Isolating netral bus from ground bus

I was looking at my sub panel beside my main panel. (It is about 2 feet away and was added a few years ago because of lack of space in
main panel).
I believe I read that the netral and ground busses must be isolated on a sub panel. When I checked with a continity tester, it beeped meaning they are connected. This is a Square D Homeline series model number HOMC2OU100C with a main breaker.
It looks like the bonding screw was removed though? There are two blue screws one at the neutral lug area and one at the ground lug area. I removed one and still contnuity. I removed both and no continuity. These look like the screws you remove to remove the interrior of the cabinet.
SHould I leave the screws out? Can anyone help me with this model?
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stryped wrote:

Are the ground and neutral wires connected to the panel? If they are, then ground and neutral will be tied together at the main panel so they will measure continuity in the subpanel as well. They should not be locally bonded in the subpanel though.
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stryped wrote:

I wouldn't be removing any bonding screws in a live panel!
--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"
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Put all screws back where you found them. You're getting continuity between the neutral and ground because the two are bonded together in the main panel.
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I removed the power wire's and ground from the main panel to the sub panel before doing the continuity test. This means I should not have had continuity right? I cant understand why it is showing continuity then.
How will an inspector check for this by the way?
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By the way, the neutral is on the left of the enclosure and the ground is on the right. These both run vertically. There is a bar running horizontally between the two. It looks like in the center of this bar is where the green bonding screw goes and it is not there. Does this horizontal bar also somehow have to be removed to isolate the two?
As I said the 4-3 power wire is gone. I do have two circuits connected to an upstair heat pump/air conditioner but power to the panel is off.
I am just kind of perplexed. It has to be something simple.
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That jumper bar should not be there and the ground bar should be bonded to the panel box.
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.
Can you tell me how to remove that bar if it is needed? I am not so sure it is removeable?
This is a similar enclosure: http://static.schneider-electric.us/docs/Electrical%20Distribution/Load%20Centers/QO%20Three%20Phase%20Load%20Centers/40281-365-01.pdf I think page 3 talks about bonding.
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Everything is removable, one way or another! If the ends are screwed down simply remove the screws and the jumper will come off. If there are no screws and both bars and the jumper are one piece then cut a 1" section out of the jumper.
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Am I really suppsed to remove that thing?
Here is a copy of the directions. It talks about bonding on page 3: http://static.schneider-electric.us/docs/Electrical%20Distribution/Load%20Centers/QO%20Three%20Phase%20Load%20Centers/40281-365-01.pdf
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wrote:

http://static.schneider-electric.us/docs/Electrical%20Distribution/Load%20Centers/QO%20Three%20Phase%20Load%20Centers/40281-365-01.pdf
What aren't you understanding? In the subpanel the neutral and ground do not get connected together. The ground gets connected (bonded) to the breaker panel box. You do whatever you have to do to make this happen.
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I think I have figured out what is wrong.
I dont think the square d panel I am refering to in the attached garage came with a grounding bus. (The GE panel int he attached garage did). What I was thinking was the grounding bus is actually I believe a second neutral bus.
I will check for continuity between the two busses in the cabinet and the enclosure and if there is none, will buy one or two grounding buses. I think that might be the problem all along.
What I dont understand is why the need to separate the neutral bus and ground as they all end up combined in the main panel anyway.
Also, I always heard it was bad to have multiple ground paths. If I have a ground rod for the house and one for the detached garage, arent these all connected? All sub panels will be attached to the house ground and the sub panel in the detached garage will also be attached to another ground rod. AM I misisng something?
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The problem people are usually talking about with multiple grounding paths is in electronic circuits were it can introduce loop currents that cause noise in audio and digital circuits that interfere with normal function. In power wiring, as done in North America, the whole system is based on what is called Multi Grounded Neutral or MGN. Next time you are out for a walk look at the utility poles you pass and you will see that many of them have a Ground Rod and a Grounding Electrode Conductor running down the pole from any transformers, switch gear, lightning arresters, and so forth. The reason that each piece of equipment or building gets it's own grounding is that lightning has such a fast voltage rise that it acts like a very high frequency current. If it does not have a ready path to earth it will equalize to other conductive objects destructively by vaporizing any non- conductive material in it's way. -- Tom Horne
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stryped wrote:

If they are bonded together in a sub-panel and the neutral feeding the sub-panel opens, then neutral current will be flowing in the grounding wire between sub-panel and main panel. Even with both conductors connected correctly, the neutral current will still split between these two parallel paths on it's return to the main panel.
Deliberate current flow in any grounding conductor is bad because the current can cause a voltage rise on the grounding conductor and that's a bad thing.

'multiple ground paths' can be a bad thing in signaling systems (telephone, instrumentation, cableTV, network, etc...). They can form a 'ground loop' that will cause a problem with noise/interference with the signals.
That's not the same thing as providing multiple grounding rods for the main service entrance.
daestrom
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stryped wrote:

That is probably right. Panels typically don't come with a ground bar. They aren't needed for a service panel - since the ground and neutral are bonded, the same bar can be used for both the neutrals and grounds. A ground bar is needed for a subpanel. The label for the panel should give you the part number for the correct ground bar. Earthing electrode(s) attach to the ground bar.

--
bud--

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Don't you have that backwards? Panels often don't come with a NEUTRAL bar but the ground bar is required because grounds everywhere are bonded to the case and in an entrance the neutrals get tied to the grounds. It's the additional neutral bar that's need for a sub-panel.
<snip>
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If you're trying to impress us by appearing to be intelligent and knowing what you're talking about, then I can honestly say you've failed miserably.
Panels come with a neutral bar. If the panel is the main one then both neutrals and grounds get tied to it. If the panel is to be a subpanel then the neutrals get tied to the bar that comes with the panel and a separate add-on bar is installed for the grounds.
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wrote:

Trying to look impressive? You too failed, needle dick.

A neutral bar isn't bonded to the case. A ground bar is.

In the boxes I've installed (not many admittedly) you add the neutral bar if it's a sub panel. The bar that's in there is bonded to the case, which a neutral bar wouldn't be.
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krw wrote:

In US services the neutral is bonded to "ground". That (almost always) occurs in the service circuit breaker panel. A service neutral bar is also a ground bar.

Almost all US services come with a neutral. (The ones that don't that I can think of are corner grounded delta and ungrounded delta - both are unusual.) Because neutrals are part of the utility supply, I don't remember any panel (particularly SquareD) I have installed that did not come with a neutral bar, because it is (almost always) needed.
Since in a service the neutral and ground are bonded, the neutral bar can also be used as the ground bar - a separate ground bar is not required. I don't remember many panels that come with a ground bar. For subpanels a ground bar is usually (not always) required, and is available from the manufacturer. (If a subpanel was wired with all EMT there may not be any ground wires and no ground bar is required.)
As of the 2008NEC you explicitly can not connect a neutral to a ground bar.
--
bud--

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wrote:

Right?
I am confused. The supplied bar isn't bonded to the case? The Square-D I bought a few months ago (for a sub) had a ground bar across the bottom. I added neutral bars along the sides. Perhaps it's like accountants with their "credits" and "debits"? ;-)

Then why is it called a neutral bar if it can be either used as a ground bar or a neutral bar, and the added bars are used as neutral bars?

Ok, there is obviously something in the definition I'm missing.
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