Isolation of neutral at Sub Panels

[iwire]

Re: Isolation of neutral at Sub Panels

Originally posted by Ed MacLaren:
I'm sure awwt must have meant wired or unwired, not powered.

Well I hope so as I often check for continuity between neutral and ground live or dead.

The only difference will be a dead panel I get a "clean" tone on my meter on a live panel I get a tone with a 60 cycle warble.

This comes in handy say at a junction box with all black wires once you find the two conductors that are grounded you can identify the grounding conductor from the grounded conductor from the sound of the tone.

 

[hurk27]

Re: Isolation of neutral at Sub Panels

Eagle
I have never seen a no main panel with the neutral bar not isolated from the metal can? there are some main breaker panels that do have the neutral bar bolted to the can but the label on these say for service use only. these sometimes have a isolation kit that can be purchased, to allow for use as a sub-panel but they are rare.

The NEC is very specific about keeping the grounding wire and neutral separate after the first main means of disconnect. There is only one exception to this rule and that is only on an out building where there is no common metal paths between the two buildings. this includes phone lines and TV cable, water, gas that could become a parallel path for the neutral. Then and only then is it allowed to run a 3-wire feeder cable to the panel in the out building. but the neutral must be bonded to the grounding for this panel to provide a fault current path back to the transformer.

When you said that you "had no continuity between the grounding conductor and the neutral" was this because there was no grounding conductor ran back to the main panel? if this is the case then these panels are wired very dangerously and can shock someone if a short to ground were to occur. If there is only a ground rod running to this panel it will not fault a breaker if a short occurs and will cause a 120 volts on everything that is bonded to this panel. A ground-rod will not trip a breaker as the resistance is to high at 120 volts to cause enough current to flow. this is why there must be a grounding conductor ran with the feeder cable back to the main panel (where the grounding conductor and neutral are bonded together) this is to provide a path back to the source (transformer Via neutral) this is the only safe way to open the circuit breaker. There should always be continuity between the neutral and grounding as it is always tied together at the first means of disconnect.

So if you run across a panel that is only fed by a three conductor cable L1 L2 N then do not remove the ground/neutral bond until a grounding conductor has been ran back to the main service panel. As this would be much more dangerous than the neutral/ ground bond!

 

[dansan]

Re: Isolation of neutral at Sub Panels

408.20 does specifically say that grounding conductors and grounded conductors may not terminate on the same bar in a panelboard unless permitted or required by article 250

 

[karl riley]

Re: Isolation of neutral at Sub Panels

Take a simple question from a poster who wants to get a simple answer and twist it into needless complications and false statements (i.e., Bennie's). I am boiling.

Eagle, the answer is NO. In a subpanel the neutral bus is isolated from the panel. The equipment grounding bus is not bonded to the neutral bus.

In checking continuity on the panel before it is installed, you should have no continuity between neutral and ground busses. In checking the panel after it has been installed and wired, you will find continuity because both neutrals and EGCs go back to the main panel where they are connected. Hence you will see continuity, but it will not be from a connection at the subpanel.

I realize all these points were brought out in different posts, mixed in with the other stuff.
Why not give new posters straight answers and reserve the "in depth" discussions for the threads posted by the experienced enquirers? We are supposed to clarify rather than confuse.

OK. Now I can go to bed.

Karl

 

[Ed MacLaren]

Re: Isolation of neutral at Sub Panels

Eagle,
As others have stated, any connection between the grounded (neutral) conductor and the equipment enclosures, on the load side of the main disconnecting means, is not permitted.

I'm not sure if you were asking about the reason for this requirement.

The grounded (neutral) conductor carries the unbalanced load current in any multi-wire system.
An illegal bonding jumper permits the neutral to be in parallel with the equipment grounding conductor, which is not sized for continuous current.
It can be bare and is often an exposed conduit or cable armor. (Sketch below)

Ed

 

[bennie]

Re: Isolation of neutral at Sub Panels

Before anyone else loses any sleep, I will make an attempt to prove my statements.

