My shop outbuilding is a powered by 100-amp sub-panel fed by the 200 amp main service to my residence. I’m now adding a gargage 15 feet away from the shop, and want to run power to the garage from the shop.
Do I need to add a breaker panel or disconnect at the garage? Or can I just run a couple of circuits to the garage that have breakers in the shop breaker box?
If I was to add another breaker panel in the garage, how big a panel is too big to still be originating from the 200-amp panel in the residence (via the 100-amp sub-panel in the shop)? I was thinking of adding a 60-amp breaker box at the garage, or alternately just running two or three 20-amp circuits straight from the shop breaker panel to the garage.
Steve
Edited 10/24/2009 11:16 pm by mmoogie
Replies
The most recent NEC copy I have is 1980, so if you want to 'do code' will let others answer.
However, from a practical safety point, as long as the source breaker protects downstream wires from overcurrent you are good.
Either of your options mentioned are OK - 60A breaker at shop feeding 60 A panel in garage or the 3 separate 20A breakers in the shop feeding the garage.
Some code purists likely want a disconnect in the garage, but only 15 ft away?
Just for convenience I'll probably go with a breaker panel or a disconnect switch in the garage. While the buildings are only 15 feet apart, the door into the shop is about 40 feet from the door into the garage. I was thinking about running the 3 loose circuits for ease of pulling 12 gauge wire rather than 6-gauge, but I'll probably bite the bullet and run the 6-gauge to a sub-panel.If I recall I have to run two ground rods for that panel if I want to bond the neutral and the ground in the panel. Is that right?Steve
My understanding of current code since about 1990 (and someone may be along to correct me) is that if you have a separate structure that needs multiple circuits, it must (to meet code) have it's own subpanel. Of course, stuff installed before this code change hasn't, for the most part, all burned down, so the safety difference is probably negligible.
Dunno if there's any rules regarding the size of the panel.
A separate structure generally needs it's own disconnect.
There is also the issue of 'derating' the wires when there is more than on circuit in the same pipe.
While not specifically 'required,' having a separate panel in the building makes things a lot easier - both now, and later, when you want to add more.
There's no reason the garage panel can't be as large as 100-amp, coming off that other 100-amp panel.
However you do it, you will still need a ground rod at that separate garage.
Single ground rod and the neutral and ground must be separate, right? Two ground rods and they can be bonded, yes?
You've got it half right.
Separate the neutral and the ground, run that fourth wire, no matter what.
One ground rod is the NEC minimum; some locations require a second, just to be sure there's a goos connection.
In simple terms, the ground rods are for lightning - while the fourth wire is to make sure breakers trip. Two completely different concepts.
You can't run multiple circuits to a detached building (with a very few exceptions that seldom apply to a residential setting).
Run a 4 wire feeder and set a sub panel with a disconnect and a grounding electrode system.
Thank you for the correction.
So I've pulled 4-wire feeder between the two buildings. Looking more closely at the first sub-panel, I see they only pulled 3 wires from the house to the shop. Neutral goes to neutral bus, One bare wire from grounding rod(s?) goes to ground bus. Ground and neutral bus are tied together. I haven't looked closely to see if there are one or two grounding rods.So hooking up my 4-wire to the next sub-panel I should run the ground wire from the ground bus in the shop to the ground bus in the garage, neutral wire from neutral bus in shop to neutral bus in garage? Plus I should install 2 ground rods six feet apart, wire them together and run one ground wire from one of the ground rods to the ground bus in the garage? And I should leave the ground bus and neutral bus tied together at both sub panels?Steve
They are tied together at the existing panel, separated at the new panel.
I'm kind of wondering why are they tied together at the existing panel.Steve
THE ONLY PLACE THAT A GROUND AND NEUTRAL CAN BE TIED TOGETHER IS AT THE MAIN PANEL. THEY MUST BE KEPT SEPARATE AT ALL SUB-PANELS.
Since you used all CAPS <g>
Unless in some critical military installations, everything tied to the closest ground or metal silo liner for EMP protection.
Wow sorry about the caps my lock was on.As for separating the subpanel grounds and neutrals, Thats just the way I was taught.Sorry.I'll do more research.
The problem with that LOUD STATEMENT is, until the 2008 code, you could run a 3 wire feeder to a detached building and reground the neutral.
