I purchased a Cutler Hammer 70am load center and would like to use it as a sub panel. It only has a bus bar for the neutral, and not one for the ground.
In the past i have seen where someone has placed the grounds and the neutrals together on that single neutral bus bar. Somewhere along the way I read that you are not supposed to do this. They recommended mounting a separate bus bar for the ground. It would not “float” like the neutral bus bar, but actually be a metal to metal “bonded” attachment.
What say you guys?
Replies
You have it right.
If it's a subpanel you must buy the separate ground bar and keep grounds and neutrals separate. If it's a main panel you generally (with some exceptions) don't need to do this (which is why the panel is delivered without the separate ground bar).
Note that you should remove the factory-installed jumper between ground and the neutral bar.
Are you sure that bus bar is not grounded?
I'll bet it is.
In order for it to be grounded, that bus bar would have to be connected to a ground wire that runs to a grounding rod that is in the ground-or something along those lines.The neutral bus bar is "floating", attached to the box, but there is plastic between the box and the bar. A screw is included, separately, in case you want to bond the bar to the box. Why someone would want to do that, I would like to know.
The neutral bus bar is "floating", attached to the box, but there is plastic between the box and the bar. A screw is included, separately, in case you want to bond the bar to the box. Why someone would want to do that, I would like to know.
.They would want to do that if the box is being used as your primary service panel.
If the panel is a "main", and if there is no separate disconnect enclosure or some such where bonding occurs, the neutral and ground are bonded together in the panel.
As I stood before the gates I realized that I never want to be as certain about anything as were the people who built this place. --Rabbi Sheila Peltz, on her visit to Auschwitz
>> A screw is included, separately, in case you want to bond the bar to the box. Why someone would want to do that, I would like to know.<<
This is required and SOP, if you were to use this particular panel as a service entrance panel.
3 wire drop from the POCO, 2 hots and a neutral.
1 ground wire from driven ground rod / UFER / etc.
POCO neutral and ground wire from rods BOTH are attached to the neutral bar in the panel.
The neutral bar is then bonded to the panel enclosure via the screw provided to
provide a ground path for the metal panel enclosure.
If there was a fault inside the panel, and there was not a ground path present, you become the conductor to ground as soon as you touch the outside of the panel. Generally not desirable.......
In the case of a sub-panel, a ground path is provided via the ground wire back to your main SEP.
Jim Never underestimate the value of a sharp pencil or good light.
Glad to see this question raised as I am just in the process of getting electricity out to my pole shed and have a few questions. My shed is located about 200 ft from the house. Based on feedback from the local electrical supply shop I ran Stevens 2-2-4 aluminum wire to it. I am putting a 100 amp box in the shed.
First question: Since the wire I ran out there does not have a ground in it do I have to attach a ground rod and cable to the ground bar in the box? If so, how long of a ground rod do I need to drive into the ground and since this is a dirt floor do I do it outside of the building or inside?
2nd question: When I hook up to the main service panel what is the largest breaker I can hook up? I'm guessing since it's a 100 amp box, that's my max? Or is that overkill and should I go with something like a 60 amp breaker? I will just be running my table saw and equipment like that in the building.
Thanks in advance for any help!
This is somewhat sticky, I would have run 4 - THWN single conductors in underground conduit to feed this building. 2 hots, neutral and insulated ground.
Seeing as how you already have a wire run in place --- I am not positive of the answer to your question -- also do not know for sure if this should be treated as a service entrance or as a sub-panel in terms of wiring within the panel.
Will shout out to BillHartmann about your questions, resident NEC consultant, if he has not posted already........
>>Since the wire I ran out there does not have a ground in it do I have to attach a ground rod and cable to the ground bar in the box?<<
Ground rods - General info:
2 rods; 8'x5/8"; copper or copper clad; driven outside of the building; minimum separation is 10' between the rods; continous run of bare #4 or #6 copper, box to rod to rod; secured with direct burial cable clamps. Both wire and rod tops should be trenched in to provide 6" cover for the rod tops and wire.
>>what is the largest breaker I can hook up?<< 100A, but I would use a 60 due to voltage drop over the 200' run -- 60A should be fine for your intended use and is less than the 100 amp maximum rating of the box.
>>Thanks in advance for any help!<<
Working on it!
JimNever underestimate the value of a sharp pencil or good light.
The rules for outbuildings changed about two years ago, so you need to be sure you get the correct advice, and you may also want to check with your inspector to see what rules they're enforcing.IIRC, the new rules treat an outbuilding with its own panel pretty much like a main service entrance -- you have a grounding "system" in the building (2-3 different rods, concrete-encased electrodes, or whatever) and bond the ground and neutral in the panel. Under the old rules, IIRC, you carried ground and neutral from the supplying building, did not bond in the new panel, but did have a ground system. (But my memory isn't all that reliable on such topics, so get an authoritative answer.)
As I stood before the gates I realized that I never want to be as certain about anything as were the people who built this place. --Rabbi Sheila Peltz, on her visit to Auschwitz
You have that backwards.Old is 3 wire with bonded panel, if no other metalic paths.Now it is always 4 wire with isolated neutral.In either case a ground electrode systme is needed.
.
