Electrical code

[Shran]

Does anyone have access to the up-to-date NEC code book and/or do we have any electricians on the site?

I have two electric meters on my property, one old one on the house (100 amp, overhead service) and a new one on my shop (200 amp, underground.) I want to subfeed the house off the shop and remove the old meter and overhead line and replace it with buried cable (roughly 100'.) This will clean up the place a lot and save me $10/month for the extra meter. It is a relatively simple project but I am getting quotes of around $6000 so I'm considering doing it myself.

I'm fairly familiar with AC wiring, I have rewired about half my house and my entire shop. I am not as familiar with how they want the new feed from the shop to the house to look - one quote I got said that it includes a 125A breaker, one unmetered disconnect, and "125 amp underground wire" whatever that means, what wire size is my question.

I'm assuming they'd run wire from the 125A breaker outside to the disconnect box, then from there to the house where the old meter can is?

 

[franklin2]

125 amp tapped off a 200 amp service is getting up there. Can you get by with 100 amp to the shop? Or even 60? Granted I have a small shop, the largest draw I have is a welder and it pulls 40 amp on a 220 double pole breaker. It does fine with the 60 amp service I have. I have a decent sized compressor and a 8000lb vehicle lift. It all does fine with the 60. You have to realize you are only one person, so you most likely will only be running one thing at a time.

The reason I asked about your amperage needs, lower service amperage means lower cost, especially with the wire.

What size and type of panel do you have in the garage now?

You can run aluminum direct bury wire, it's cheaper. But I would still run the wire in PCV pipe, the pipe is good insurance against rocks poking the wire.

Around 100 ft is the max length before you should upsize your wire for voltage drop. If you do not have a tremendous load in your shop, you will be good anyway.

Here is a link to a NEC wire chart. It says 2002 but it hasn't changed in years.

https://www.usawire-cable.com/pdf/nec-ampacities.pdf

#2 copper is commonly used for 100 amp services. #2 aluminum will work also if you are using the higher temp wire. Most wire you buy now is THHN which is the 90 degree wire. It's always good to check that though. You would need to go one size larger for 125amp.

What is important is running a separate neutral and ground wire to the shop from the house. And you will have to re-wire modify your shop panel more than likely. NEC will only allow you to hook your neutral (white) wires and your ground wires together in one spot. That will be your house panel. Any sub panel after that (which your shop will become) has to have separate neutrals and grounds.

You will have to go to Lowe's and buy a ground bar, and mount it in the shop panel directly to the back of the metal panel. And there may be some more modification to make sure the large neutral wire and neutral bar in the shop panel is not bolted to the metal box of the panel. You will then need to take all your ground wires off the neutral bar in the shop panel and move them to the new ground bar. And then your large ground running with the other new wires from the house will hook to the new ground bar in the shop.

 

[Shran]

I'm not concerned with wire cost although I was planning on running aluminum direct bury wire in conduit like you said. I have about 90' of driveway between the house and shop plus another 10' or so on either end to go up and into each panel.

I can get by with 100 amps in the shop, I think. I have 5 or 6 110v, 15A circuits for wall outlets and lights plus one 30A, 220v and one 50A, 220v and will probably add one more 110v circuit for a shop heater fan at some point. The 220v circuits are used for a compressor and a welder. Compressor is used a lot, welder not as much.

The house really needs not much power as it is now. I have all gas appliances except the dryer (30A 220v circuit.) There are I think 6 or 7 other 110v, 15A circuits in the box plus two 20A 220v ones that were for window AC units - I could abandon those or maybe use those spaces in the panel for central air if I ever install that. 100A to the house is more than enough but as I understand the quote, it has to be upsized to 125 amp since the house will be sub fed off the shop.

Think I've got an Eaton 30 space 200 amp panel in the shop and an older (15-20 years old) GE 100 amp panel in the house.

