not a pro electrician, just going off of what my electrician told me, and what I'm seeing in the description on Lowes. I'm going to have some loss with that distance but not enough be concerned. Correct me if I'm wrong.....

[Rollie Meyers]

Table 310.15(B)(6) in the 2011 NEC edition & earlier allow smaller/ undersized conductors for dwelling services that carry the ENTIRE load, it does not apply to outbuildings, subpanels, or non-dwelling services, the only way to use 4/0 AL for a 200A service is to have load calculations that prove the load is under 180 amperes, then the next standard breaker/ fuse size rule can be applied since 4/0 AL in the 75 degree column is 180A, & the next standard size fuse or breaker is 200A, otherwise a 175A breaker has to be used. Table 310.15(B)(6) has been removed from the 2014 NEC & load calculations have to be done to be allowed to undersize the conductors for a dwelling.

Table 310.15(B)(6) has been one of the most misused items in the NEC, people use it for commercial services, subpanels, outbuildings where it does not fit the criteria of the code language.

[Marion Smith]

Okay, here is why I said "I think". At first glance, there are 4 empty spaces left on my Square D panel cover, for a total of 24 spaces...never been in it yet.
However, upon removing the cover, I see there is NO room left.
Is this common practice to put a 24 space cover on a 20 space load center?

[Allan Speers]

I "THINK" I have an open spot in my house main panel to use, how to tell for sure?


Marion, I know you're trying to learn, and that's great. However, if you don't even know the answer to that question, then this is probably a job you need to have an electrician do, start to finish. You don't want to make any mistakes with a 220v line.

[Rollie Meyers]

Okay, here is why I said "I think". At first glance, there are 4 empty spaces left on my Square D panel cover, for a total of 24 spaces...never been in it yet.
However, upon removing the cover, I see there is NO room left.
Is this common practice to put a 24 space cover on a 20 space load center?

Yes, too expensive for tooling to have two different panel fronts when they are so close in the number of spaces. Best advice is assume nothing.

[Brian Hood]

Hi,
I think you can do this project yourself, but a visit from an electrician wouldn't hurt. You're probably going to spend a fair amount of time figuring a few things out.

I'm going to tackling the questions in a different order, the order I would have approached them in (electrician and EC for 35 years).

1. First, determine the load, but don't just add everything up. Mostly what is the amperage of the largest motor x 1.25? Will there be heat? If you reply with a list of fixed loads I can help you.

2. Calculate or estimate the voltage drop- that's how you determine the size of your conductors. In most cases running tools (saws) at 220 vs 120 doesn't matter, you get the same performance, but in your case due to the 170' it will matter. You'll want to go 220 as much as you can, or increase the wire size.

3. Determine if you have space in your house panel. There are 'piggy-back' or tandem breakers for many panels that will allow you to double up some 120v loads and free up some space. Otherwise you can install a sub-panel right near your existing panel ($$). I advise against combining two circuits into a single breaker to free up a space unless you know exactly what you are doing, use a piggy-back if you can.

4. The size of the breaker at the main panel can be sized to the load (#1 above). You might end up with a 40 or 60 amp breaker connected to wire that can handle 100 amps, that's OK. I don't think you are going to pull 80 amps continuous to your shop. If you are you need much bigger wire, it's voltage drop that will make your motors wimpy and then eat them.

5. A 24 space panel for your shop may be too big, too small, or just right. Depends on what you are doing. How many outlets and what are you plugging into them (again, #1 above.)

6. Yes you can come up in a stud bay if you want, remember to keep the number of bends to two if you can otherwise pulling that wire will kick your butt. You will want a disconnect in that panel so get one with a main breaker, it will probably be 100 or 125 amp but it doesn't matter, it's just a big switch.

ps. for lighting, consider the Pixie Panel Flatlight from Home Depot. Very nice light and only 1/2" thin.

http://www.homedepot.com/p/Pixi-2-ft-x-2-ft-90-130-Volt-Edge-Lit-LED-Flat-Light-Luminaire-FLT22R27MD3644/203599918

pps. You will save money running aluminum instead of copper- you power utility certainly connected to your house with it and the electrons don't care. Just need to be slightly more thorough with the connections and after a month or so turn off the breaker and tighten them up once. The wiring in the shop should be copper.