If I added confusion to this thread, I am sorry. The confusion was already there according to the eagle.

A cable, or non-conductive raceway have different rules than a metal raceway supplied panel.408.20

The code requires that when the grounding method creates objectionable current, proper action is necessary to prevent it from occurring.

There is no words about separating the equipment ground conductors from the neutral conductors as being the only procedure, except when there is an equipment ground conductor with the supply conductors.408.20 for reference.

Interconnections between equipment ground conductors and the grounded circuit conductor(neutral) are "required" at the service panel. There is no section that forbids this at the other panels, when there is only 3 conducting paths to the source.

Like I have stated; show me the section that forbids interconnecting equipment ground conductors and the grounded neutral conductor at the panels when the grounding bar is identified for the purpose.408.20.

On Ed's schematic, remove the equipment ground conductor, and the parallel current is gone.

 

[iwire]

Re: Isolation of neutral at Sub Panels

Originally posted by eagle:
Can I get a simple explanation on the requirements and or need to isolate at the SUB.

I will try, a panel that is to be used as a "sub panel", (the code would call this panel "Load Side Equipment") must not have any continuity between the enclosure and the ground bar before any wires are connected to this panel.

Originally posted by eagle:
Question 1 : when testing for continuity at the sub .. I should find NO continuity between the branch circuit neutral and ground bar .. YES ... NO ?

There should be NO continuity between the branch circuit neutral and ground bar of a sub panel.

Until this panel is connected to the feeder, once you connect this panel to the feeder you will have continuity.

The voltage from your tester will flow from the ground bar at the sub panel down the equipment grounding conductor, back to the service panel and through the service panel common grounding / neutral connection and back up the neutral of the sub panel feeder to the neutral bar of the sub panel.

Originally posted by eagle:
Question 2 : If NO.. how is that avoided on sub panels that do not have the new type of stand off bars and they directly contact the panel frame ?

It can not be done with the panel you describe, that type of panel is for use as a service panel only, never to be used as a sub panel.

The two key codes about this, in my opinion are 224.5 which is the code article that prevents the use of the panel you describe with the neutral connected to the enclosure.

224.(5)Load-Side Grounding Connections. A grounding connection shall not be made to any grounded circuit conductor on the load side of the service disconnecting means except as otherwise permitted in this article.

And 250.142(B) Which prevents us from running a just 2 (or 3) hots and a neutral to a "sub panel" and using the neutral as the grounding means, as of course this "sub panel" enclosure and all the branch circuits from it must be grounded.

250.142 Use of Grounded Circuit Conductor for Grounding Equipment.

250.142(B) Load-Side Equipment.
Except as permitted in 250.30(A)(1) and 250.32(B), a grounded circuit conductor shall not be used for grounding non?current-carrying metal parts of equipment on the load side of the service disconnecting means or on the load side of a separately derived system disconnecting means or the overcurrent devices for a separately derived system not having a main disconnecting means.

One last thing, although many of us including myself often use the term "sub panel". that term is not in the code book at all.

This panel is treated the same as any other loads from a service panel it is in code terminology "Load Side Equipment".

Meaning the load side of the service panel or service disconnect, that has the Bonding Jumper (Neutral/Ground Jumper)

I hope this helps, I have tried to keep opinions out and code references in, it is a tough subject to give a yes or no answer to.

Bob

 

[iwire]

Re: Isolation of neutral at Sub Panels

Originally posted by bennie:
Like I have stated; show me the section that forbids interconnecting equipment ground conductors and the grounded neutral conductor at the panels when the grounding bar is identified for the purpose.408.20.

Bennie you have been shown the code articles that forbid this a number of times by many of us.

You just do not agree with everyone else, which is fine, you are more than entitled to your opinion.

But I also think you are doing a disservice to the members that are unsure of the code requirements of 250.

 

[bennie]

Re: Isolation of neutral at Sub Panels

I concede to everyone. I only wanted to make a very boring subject a little more interesting, and to point out there is other methods to accomplish the same end.

