a few service questions

[jonese]

1) I've read a lot of threads with people asking how large a panel they need and everyone says that 100amp is plenty. I went to the local building supply store and asked the guy what I needed and told him I'd have a welder or two and he recommended I go with a 200amp panel. I was looking at a mig, something like the Hobart 125 or 140. If I'm not mistaken those numbers relate to the amperage of the units so how could a 100amp service be adequate?

2) I've been told it would be smarter to run the service from my house to my detached garage rather than getting a new meter to the garage. It would probably be just as much work either way so there's no advantage there. The thinking is that if it had it's own meter the electric company would charge me a minimum monthly fee, maybe $20-30 even if I didn't use that much electricity. So there's some cost savings there. The problem is I had an electric tankless hot water heater installed in my house when it was built about four years ago and the contracter had a fit saying the wiring in the house wasn't large enough to handle the load of the water heater. It ended up working out but what I'm wondering is if there's enough juice left to power my garage if the hot water heater draws so much current when it's on. I do notice the lights dim in the house sometimes when the water heater is on. How do I check to make sure I can run service from my house to the garage?

 

[jonese]

Re: a few service quiestions

Just to give you all an idea of the tools I will have in the garage I'll have something like a 60gal 5hp compressor, a mig welder, possibly a tig in the future, a bandsaw, grinder, belt sander, sand blast cabinet, and a two post lift, plus fluorescent lighting.

 

[brewchief]

Re: a few service quiestions

1) I was looking at a mig, something like the Hobart 125 or 140. If I'm not mistaken those numbers relate to the amperage of the units so how could a 100amp service be adequate?

That's output amperage not input, I've got a Hobart 210 and IIRC the max input is 26-29 amps.

 

[jonese]

Re: a few service quiestions

Oh cool, that mystery is solved then. I think the air compressor at about 20-22 amps and the welder which apparently will be less than 26 amps will probably be the biggest current hogs so I think 100 amp service will be more than enough. Thanks.

The other thing is do I really need 6/3 NMWG like the guy at the hardware store recommended? It'll be about a 75 foot underground run.

 

[Neuswede]

Re: a few service quiestions

If you are only 1 guy in the shop, you can do alot with 100 Amps. Your welder will not be running continually, and more than likely the only conflict might be having a large air compressor kicking on while welding. It takes alot to use up 100 Amps.

It's all the other stuff that can add up, like heat, hot water, air conditioning, and lighting. BUT, you need to very quietly find out what the local utility will allow you to do. DO NOT talk to them directly about welders or any motors over 1 HP until you talk with an excellent local electrician about what you can and can't do. I made the FATAL mistake of mentioning this while I wanted 320 service, and I've been fighting since May 31 just to get approval from the bastards. They tried selling me $2,600 worth of transformers and **** that by their tariff they are obligated to pay, and now that I called them on it, we are at a Mexican standoff and they are burning up any remaining time I have left in this season to get the conduit in and get the mud covered up. If you are lucky, you can find your utility's state filed tariff and their installation guidelines on their website..then talk with an electrician. In my particular case, the utility had a fit that I wanted to go to the garage first, have my disconnects and future backup generator, then run the main service back to the house. Both my electrician, electrical inspector and the building code official had no issues with this layout, but the utility now has a huge hair across their *** over being told that their way is not how we are going to do it.

If you are lucky, you have a cooperative utility; mine has one of the worst reputations in the east (Met-Ed/First Energy), and they live up to it daily. Be careful....be very careful.

 

[BigJohn20]

Re: a few service quiestions

What tankless hot water heater do you have installed? On some of those units, they can run over 100A/240v.

When you say run service to your garage, are you talking about getting a meter with double lugs at your house and then having two separate main breaker panels, one in the garage and one in the house? Or are you talking about just running a subpanel to the garage?

Either way, I would highly suggest you use a load calculation worksheet to get an idea of what size your service should be.

100A for all of that gear seems pretty low, mostly due to the electric tankless hot water heater.

 

[BigJohn20]

Re: a few service quiestions

Oh cool, that mystery is solved then. I think the air compressor at about 20-22 amps and the welder which apparently will be less than 26 amps will probably be the biggest current hogs so I think 100 amp service will be more than enough. Thanks.

The other thing is do I really need 6/3 NMWG like the guy at the hardware store recommended? It'll be about a 75 foot underground run.

NM-B cannot be installed underground, period. You either need to use THWN (or similar) in conduit or UF.

 

[jonese]

Re: a few service quiestions

NM-B cannot be installed underground, period. You either need to use THWN (or similar) in conduit or UF.

Yeah I did some searching around and found this somewhere. I guess that stuff can't get wet and conduit will collect water so I'm not sure why that's what was recommended to me.

I don't really know a lot of the nomenclature for electrical work but what I think I want to do is run a 100amp sub panel to the garage but there would still be a breaker box in the garage as well wouldn't there?

The water heater is a tempra unit. On the side it reads:

27.0kW single phase AC 208V 60Hz 130A
36.0kW single phase AC 240V 60Hz 150A

I'm guessing that means it'll draw between 130 and 150A but I'm not sure what that tells me because it still depends on how much current I'm using for other stuff. I'm pretty sure I remember seeing a 200A panel on the house but I'll have to check again.

 

[BigJohn20]

Re: a few service quiestions

jonese,

If people sound condescending, it's because this is a much, much bigger job than you realize. You can't just run a subpanel to your garage at this point. You have some serious load issues that need to be dealt with.

Most likely, you'll need to upgrade your main service to a 400A non-continuous/320A continuous service. A common way to do this is to get a 400A/320A meter socket with dual lugs, main disconnect, and run two main breaker panels. Be warned that the 400A meter sockets are quite a bit more expensive than a standard 200a meter socket. You will need to get your power company involved in this.

Running to the garage, if you want a 100A subpanel, you'd need 2AWG Cu wire for 100A subpanel. Over a distance of almost 100ft from the main panel, I would suggest going with heavier 1AWG Cu wire.

At this point, you NEED a licensed electrical contractor. He needs to do a load calc, and will tell you everything that needs to be done. This is way, way outside the scope of a DIY project. After he gets the main service to your house done, then you can worry about running a subpanel out to your garage.