Hope this helps, best of luck,

Brian(J)

[Rollie Meyers]

pps. You will save money running aluminum instead of copper- you power utility certainly connected to your house with it and the electrons don't care. Just need to be slightly more thorough with the connections and after a month or so turn off the breaker and tighten them up once. The wiring in the shop should be copper.

Hope this helps, best of luck,

Brian(J)

Improperly torqued conductors are a problem it does not matter if they are copper or aluminum, and code require that manufacturers instructions be followed & the proper way is to torque it to the required torque, and then leave it alone as too much torque is as bad as too little.

[Larry Frank]

I think you should consider Allan Speers suggestion to hire an electrician. At least have one come in and do a quote and find out costs. It is not easy to run heavy gauge wire. If you have not done electrical work before, I think you would be better off having someone else do it for the safety of you and your house....IMHO.

[Ole Anderson]

Am I missing something here? Are we talking about running a 100 or 200 amp panel off another house panel, thereby making it a sub-panel? I don't believe there is a way to pop in even a 100 amp breaker in a home panel, nor would you want to or (I am assuming here) that code would allow it. So that brings up a question, how will you service your new panel? Directly from your meter box? Yes, you need to consult an electrician.

So is it a true 100 amp panel if it is fed from a 60 amp breaker in an existing panel? Isn't that like putting a four cylinder engine in a 3/4 ton pickup?

[Art Mann]

4/0 AL is not rated for 200A, see NEC table 310-16. Edit: The 2014 NEC changed that table to 310.15(B)(16).

Just remember - the National Electrical Code is not the final authority on acceptable wiring. It is written and maintained by a private organization rather than a government agency and does not carry the force of law. Some local authorities require compliance but nearly all make significant changes to it. You can be assured that if you follow it, your wiring will be safe. However, there are millions of houses across the country that are wired to a different or previous standard and they are safe too. The guy who comes out to the house and inspects your wiring is the only authority that really matters because he has the authority to shut you down. Nobody who has anything to do wth the NEC has that authority.

[Art Mann]

Marion, I know you're trying to learn, and that's great. However, if you don't even know the answer to that question, then this is probably a job you need to have an electrician do, start to finish. You don't want to make any mistakes with a 220v line.

I am afraid I have to agree. What you are taking on is far too much for a first time wiring project. Perhaps you can find an electrician who will work with you and teach you what you need to know. A casual conversation with an electrician or wiring inspector is not enough in my opinion.

[Jim Dwight]

I don't know about code requirements but Home Depot sells 100A breakers so that part of it is feasible. I've never worried about what all the breakers in a panel added up to since the main breaker should trip if the capacity of the panel is exceeded. But it would be wise to check the code requirements.

When I had my shop addition done, I saved about half the electricians charge by doing all the finish work myself. I also did the rough in for the outlets in the shop. I had the electrician run the wiring to the heat pump and most of the outlets (non-shop) and all the lights. I did the finish everywhere, and ran the outlets in the shop and my wife's craft/office area. The finish isn't nearly as hard work, it just takes some time. Drilling all the holes in the studs in the shop was harder than I expected. I should have probably let them do that too. 3 way switches are not the easiest but otherwise the finish work is quite easy.

[Brian Hood]

We're mixing up terms here, the OP wants to run a feeder from his single family residence to a sub-panel in his accessory building. He referred to it as a 'service' which it isn't. That size panel will most likely have a buss rating of 125 amps on feeder conductors rated for 80 amps on a 60 amp breaker (depending on his loads). If the total connected load is say 47 amps why jump through flaming rings of fire to install 100 amp overcurrent protection?






Am I missing something here? Are we talking about running a 100 or 200 amp panel off another house panel, thereby making it a sub-panel? I don't believe there is a way to pop in even a 100 amp breaker in a home panel, nor would you want to or (I am assuming here) that code would allow it. So that brings up a question, how will you service your new panel? Directly from your meter box? Yes, you need to consult an electrician.

So is it a true 100 amp panel if it is fed from a 60 amp breaker in an existing panel? Isn't that like putting a four cylinder engine in a 3/4 ton pickup?

[Charles Taylor]

Am I missing something here? Are we talking about running a 100 or 200 amp panel off another house panel, thereby making it a sub-panel? I don't believe there is a way to pop in even a 100 amp breaker in a home panel, nor would you want to or (I am assuming here) that code would allow it.


My workshop is fed by a 100A circuit from the house's main panel. Professionally installed and inspected. As Art and others have pointed out, though, local codes vary, and what was approved in my locale might not be allowed somewhere else.