I am sorry if people are boiling over my remarks.

I suppose 2300 is enough anyway.

Thank you.

Bennie

 

[karl riley]

Re: Isolation of neutral at Sub Panels

Bennie, now that it is morning and I have had a good sleep (didn't dream about electricity) I re-read the posts and see that if Eagle read each one carefully and has stuck with the thread until now, he has had more than an education in not bonding the neutral in a subpanel. So maybe the way the thread developed was OK after all.

A story kept coming to me as I was waking up. A lady lends a pot to her neighbor. The neighbor returns it with a hole in it. The lady says, "Hey, there's a hole in my pot!". The neighbor replies:

"First, I never borrowed your pot.
Second, when I borrowed it there was a hole in it, and
third, when I returned it it was in perfect condition."

So when someone says NEC does not allow neutral/ground bonding in a subpanel you reply:

First, there is no such thing as a subpanel.
Second, it is permitted to bond neutral and ground in a subpanel.
Third, even if it is not permitted there is nothing wrong with it.

(Just trying to make a boring subject more interesting)

I am afraid I am super-sensitive about this subpanel ("load side equipment") topic simply because for the last 14 years I have been correcting these bonds in subpanels and have seen the problems they cause. It's a common error. I have also seen the confusion of electricians about it, and I always try to clear it up for them.

I am going to start a "25 ohm" thread soon. I hope you contribute your ideas to it.

Karl

 

[ryan_618]

Re: Isolation of neutral at Sub Panels

As an inspector I try very hard not to speculate future violations as I believe it is not my place to do so. One area that I will do this, however, is on this topic. When I inspect a residential interior panelboard I often see the bond screw in place, but not tightened down. I red-tag it even though it is not a violation yet. My reasoning is that if some homeowner that doesn't belong in the panelboard sees that screw, all they see is a "loose connection" and will probably tighten it. I feel justified in red-tagging this even though it is speculation.

 

[Guest]

Re: Isolation of neutral at Sub Panels

Karl:
Thanks for bringing this one full circle.

Bennie:
Please don't run off until you get to 10,000.

iWire (Bob):
Keep up the NEC cut/paste jobs. It helps a lot to see the codes.

Each wrong answer we get puts us one step closer to the right answer. I'll continue to try and hold up that portion of the equation

 

[eagle]

Re: Isolation of neutral at Sub Panels

Karl, Bennie, I wire

Thanks to all of you for the help. Jeez I didn't mean to start a S%%%storm with my question.

The reason for the question ... I am a new Combination Inspector. Yes I know I'm supposed to know everything .. at least according to some people. Combination inspectors are really generalists instead of say an ELectrical inspector that only does electric .. ALL OF THE TIME. IN addition,... many of the electrical inspectors started as electricians. They have a major head start on someone like me coming from 27 years as a Framing contractor.

Whew .. now that you have the picture ... and has been stated repeatedly .. there is tremendous confusion AT EVERY LEVEL on this topic by many inspectors, electricians and journeymen.

I thank all who contributed in setting me straight on this. In particular, Karl & IWIRE for reducing it down to what I was really looking for.

The question developed because I had been told in code class to check for isolation on the Neutral & Ground at subs. I understood that meant to look for the following on Rough Ins:

1. NO jumpers
2. No neutrals on ground bar and Vice/versa
3. No ground screws the neutral bar

I thought that since we seemed to be trying to do evrything we could to separate in every way I should not see continuity on the bars when HOT.

On rough ins I was further compounded and thought the above theory was correct because it did not show up at rough WITHOUT power. Every attempt at discussing this with more experienced electrical inspectors just led to more confusion and generic answers that did not fit.

Now I understand what to look for at SUBS.
Rough - NO continuity on the bars ..
Final - Continuity as these are bonded
at the main when it's hot

Each of you have helped this inspector and it is appreciated. This is what it's all about and this inspector welcomes help and knowledge from a tradesman any time their willing to give it.

