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Old 02-19-2008, 09:36 PM   #16
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Can I add a second grounding bar to a GE box?


Lets take a look at this a little closer with a diagram. An appliance that requires grounding is plugged into the outlet. BTW I'm not trying to say anybody is wrong or set a trap here or play know it all. I think Speedy has correctly stated that this is a widely misunderstood concept. This is a question well worth exploring for the benefit of DIYers.
First this probably isn't a likely possibilty but it is those unlikely things that get you. Think about this in terms of the appliance switch closed or open, complete circuit or not, When will current flow and when will it not.
1.) Which situation creates the biggest danger and why?
2.) Are both situations correctly shown as far as how neutral current will flow?
3.) Is the white wire (gray in diagram) a current carrying wire or just a ground wire like the green?
4.) If the appliance can be energized... is it energized with voltage, current or is it both or neither one?
So if any of you DIYers want to take a stab at these questions have at it. I'm sure the electricians here will chime in to help explain whether your wrong or right.
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Last edited by Stubbie; 02-20-2008 at 11:29 AM.
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Old 02-20-2008, 05:49 AM   #17
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Can I add a second grounding bar to a GE box?


Thank you Stubbie!
This is a perfect example of what I meant. You have to think of where the wires are going, NOT where the came from.
In other words, you need to (even though I hate this cliche) think outside the box. Panel box that is.

Look at Situation B above. Sure, someone will say "Just make sure the screw is tight."
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Answers based on the 2008 & 2011 NEC.
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Old 02-20-2008, 08:36 AM   #18
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Can I add a second grounding bar to a GE box?


Is it therefore a better practice to when wiring a MAIN panel that there be two separate bars, one for the ground and one for the neutral and have them then bound through the panel casing via the green grounding screw? This would totally avoid this problem.

Last edited by Randell Tarin; 02-20-2008 at 08:48 AM.
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Old 02-20-2008, 08:49 AM   #19
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Can I add a second grounding bar to a GE box?


Quote:
Originally Posted by Randell Tarin View Post
Is it therefore a better practice to when wiring a MAIN panel that there be two separate bars, one for the ground and one for the neutral and have them then bound through the panel casing via the green grounding screw? This would totally avoid this problem.

I would also like to know the answer to this...

is there any difference to having all the neutrals on 1 bar and all the grounds on another in a main panel where they ARE bonded?
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Old 02-20-2008, 09:10 AM   #20
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Can I add a second grounding bar to a GE box?


I have a question regarding 480.40 Exception: Equiptment grounding conductors shall not be connected to a terminal bar provided for grounded conductors unless the bar is identified for the purpose and is located where interconnection between equiptment grounding conductors and grounded curcuit conductors is permitted or required by article 250.



So, basiclly it is saying that it is okay for neutrals (grounded) and grounds (grounding) to terminate on the same bar provided that particular bar is identified for the purpose, right? So, how do you tell if it is?


Also, a question about 480.41 Grounded Coductor Terminations. Each grounded conductor shall terminate within the panelboard in an individual terminal that is not also used for another conductor.

Exception: Grounded conductors of circuits with parallel conductors shall be permitted to terminate if the terminal for connection of more than one conductor.

What does that mean with regards to parallel conductors?
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Old 02-20-2008, 11:30 AM   #21
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Can I add a second grounding bar to a GE box?


Quote:
Originally Posted by Randell Tarin View Post
Is it therefore a better practice to when wiring a MAIN panel that there be two separate bars, one for the ground and one for the neutral and have them then bound through the panel casing via the green grounding screw? This would totally avoid this problem.

Yes, better practice. That however doesn't make it necessarily bad to land a neutral on one screw and a ground on another of the same bar, so long as it isn't the SAME screw.

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Old 02-20-2008, 11:35 AM   #22
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Can I add a second grounding bar to a GE box?


Well it looks like we are on our way to a long thread....hopefully not as long as the you know what thread.....

I added a few items to the diagram ... that being the insulators of the neutral bar, the main bonding jumper or screw and the note at the bottom.

This is going to take a while to dissect what is going on in the diagram and I don't want to do it in one long 3 page post. So we will take it in situations first that being situation A then situation B.