William the Geezer, the sequel to Billy the Kid - Shoe
A slight digression.The purpose of a ground electrode system (grounds rods and the like) are completely different from the equipment grounding conductor (the green/bare wire and ground pin on receptacles).The purpose of the ground electrode system is to dissipate any surges or lightning on the supply lines.EACH SEPARATE STRUCTURE needs a ground electrode system no matter if the feed has a ground wire or not.The equipment grounding conductor and related bonding and connection to equipment is to make sure that anything metallic that you might come in contact with is at the same potential. It also provides a path for fault currents. And if you any "normal current" flowing through the ground wire you will have a voltage drop and thus it is at a different potential.So the neutral is bonded to the ground electrode system and equipment grounding conductor at one place and only one place in a structure. At that is that the service entrance, which is usually the main panel.Any other panels in that structure is a sub-panel and the neutral needs to be isolated from equipment grounding conductor.Up to the 2008 NEC out building that did not have any other metallic paths (water pipes, phone/cable wires are the most common) could be treated as if the panel in the outbuilding was a service entrance and thus feed it with 3 wires and the neutral bonded to the ground electrode system and ground bus.That option was removed from the NEC and under the current version it can only be feed by a 4 wire feeder and the panel treated as a sub-panel.However, I don't have any idea of what version of the NEC that you community has adopted, if any. Nor any local amendments that might affect this.Without going into all of the options the most common ground electrode system is two ground rods. They have to be 8 ft long and at least 6 ft separation..
William the Geezer, the sequel to Billy the Kid - Shoe
Bill,
Thanks for the great explanation. Regarding NEC code and regulations, I can't say with any certainty that I'll ever have this inspected so I'm not so concerned about passing inspection. My concern would now be that since I have ran a 3 part wire to the structure, would I have a safety issue if I wired it prior to the 2008 standards? Sounds like the previous version of the code says I'd need to just bond the ground and the neutral and then place grounding rods. Is there a specific reason this was changed?? I don't want to do something wrong yet I don't want to dig up my wire and lay a new one.
Thanks again for the great explanation.
I don't know why it was changed. The only reason that I can think of is that it was argued that a metal pipe or cable might be run in the future.I don't see any big safety problem..
William the Geezer, the sequel to Billy the Kid - Shoe
A commercial sparky that helped me with my distant shop wiring project (as did you, thanks again) about a year or so ago. We talked about the 4 wire requirement. He seemed incredulous, but he told me that they were concerned about the differences in ground potential from widely separated grounds - basically creating a low level current path. That was probably the local inspector's take on it, but nonetheless, that's what they told a group of electricians in the Seattle area back when they committed to the latest NEC. I can't imagine how much difference in ground potential you might find in the 50 - 300' range (i.e. a typical distance for residential subpanels), but it would be interesting to know if anyone has heard of a case where it's enough to say, trip an AFCI? More of a Mike Holt type question, but I'm not allowed to ask stuff over there!-t
As you presented it that is not a possibility unless you have 50 long arms and reach both points at the same time.Now ground differences can cause real problems. Buy to have those you have to current flowing through the ground electrodes. And current is not suppose to be flowing in the ground electrodes.This is often caused by a neutral connection problem. Most often at the house. But one person here had a problem where they where getting shocked when in the crawlspace between the earth and copper piping.Turns out that the neutral connection on the primary to the POCO transformer was bad and the neutral currents where being returned via the homes neutral and ground rods..
William the Geezer, the sequel to Billy the Kid - Shoe
I see by your profile you're in Minnesota, so for the record the 2008 edition of the NEC applies.
Man, I went to two electric supply houses when looking for what cable to use and they both told me the Stevens 224. I wish they had given me the correct info so I don't have this moral dilemma now.
I hear clerks in supply houses { and Home Depot & Lowes} being questioned on the proper way to do something or what materials are best etc. Everyone should remember that those folks are SALES CLERKS not real tradesmen. Sometimes the information you receive from such sources is worth just exactly what you paid for it.Sorry to hear of your situation. I concur with others that you will be safe if you treat it as a separate new service. Bond the neutral to the new ground rods and go with it.Chuck
Well here we go again - another 3-wire vs. 4-wire discussion.
And this one is definitely NOT for existing premise wiring.
Maybe we need to wait for Reno to weigh in on this!
Jim x 3
I think you should be able to buy a second bus bar as an accessory so you can use it as a sub panel - check with the store where you bought it.
>>....Somewhere along the way I read that you are not supposed to do this. They recommended mounting a separate bus bar for the ground. It would not "float" like the neutral bus bar, but actually be a metal to metal "bonded" attachment.<<
Your reading was correct, memory not bad also.
You need to buy a separate "accessory" ground buss bar made by CH -- screws will be in the baggie with the bar -- the same dealer as the panel will carry them - various lengths / number of connection holes, get the one listed for your panel.
For use as a sub-panel: Check to be sure the factory installed neutral bar is not bonded to the panel enclosure (usually a green screw or bracket). If it is bonded, remove the screw / bracket and discard. (Or save it in some coffee can where you will never find it -- my trick)
Install new ground bar using factory threaded holes in panel enclosure.
Get out your continuity meter:
There should be continuity between your new ground bar and the panel enclosure.
There should not be continuity between the neutral bar and the panel enclosure (or the new ground bar).
If above conditions are not met -- determine why not and remedy the situation.
Assuming your new sub-panel is in the same building as the main panel: Feed sub-panel with Xawg-3 w/ ground cable or equivalent wire in conduit. No additional ground rods are required.
Black + Red = hot lugs or main breaker; white = neutral bar; bare or green = ground bar.
Neutral wires to the circuits fed by this panel go to the neutal bar; grounds to the ground bar.
Jim