I am moving into a new (rental) house with a separate workshop building. The shop currently has 3 wires running from the house. The Owner is having the house electrical totally replaced (100A), and she offered to have a new service line run out to the shop. Once inside the shop, electrical work is my responsibility. It is a very old building, and the electrical currently consists of an impossible web of cloth wrapped wire running between bus fuse boxes and bar fuse boxes that it appears were used as on/off switches(some of them have pieces of wire soldered where the fuse should be). I have decided it is best to tear everything out, and start from scratch.
My Questions are:
What are the 3 wires? (hot, neutral, ground?)
Should the shop have it’s own ground?
How large a breaker should I tell the landlord I need installed in the main service panel? I will be running 800 watts of lighting (10 80w fixtures)and all of my tools are currently 120.
I plan on buying a 230v tablesaw in the near future, will the 3 wire service offer the correct power to run it?
Anything else I need to know?
Thanks for sharing your expertise!
Tony
Replies
Hi Tony,
I'm not an electrician, but I have wired my own shop from the breaker panal out.
My first impression was why is the homeowner only putting in a 100A service panal? A 200A panal is much more common, and would allow a 100A subpanal in the shop.
Your present feed is most likely two hots and a ground, and yes, your panal should have its own ground stake as well. And yes, I would tear it out and start over.
Also, consider having a qualified electrician install the shop subpanal at the same time the house service is upgraded. The additional cost should be minimal, and certainly cheaper than if you hired it out separately. Then you can wire the shop from the panal out, confident that the service is up to code and safe.
Tom
Tom
Regarding Amperage:
The house is in a rural area and is very small, and apparently the service lines running from the road can not handle more than 100A. The owner did not want to pay to have them replaced.
Thanks
Tony
Hi,
I recently did something similar in an old industrial building I bought for my shop. Replaced the fuse boxes with a circuit breaker panel and pulled new wire through the conduit. I use a minimum wire gauge of 12 instead of 14.
Also, grounding requirements have gotten stricter over the years and more rather than less is a good thing, so yes I would suggest a ground rod for your building and panel.
You might want to pick up Tauntons book "Wiring a house" it is well written and will help answer many questions.
I would think that your service would handle the 230v tablesaw provided the line installed to your building is properly sized. Will this work be
inspected?
Good luck,
Tom
Almost certainly the service coming from the street is 120/240volts, single phase. There will be two hot wires and a neutral (you get 240volts between the two hot wires, or 120volts from either one of the hot wires to the neutral.) The house will be grounded at the service entrance point.
I agree with the others that it's probably best to have the electrician extend the branch circuit from the house to the shop, and then have him install the subpanel at the shop.
The short answer for the breaker size is to get the largest one you can, but since the owner isn't going to spring for a 200 amp service to the house it'll probably limit what you can do for the shop.
The house is going to use a certain amount of that 100 amps but from this distance we can't tell you what that will be...does it have a lot of electrical loads, like a stove, water heater, baseboard heat, air conditioning, etc.? Probably the only thing you can do is talk to the electrician who's going to do the work. He should be able to figure out how big you can go.
Given the level of expertise you seem to have, I'd get an electrician at least as an advisor (if he's willing. Many are not because of liability.) Exterior wiring and panel, certainly have this done by an electrician. You will need ground rods. Sizing the panel and the drop wire is not quite an amateur job. Chances are that you'll end up with a 60 amp subpanel. You won't actually draw 60 amps. Most likely about 20 but you may run space heaters or other stuff and you need some margin.
What the existing 3 wires are could be anybody's guess. Depends on when they were installed and by whom. Could be hot, neutral, ground. Could be hot, hot, neutral. There may or may not be a ground wire at all.
Interior wiring is not as difficult. I'd wire the lights as 2 circuits. 15 amps each - #14 wire. That way you can shut down one circuit and work on it without turning off all the light. I'd do probably 4 20-amp outlet circuits. 12-gauge. Each with 3 or 4 duplex outlets. And, one 220 volt 30 amp circuit with a 4-wire dryer socket for the table saw. Those cannot be chained. One outlet per duplex breaker. That would be 10-gauge. You may want another for a dust collector. You may not be required by code to use metallic sheathed or conduit, but I'd do it. It provides mechanical protection so you won't have problems if you whack a cable with a board or something. Around here, plain romex can be used in outbuildings. Metal conduit is good. Expensive, but good. Metallic sheathed is second choice. Easier to run but has its own issues. The fittings and technique vary with all options. Find a good book and read it as your first step.