NEC will only allow you to hook your neutral (white) wires and your ground wires together in one spot. That will be your house panel. Any sub panel after that (which your shop will become) has to have separate neutrals and grounds.

Isn't that backwards since the house will be sub fed off the shop?

 

[Bronco648]

I'm sure you have multiple quotes for the work and have narrowed it down to just one or two contractors, at this point. Perhaps you can inquire about ways to lessen the cost of the job without "stepping on toes". All contractors will warranty their work and may not be willing to allow you to do some of the job for fear your work might be sub-standard (no offense). However, if you're willing to do the 'grunt' work, they may be OK with it. Ask if you can dig the trench and run the PVC conduit and wire from the house to the shop. Ask them if they'd spec the conduit and wire. Then, all you've done is the work some apprentice would do and perhaps you've saved yourself $1000+. It never hurts to check.

 

[Bronco648]

Isn't that backwards since the house will be sub fed off the shop?

I wonder if the wiring could be re-done such that the main feed is into the house, @ 100 amps, and then sub-feed the shop. That way you might be able to get around the 125 amp requirement.

You could consider getting a gas dryer to further reduce the load on the house service. It doesn't have to be something new, plenty of nice used gas dryers out there.

 

[Shran]

That was my first thought several years ago when I started wiring the shop, however, I only have 100 amp service from the power pole at the house now. None of it is up to code, the meter is 10' off the ground, and aside from the newer breaker panel, a lot of the wiring in the house dates back to the 60's or earlier. As I understand it, if I have the house fed off the shop, I can keep my house panel intact and simply remove the meter, mast, etc from it and power it from my new underground feed and pass inspection.

If I fed the shop off the house, I would still have to dig a trench, update the panel and service to the house, and the same amount of wire, disconnect, etc... at this point it is simply easier to feed the house from the shop.

This is what the whole deal looks like:

 

[Bronco648]

OK, I understand. Regardless of what you do it seems as if there are new codes issues with which to deal. Your way sounds easiest.

 

[RonD]

The main thing is each building needs its own Disconnect, thats a big deal for the Code

And then the wire gauge vs distance and amps, also depth of trench, and for sure inside a pipe.
There are trenchless ways to do this under paved driveways

You can do it all yourself, but...............insurance companies can get a bit picky, lol, if there is a fire and homeowner installed wiring was a factor
Was the wiring you did in the house and/or shop terminated by an electrician?

 

[franklin2]

Boy I had it totally backwards, I don't read carefully enough. You are going to have the house be the subpanel not the shop.

What I would do is pay someone to install the 200 amp panel in the shop. The electric company around here won't put power to anything that has not been permitted and inspected. So once you get someone to install the new panel in the shop, you can go and do your own thing and all the work for the shop to the house. Leave the old house service up a little longer till you are ready, then there is no pressure.

Once you are very close to getting power to the house, tell the elec company to come out and disconnect that service and get rid of it. I am not sure if they will charge you or not for this. For any upgrades around here, it is free. Your shop is a upgrade. Tearing things out for no reason, they might charge a service fee. Check on this.

Once the old house service is out of the way, you can hook your new power from the shop to the house, done.

Check with the power co and see how sticky they are about applying power to a new service during a upgrade. If they don't care, I would do the whole thing yourself.

 

[Shran]

The main thing is each building needs its own Disconnect, thats a big deal for the Code

And then the wire gauge vs distance and amps, also depth of trench, and for sure inside a pipe.
There are trenchless ways to do this under paved driveways

You can do it all yourself, but...............insurance companies can get a bit picky, lol, if there is a fire and homeowner installed wiring was a factor
Was the wiring you did in the house and/or shop terminated by an electrician?

10-4 on the disconnect, was planning on that, just wasn't sure if it had to be fed from my shop's breaker box, or straight off the meter, or what.

I have a gravel driveway so no big deal digging through it with a trencher, it'll be easy to fix.

