Hi all,
I just helped a friend rewire his garage and the subpanel we bought did NOT have an isolated grounding bus, so we tied the returns and grounds together on the same bus. I know that in subpanels you are supposed to separate these two and only combine them at the main. I did check the potential between the grounds and returns and found it to be zero in every case.
The subpanel will be too difficult to remove now (fastened into concrete) so I’d like to know how to isolate a separate grounding bus. The grounding bus itself is readily available, but how does one attach it to the box to isolate it? A plastic stand off with epoxy was the first thing that came to mind, but I’d rather do it in an approved manner.
This is a 6-space Square D surface mount panel, lugs only.
Thanks!
Jim
Replies
Does the existing neutral bus (on the sub panel) have a green ground screw? If so, remove it. Then install grounding bus by screwing directly to metal panel (inside - duh). Run a separate ground from main panel directly to new grounding bus on sub panel.
The neutral bus at the sub panel should NOT be grounded to the metal box of the sub panel. It is the grounding bus that should be. And this is generally taken care of simply by screwing it to the inside of the panel. Typically holes are already available. Just make sure they have no plastic isolators. You WANT the grounding bus to make contact with the panel box.
This is my understanding, and am rather certain I am correct. However, I am not a licensed electrician (I'm an archy). Others here are, and can probably confirm/clarify further what I have outlined.
The only "approved manner" is what the manufacturer recommends. If you do something not recommended by the manufacturer, it's a code violation.
Check with Square D, or the dealer in your area. They'll show you exactly how to do it for the panel you have, and will supply the right parts if they're missing.
Well darn it. I read your post and tried, tried, tried to refrain from commenting. But I cannot help myself.
First, let me say I agree completely that it is wise to contact the manufacturer for additional information. Just be careful of who is on the other end, and measure their "advise" accordingly (just like here at BT).
Second, regarding: "If you do something not recommended by the manufacturer, it's a code violation." When was it that building codes started being written based upon manufacturers recommendations? Isn't it possible that you could still be in full compliance with the building code (UBC, NEC, etc) and still not comply with manufactueres recommendations? Seems to me that what you may achieve, however, is voiding the manufacturers warrantee. Like I said, I tried to refrain...
"Second, regarding: "If you do something not recommended by the manufacturer, it's a code violation." When was it that building codes started being written based upon manufacturers recommendations? Isn't it possible that you could still be in full compliance with the building code (UBC, NEC, etc) and still not comply with manufactueres recommendations? Seems to me that what you may achieve, however, is voiding the manufacturers warrantee. Like I said, I tried to refrain..."
Here are a couple of sections out of the NEC.
"Suitbility of equipment usage may be identified by a descreiption makred on or provided with a product to identify the suitability of the product for a SEPECIFIC PUROSE, environmental, or application. Suitability of equipment maybe evidenced by listing or labeling."
"Listed or labeled equipment shall be installed and used IN ACCORDANGE WITH ANY INSTRUCTIONS INCLUDED IN THE LISTING OR LABELING".
If you did not have that you wouldn't have anything. The code does not call out the spec's on anything.
OK, I get your point. And GENERALLY speaking (especially with respect to electrical and mechanical equipment) one probably would be in violation of the code(s) if they did not follow the manufacturers recommendations. I do not suggest that someone use or modify a piece of equipment for other than its intended use, and especially if it could create an un-safe condition.
My response to the original post (malibujim) was because I thought that he didn't quite have the concept of isolated ground correct. Perhaps I don't either, which is why I qualified my response.
Perhaps I read the comment about mfr's recommendations vs. code violation out of context. It struck me as a pretty strong statement that while generally true, is possibly missleading. I still contend that not following "all" manufacturers recommendations does not necessarily force a violation of the code. A lame example (non-electrical) would be a siding manufacturer recommending stainless steel fasteners. While it may be a "good" recommendation, it would not be a violation of the code to use galvies, etc. Or, what if a panel manufacturer recommends using a panel with copper stabs for exterior use. Does that mean you couldn't use one with aluminum (so long as it wasn't specifically prohibited). My point being a recommendation is exactly that, a recommended way. It is not necessarily the only way. Now manufacturers instructions, and specs, that's different. Not following those would make for a fool. Gotta run and pick up DW at the bus...
I'm sorry I wasn't more clear. You are certainly right that, in general, following manufacturer's recommendations is not required by building codes. What I did not say was that National Electric Code requires that electrical equipment be installed according to manufacturer's instructions in order to be permitted under the code.
So trying to modify an electrical panel with epoxy and plastic would not be permitted under the NEC.
I should not have come across so dogmatically.
You wrote "When was it that building codes started being written based upon manufacturers recommendations?"
Well, I'm sure exactly when; but, the NEC is written by (or for, depending on how you want to roll semantics) the electrical manufacturers..
Phill Giles
The Unionville Woodwright
Unionville, Ontario
As an aside;
I came across the same situation a while back and, thanks to many readings including the FHB feature, I am relieved to hear that I dealt with the situation correcly.
However, in my situation, the subpanel was 240' away from the main and my local big box store didn't sell any bare copper ground wire of any size in rolls that long. I'm sure I could have found it somewhere, but they did sell 8 guage wire with the standard insulation in 500' rolls. I used that because I couldn't think of a logical reason why not to. If it's standard to be bare, why couldn't it be insulated, after all?
I used a bit of green tape in the box in case someone couldn't tell by its location in the box that it was the ground wire.
Hope I didn't screw it up somehow. Everything works fine so far.
You need to fix this. By tying the grounded (a.k.a. "neutral") and grounding (a.k.a. "ground") conductor systems together at another point other than the main panel, as you've done at the subpanel, it allows return current which normally flows exclusively over the "neutral" conductors, to also flow over "ground" conductors, and anything tied to them. This can lead to voltage potential differences on supposedly safely grounded items, which can cause things like water pipes that give you a shock when you touch them, heating ducts that spark, etc.
There must be a way of installing two separate bus bars; if not, the panel could not be approved for use as a subpanel. Normally, the label states what, if any, additional parts are needed to turn it into a subpanel.
Often, you only need to remove a green screw or grounding strap to isolate the existing bus bar(s) from the chassis, so it/they can be used as the neutral bar(s). You then just get another bus bar and screw it directly to the sheet metal for use as the grounding bar.
In any event, even pulling all the neutrals and connecting them all together with a bunch of wirenuts and jumpers would be waaaay better than what you're doing now.
The big boxes sell ground bars of various sizes (number of holes) for Square D QO and Homeline panels for this very purpose. There is a threaded hole or pair of holes somewhere on the back of the panel box to receive this ground bar. If it's a QO panel, there is a long screw that grounds the neutral bar to the box; remove it. You're permitted to double-up the grounds, if the lugs are listed for it, but not the neutrals (if I remember correctly).
Be seeing you...
Thanks to all for replies.
I went back to where I bought the panel (HD) and sure enough, right there on the label it stated to buy the "Grounding Bus Kit" which they had on the shelf right above the panels. Of course, I think they should have included it, but then I wouldn't be able to buy a panel for 15 bucks!
Anyway, the nuetral bus IS isolated from the panel along with the hots. There are pre-drilled holes in about four different locations to install the grounding bus (also a Square D product). So, I guess this addresses the concern over using the manufacturer's preferred method.
Thanks for the input everyone!
Jim