There is one more situation... that being the neutral of a branch circuit in one hole by itself and equipment ground of that same branch circuit in another hole of the neutral bar. This situation I think we can all agree is the code compliant one so lets leave it at that.

As an added note 'neutral' as it relates to line to neutral loads of a 120 volt circuit is not entirely accurate. The white wire in 120 volt branch circuits that are not multiwires are merely grounded legs but lets not let that muddy the waters. A true neutral in simplest terms, such as the Service Neutral, carries the unbalanced load of more than one ungrounded conductor.

I can't sit here all day and discuss this (I do have a life) so lets start to discuss Situation A first.

Some understanding of the behavior of current flow in single phase systems for residences might be useful. Lets let it suffice to say current seeks its source and it will take all paths to get there. The SOURCE is the transformer.. be it a pad mount or on a pole. The two primary paths to get there are the ungrounded conductors of the service drop or lateral and the service neutral. The only other path would be through the dirt to the ground rod of the transformer then up to the center tap where the service neutral (grounded conductor) connects. Also remember that alternating (AC) current reverses direction with relation to its frequency.. in the USA that is 60 Hz or 60 cycles per second.

I'll be back in a while and we can get started with situation A. I'm retired.... remember... and the wife has long lists for us retired husbands. I told her that I do the housework what more do you want? Her reply was that more than once a month would be nice.....

All comments and input from others is a plus, will save me some typing....

Last edited by Stubbie; 02-20-2008 at 12:11 PM.
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Old 02-20-2008, 02:04 PM   #23
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Can I add a second grounding bar to a GE box?


Crack that whip Mrs. Stubbie!
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Old 02-20-2008, 05:01 PM   #24
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Can I add a second grounding bar to a GE box?


Printing off the image may help in referencing it.


Situation A

This situation where a neutral was placed under the same screw with an equipment ground was common practice by many electricians and was approved by inspectors and I wouldn't be to surprised if it still is being done.
The NEC specifically prohibits the practice but I'm not sure what code cycle that occurred in.

With the appliance switch opened there is 120 volts at the switch, nothing happens of course till we close that switch. When we close that switch our appliance operates and we are solidly connected thru a load resistance or impedance to the neutral bar in the panel which is bonded to the service neutral. That connection is via the neutral wire of the branch circuit. This completed circuit connects us to the center tap of the transformer which is at 0 volts. So the completion of that circuit by closing the switch connects us from a potential of 120 volts to 0 volts. By definition current must flow in a single phase AC system by our standards. The current will take all paths based on total resistance and/or impedances to get to that center tap of the transformer. The lower the resistance or impedance the more current that will take that path versus the paths with higher resistances or impedances. In ac circuits we are primarily concerned with impedance. Impedance being imposed by components /devices on the circuit. On the neutral side of the branch circuit their are very few impedances unless we impose them on the circuit. Once current travels thru the load their is no impedance on the neutral wire only the resistance of the copper and voltage drop is virtually gone since we are just traveling a copper wire back to the neutral bar. As a result there is virtually no voltage on the neutral just current flow which changes direction 120 times per second.

Looking at the diagram since the most current takes the lowest path of impedance back to the source , that path would obviously be up the neutral bar out the service neutral and on to the transformer. If we were to run parallel service neutrals of the same size and same resistance and connect them to the neutral bar the total current would split equally on both neutrals. So if I had 20 amps returning on the neutral bar 10 amps would travel on one of the service neutrals and 10 amps on the other.

Now we have a equipment ground connected to that neutral because it is under the same screw. So the resistance/impedance of that equipment ground is only the copper in the wire....pretty darn low resistance. Problem is it runs back to the receptacle and to the equipment ground in the cord of the plugged in appliance up the cord egc to the metal frame of the appliance and stops there. There is no completed path back to the source. Neutral current will not take that path it wants to get to that center tap. Unless we impose a path of near zero resistance from the metal case of that appliance back to the source, essentially creating a parallel path to the center tap of the transformer. If we impose a high resistance path at the appliance with a much lower impedance path available back at the bonded neutral bar we likely will not even get a tingle IMO. This is why we can touch the metal of the main breaker panel even though it is bonded to the current carrying neutral. The key here is as long as that screw stays tight it is no different than having neutral in its separate hole and ground in its separate hole. This will change with situation B.