We can get homeowner's wiring permits (I have one in hand.) Once the work is roughed in, we just call the local inspector and they come out and look at it - if it looks good then they sign off and it's as good as an electrician's work. That's what I did for the house and shop, they were inspected on a previous homeowner's permit after I did the work.

Boy I had it totally backwards, I don't read carefully enough. You are going to have the house be the subpanel not the shop.

Ha, correct, the house will be the sub panel.

What I would do is pay someone to install the 200 amp panel in the shop. The electric company around here won't put power to anything that has not been permitted and inspected. So once you get someone to install the new panel in the shop, you can go and do your own thing and all the work for the shop to the house. Leave the old house service up a little longer till you are ready, then there is no pressure.

The shop already has a 200 amp panel installed, the whole building is wired and complete at this point and has been for a couple years. I am simply adding the additional breaker, disconnect, and feed from there to the house.

Once you are very close to getting power to the house, tell the elec company to come out and disconnect that service and get rid of it. I am not sure if they will charge you or not for this. For any upgrades around here, it is free. Your shop is a upgrade. Tearing things out for no reason, they might charge a service fee. Check on this.

That's probably what I'll do... all they have to do is come out and unhook the house and take their meter, probably all of about an hour and I'm sure it's free. It'll be a good deal for them because they won't have a 50 year old overhead line to deal with ever again.

Once the old house service is out of the way, you can hook your new power from the shop to the house, done.

Check with the power co and see how sticky they are about applying power to a new service during a upgrade. If they don't care, I would do the whole thing yourself.

I don't think they really care as long as it has passed the rough in inspection.

My boss was an electrician years ago and I'll probably have him give me a hand. I would ask him about all this but his knowledge is 30 years out of date and some stuff he told me to do before was not up to code now so I want to get my ducks in a row before I buy anything.

 

[ericbphoto]

Not a bad project. I would install the 125amp breaker in the shop panel. Run your cable/conduit 24" deep. That's the requirement for going under the driveway. Then come up and replace the meter panel on the house with the 125amp disconnect which then feeds into the house breaker panel. They will probably still want you to tie the house to a ground rod at the house. BUT, the ground and neutral will NOT be connected to each other anywhere except where they connect at the shop - probably in the meter can.

I'm 99.99%sure that would pass inspection here in SC. I do hold a current master electrician license. Though I haven't built a service for inspection in the last few years. Even if there is a detail wrong there it will be minor and easy to fix.

2AWG copper or 1/0AWG aluminum. If I were you, I would go to a local electrical supply house. Tell them what you are doing. Ask for "1/0 aluminum triplex SEU cable. That will come with the appropriate sized neutral conductor. You should also get 8AWG copper ground wire to go with that. Though in some areas, they require minimum 6AWG copper for the ground. I would put it all in 1 1/2" PVC conduit. It will fit in 1 1/4" but the larger pipe will be easier to pull through because of the larger radius bends. Get a small container of pulling lube. It's messy. But makes the job easier.

After your conduit is installed, tie part of a plastic grocery bag to a spool of nylon string. Stick it in one end of the conduit in such a way that it fills the pipe but isn't too tight. Then use a shop vac from the other end to suck it through. That will give you something you can use to pull a 1/4" or 3/8" rope through to use to pull your wire through the conduit.

 

[ericbphoto]

Here's a similar project I did years ago. Except the "6 bay shop with apartment above" was sub-fed from the house. The meter panel on the house had a loose connection inside and was buzzing and melting when they called me. I replaced that , upgraded the whole service to 350amps and added the disconnect to feed the shop/apartment all at one time.

 

[franklin2]

BUT, the ground and neutral will NOT be connected to each other anywhere except where they connect at the shop - probably in the meter can.

Yep, that is what I mentioned before only I though the subpanel was the shop. So more than likely you will need to do a little re-wiring in the house panel to separate the grounds and the neutrals. I think I mentioned before, places like Lowe's and electrical supply houses sell ground bars that you can custom mount in the panel box to separate your white wires from your grounds.