So I'm guessing I should keep the ground and neutral separate on the garage subpanel. Is there anything I need to worry about on the intermediate panel with the three-wire feeder and the tied ground and neutral?Should I still ground the 4-wire-fed garage panel to ground rod(s) even though the neutral and ground will be kept separated?Steve
You hook the ground rod to the ground bus, the Neutral stays isolated from the panel and the ground..This is not a huge problem but Ryan Jackson proposed that they change the code so it would be consistent.
Sorry about being loud my caps was locked. I always was told to separate untll the main. i'll do some more research.
>>>until the 2008 code, you could run a 3 wire feeder to a detached building and reground the neutral.Interesting. Looks like the Canadian and American codes are once again in sync (darn things are always a moving target). Since I've been doing electical work (about the last 12 years), I've always had to bring the bonding conductor back to the main panel, and it's led to some confusion with postings here.The only exception that I know of is animal barns. I was once told by a long-time inspector that milking cattle are very sensitive to electrical energy. One solution was to re-ground the neutral in barns. Are there any exceptions in the NEC?Scott.
Milking cows are sensitive to day light savings time also. Thats why we don't change :)I have milked a few and they can hurt you pretty fast if not on routine. They don't like change, like a horse running threw the barn with a Red Heeler in pursuit.
>>>They don't like change, like a horse running threw the barn with a Red Heeler in pursuit.Hahaha...Now there's an analogy. I guess the horse and the heeler just like to keep on running....
There are special rules for livestock buildings. But I have need to know them so I don't.But I think that it is more like pools. The intent is to get an equal potential plane around the barn..
William the Geezer, the sequel to Billy the Kid - Shoe
There's little point getting all excited about grounding ... over the years our understanding of the topic has changes, as we learned more. Unfortunaltely, majorr parts of the electric code were written to an earlier, different, set of assumptions, with the result that Article 250 (grounding) was even more obtuse and contradictory than is usual for the NEC.
In 2005 a major edit of this section cleaned up a lot of the mess; 2008 addressed the OP's specific situation. Before 2008, it was possible to find code language that allowed the OP's original installation. Bad practice and bad code.
Oddly enough, anyone who went through a proper apprenticeship, since the 50's at least, was taught the 'right way.' It was another case of where following 'trade practice' met, or exceeded, code .... but designing 'to code' often got you in trouble.
That said, the OP was dealt a bad hand in his original construction, and I think he knows that. His question was 'how do I do the new stuff right?'
Unfortunately this is all pretty recent work. The house panel is no more than 20 years old. SquareD QO 200 amp, that was in place in this 190 yr old house when I bought it. It was installed by a licensed sparky before I bought the place. The first sub-panel was installed just a couple of years ago by another licensed local electrician who does a lot of work around here. I ran the plastic conduit from the house to the shop and he pulled the wires and did the panel hookup maybe three years ago. I paid for a licencsed sparky because I know I'm over my head on the big stuff. I've done all the wiring inside the house and inside the shop.Is there anything inherently dangerous about the hookup of the first sub-panel? To recap: 3 aluminum wires...neutral and two hots...running through plastic conduit about 200 feet to the shop, where ground rods are driven to provide a ground wire. Neutral and ground bus are tied together and bonded to the box.Should I change anything at this point? I'm about to call the inspector for clearance on the rough-in. The shop is all wired and I've been using it for a couple of years now. I want to close it all up and insulate, plus get the garage wired up.Steve
Having the feed to the panel in plastic pipe greatly reduces the issue; if the opportunity presents itself to get a separate ground wire in the pipe, take it - but I wouldn't lose sleep over the issue.
Here's wher the problem arises:
In a proper installation, there is only one point where the neuutral is bonded to the ground. Current in either wire has only one place to go: into the utility neutral. Get too much, and a breaker will trip. All is happy.
Now, let's carry the example to a house with two panels, and the neutral is bonded to the ground at both panels. Everything is happy, and everything works - for now. This does not mean that everything is fine, though.
In this imaginary home, let's say each panel is supplying a water heater, and the plumbing is bonded at each water heater. Now you have TWO paths for neutral current to take back to the 'main' panel. Current can flow through the neutral wire that you have run between the panels, as it's supposed to. Current will also always be flowing from the 'sub'panel' neutral, into the ground wire, through the plumbing, into another ground wire, and thus back to 'main' panel. You've just turned your plumbing into another neutral wire - open a fitting, and one side may become "hot."
I think you can see where this can be a bad situation.
If you only see 3 wires (two hots and a neutral) entering the sub from the main panel, odds are the sub feeder is in greenfield and they have a mechanical ground. Netutral bar in the sub should be isolated from the panel and the ground bar. Ground bar should be bonded to panel. Same set up in new panel.