Thanks for the input everyone. I plan to have a pro do the major work, I just am trying to get an idea of what the job should entail before I start making phone calls.
Residential wiring is not all that complicated. It is always best to hire an electrician.However, years ago when I set up my shop, I found an old, retired electrician, and paid him (in cash) to be around and advise on what I should do and how. His knees were gone (could not even climb a ladder), and he seemed to enjoy sitting around the shop and imparting his knowledge. He was beyond caring about liability or union issues. Along with a lot of reading, it was great to have him around to teach me all the little tricks that don't seem to find their way into books.
Tony,
The three wires coming into the outbuilding could be configured to be anything you want, it just depends on how they are hooked up on the feed side. If one of the three wires is bare then that one can only be used as a ground, but the other two, presuming they are insulated, could be wired so that they are both hot for 220/240 volt service or they could be one hot and one neutral, which would give you 110/120 volt service.
The real problem is that for a new panel you would really need four wires coming in, two hots, a neutral, and a ground. If the wire coming into the shop building is only three wire, then you won't be able to have both 110 and 220 volt service without installing a new line between the house and the shop.
Also if the wire coming out to the shop is a small gauge, like a number 12, the maximum load it can carry will be limited to 20 amps. A 14 gauge wire would limit you to 15 amp service. The size of the breaker in the house panel serving the shop is strictly determined by the size of the smallest wire in the circuit. You can easily change the size of the house and shop wiring, but the breaker size will then be dependent on the size of the feeder cable to the shop if that can't be changed.
My guess is that the feeder is probably a small gauge meant to serve just a few lights and it won't be adequate for the upgraded service you are planning for.
John W.
The real problem is that for a new panel you would really need four wires coming in, two hots, a neutral, and a ground. If the wire coming into the shop building is only three wire, then you won't be able to have both 110 and 220 volt service without installing a new line between the house and the shop.
Not necessarily true. If the feeder is running to a separate building, and there is no other metallic path between the buildings (e.g. metal plumbing pipes), then it's possible to use 3 wires, as an option under the NEC. In this case, the subpanel in the outbulding is treated as a main panel, with the neutral wire from the main panel grounded at the outbuilding, and bonded to both neutral and grounding branch circuit conductors. See NEC 250-32(b)(2).
As to the original poster, these questions are such that it seems you have a bit of learning to do. Get a book on wiring.
Also, anyone doing any wiring should have a copy of the NEC, available at http://www.nfpa.org. Good indicator of whether you know enough to do your own wiring is if you can read and understand the NEC.
I was aware that there were options, but I couldn't cover all the possibilities without starting up a small course on advanced wiring for pros. I merely tried to cover the most likely scenario and the simplest solution.
Again this is gut level instinct, but if the entire house needed to be rewired and the shop has funky post and tube wiring, then the line from the house to the shop probably isn't in good shape, probably has too small a capacity, and not enough conductors, and will have to be replaced along with everything else.
John W.
Edited 1/19/2005 2:15 pm ET by JohnW
The landlord is going to spring for new lines out to the shop, so I asked her to tell the electrician to run hot,hot,neutral, and I will drive a ground spike.
I think that because the shop is a detached building, the subpanal will be considered a new service. That most likely means that you will need two grounding stakes twelve feet apart.I'm not an electrician, so as someone else suggested, you might want to look it up in the NEC. On the other hand, since you have a qualified electrician installing the subpanal, I don't think he can leave the grounding stake for the homeowner/occupant to install. He will want to be sure that what he leaves is up to code, when he leaves it.Tom
Whether or not you run 3 or 4 wires, as a separate building, it needs its own grounding electrode system. Around here, inspectors want 2 electrodes, at least 6 feet apart.
Where I live, I don't think you can even pull a permit for 100 amp into a residence. I think the minimum is 150.
Subpanel is the way to go for sure. I'm practically positive that any such installation will have to have a permit pulled and the work inspected and approved.
You must have one great (or extremely shortsighted) landlord to let you do this work yourself if you aren't a licensed electrician.
No ifs, ands, about it....HIRE AN ELECTRICIAN!!! You won't regret it. Best of luck...Jimmy.
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