It is important to note that fault current will take the path of the equipment ground but it originates by convention at the origin of the fault and travels the egc to the neutral bar and out to the transformer center tap not vice versa. Since I love diagrams here is one to show this concept.
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Last edited by Stubbie; 02-21-2008 at 10:13 AM.
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Old 02-20-2008, 10:00 PM   #25
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Can I add a second grounding bar to a GE box?


Quote:
So, basiclly it is saying that it is okay for neutrals (grounded) and grounds (grounding) to terminate on the same bar provided that particular bar is identified for the purpose, right? So, how do you tell if it is?
In a main panel (housing the main breaker disconnect) neutrals and grounds are bonded to the service grounded conductor (Neutral) and a main bonding jumper is installed from the neutral bar into the metal of the can. So if the panel is a main panel used as the service equipment the bar(s) that the service grounded connductor is bonded with can accept both neutrals and grounds from the branch circuts and and feeders. These bars are always on insulating stand offs from the metal of the can. So simply put any neutral bar can have both neutrals and grounds landed on it if it is in the panel being used as the service equipment. The exception being a added ground bar that fastens directly to the metal of the panel and is not on insulators you can only connect grounds. There is one exception with panels that are in detached buildings with no other metallic paths beside the feeder between them. This is no longer allowed in the 2008 NEC but until your authority adopts it would still be legal but is not recommended.


Quote:
Also, a question about 480.41 Grounded Coductor Terminations. Each grounded conductor shall terminate within the panelboard in an individual terminal that is not also used for another conductor.

Exception: Grounded conductors of circuits with parallel conductors shall be permitted to terminate if the terminal for connection of more than one conductor.

What does that mean with regards to parallel conductors?
It simply means that for parallel sevice entrance neutrals like in a 320 amp meter base for 400 amp services may connect to one lug if it is rated for 2 wires.

Last edited by Stubbie; 02-20-2008 at 10:02 PM.
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Old 02-20-2008, 10:19 PM   #26
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Can I add a second grounding bar to a GE box?


While we await my long desertation on Situation B anyone of you DIYers care to offer why they do not want two neutrals under the same screw on the neutral bar?
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Old 02-20-2008, 11:21 PM   #27
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Can I add a second grounding bar to a GE box?


In rereading my use of resistance vs impedance I may have entered some confusion that should be clarified. When I speak of resistance in an alternating current I'm talking about the resistance of current flow with respect to the material of the wire. If I run a wire into the dirt much like you do on a gec to a ground rod you have very low resistance in that copper wire but relatively high impedance to the flow of current getting back to the source because it ends in dirt and does not maintain that low resistance back to the transformer.
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Old 02-20-2008, 11:24 PM   #28
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Can I add a second grounding bar to a GE box?


Assuming the wires continue to touch each other but not the neutral bar, and if the neutrals are on different legs, the loads on those circuits will see 240 V? I really ought to try drawing a picture but intuitively this seems right. If the neutrals are on the same leg, then the loads simply won't work.
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Old 02-20-2008, 11:35 PM   #29
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Can I add a second grounding bar to a GE box?


Quote:
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While we await my long desertation on Situation B anyone of you DIYers care to offer why they do not want two neutrals under the same screw on the neutral bar?

I will explain real easy.,,

what happend when i unscrew this the current of netural will stop feeding at the netual lug it will find current on other netural wire and can do funny thing along the way.

now pay attetion to this one .,, if you have multiwire branch circuit this will get pretty crazy anytime you remove the netural on MWBC anything still on either circuit will smoked the voltage will go up or down depending on connection and load.

Now you understand why we never put two netrual wire in each netualbus bar holes.

Merci, Marc
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Old 02-20-2008, 11:42 PM   #30
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Can I add a second grounding bar to a GE box?


Hi Frency

It's friggin 12 degrees down here in Kansas, the dog doesn't even want to go outside.

Are you able to see the eclipse of the moon up in the big W state. All clouds here so can't see a thing...

Oh.... and you get a A+ on your answer.

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