Eagle

 

[bennie]

Re: Isolation of neutral at Sub Panels

Eagle: You didn't start a storm. I have to take the blame. I am discussing how things were in the past, and others are discussing the way things are now.

I believe in learning the dynamics of an application, not just memorizing the text of the rules.

The rules are as declared by the others, so ignore my opinions.

 

[iwire]

Re: Isolation of neutral at Sub Panels

Originally posted by bennie:
I believe in learning the dynamics of an application, not just memorizing the text of the rules.

Bennie I really want to know the "dynamics of an application" but that is not what I am paid for, nor will that info get me a final inspection.

Memorizing the text of the rules is exactly what I have to do to get the inspector to sign me off.

Even if I tell them I read it on the Internet.

 

[Ed MacLaren]

Re: Isolation of neutral at Sub Panels

There are 11 different forums (fora ??) now.

Perhaps there should be a another one where those of us who wish to bring forward controversial and "non-mainstream" subjects and ideas could do so. It could be called - Rants & Opinions

That could be a way of keeping this kind of discussion, which is often quite thought-provoking and valuable, from confusing the folks that just want a straight-forward NEC related answer.

Ed

[ October 11, 2003, 12:55 PM: Message edited by: Ed MacLaren ]

 

[bennie]

Re: Isolation of neutral at Sub Panels

Ed: I do know that my posts are creating a lot of controversy, and complaints to the moderators and the host. I may be asked to discontinue my participation in this forum.

When asked, of course I will stop. I will then start my own rants and complaint forum.

The forums that only answer a question with a number, have all failed from lack of interest. Some of the most recent posts are a week old.

This forum is the number one in participation and observers. I would like to think I have been a contributor to this happening.

If my absence is an improvement, then I am out of here as fast as I can click the mouse.

 

[Guest]

Re: Isolation of neutral at Sub Panels

Originally posted by eagle:
<snip>
Now I understand what to look for at SUBS.
Rough - NO continuity on the bars ..
Final - Continuity as these are bonded
at the main when it's hot<snip>

Hot or cold should not change the N-G continuity on the Final.

Whether it's rough or final should not be the deciding factor of if there is N-G continuity or not.

If the panels are made up the N-G continuity in the panels will be the same hot or cold, rough or final. The rule of thumb quoted above won't apply universally.

This is why it's important to understand the dynamics & the rules. I wish I could draw nice pictures. A picture would be worth a thousand words here.

../Wayne C.

[ October 11, 2003, 02:49 PM: Message edited by: awwt ]

 

[Guest]

Re: Isolation of neutral at Sub Panels

Originally posted by Ed MacLaren:
<snip>It could be called - Rants & Opinions <snip>

It would be valuable to have a forum section where it's OK to have a discussion that is not confined to ending up with a citation from the NEC.

Additionally, I personally would like to see a forum section called "Workmanship & Tips" (or such) where we could share ideas for taking installations beyond code minimum.

../Wayne C.

[ October 11, 2003, 03:02 PM: Message edited by: awwt ]

 

[karl riley]

Re: Isolation of neutral at Sub Panels

Ed, I think you are right on.

Eagle, AWWT is right that if the subpanel is wired there will be continuity (since it is connected to the service panel, hot or cold.

One detail: With a new panel it is not hard to visually check for a bonding screw or other intentional bonds of neutral to box, as well as EGCs and neutrals on the same bus. If you check for continuity when hot it is better if there are no loads on. Any load will put voltage on the neutral (usually under 1 V) relative to ground. The continuity tester has its own DC battery and is designed to be used on dead circuits.

When checking for continuity in a subpanel in a functioning facility with normal loads on, particularly when the panel is jammed full with spaghetti and it is difficult to see a sneaky bond wire or screw, I use the voltage function of the meter.

If there is a N/G bond you will see very low millivolts. If the neutral bus is isolated you will see over 100 mV usually, going up to close to 1V sometimes. Of course this depends on there being a load on the feed neutral, which is usually the case.

Karl