First Question: Neutral on Sub Panel

[Acorn Home]

First of all, great site. Lots of good questions/answers here.

I just finished taking the course by AHIT. It was good, but have some unanswered questions. Here is the one I am particularly confused about:

"The neutral wire must be isolated for the sub-panel (Wire cannot come into contact with the panel)" - WHY?

If it's allowed in the main panel, why not in the sub-panel? I have seen lots of electrician 'bond' the neutral bus to the sub-panel via a strap. Are they all wrong?

TIA

[Jerry Peck]

Hey Acorn, please click on the 'Contact Us' at the bottom of the page and ask Brian to reset your user name to your real name.

That's what we use here, as you have seen on the other posts, helps get to know each other.

Thanks.

[Jim Luttrall]

Hey Acorn, welcome aboard.
Try using the search feature for past threads on this subject for more information, lots more information to be found.
In general the ground is only supposed to be bonded to the neutral at the service equipment. There should not be current on the ground wires as a general practice, only in a ground fault type situation. If you connect the neutral and ground together at multiple points in the service, then the ground becomes a conductor, a bad thing.

[Acorn Home]

Thanks guys. I just updated my signature with my name / company that I just registered. Webiste is coming soon...

[Gunnar Alquist]

If it's allowed in the main panel, why not in the sub-panel? I have seen lots of electrician 'bond' the neutral bus to the sub-panel via a strap. Are they all wrong?TIA

It is not "allowed" at the service equipment (main panel), it is required. While that is likely what you meant, there is a difference.

Yes, if the neutral terminal is bonded to any panel other than the service equipment, then it is indeed wrong and should be corrected. Yes, you will see it regularly and you should report it.

The neutral wire does not carry voltage, but it does carry current (amperage). If the neutral and ground are bonded together, then the ground could be carrying some of the current. But, the ground is there only as a safety/backup and is not supposed to carry current, except in rare cases where there is a fault. Therefore, neutral and ground are isolated everywhere, except in the service equipment.

[Jerry Peck]

have some unanswered questions. Here is the one I am particularly confused about:

"The neutral wire must be isolated for the sub-panel (Wire cannot come into contact with the panel)" - WHY?

If it's allowed in the main panel, why not in the sub-panel? I have seen lots of electrician 'bond' the neutral bus to the sub-panel via a strap. Are they all wrong?

Welcome to THE inspectors forum.

First, let's stop using the terms "main panel" and "sub-panel" as those are all wired the same anyway.

Use "service equipment" and "not service equipment" (i.e, "not service equipment" is just a plain old "panel").

As Gunnar said, the neutral is *REQUIRED* to be bonded to ground at the "service equipment". This is also where the system ground is connected (i.e., the grounding electrode system). The "service equipment" is the common point in the electrical system.

The neutral *IS NOT ALLOWED* to be bonded to ground at any location downstream from the "service equipment".

A simple explanation is:

If the neutral becomes (or is intentionally) bonded to ground downstream of the service equipment, the neutral current now has multiple paths back to the service equipment.

Equipment grounding conductors ("grounds" or "grounding conductors") are designed and installed such that their intent is to not carry any intended current. They only carry unintended ground fault current.

Let's say you have a metal raceway serving as the grounding conductor and you have neutral current on it. None of the fittings are designed or intended to carry that current, thus there will be excessive resistance, overheating, which not only leads to various things happening, but, when you disconnect the metal raceway to make a repair, you may likely get a large arc, resulting in high voltage on one side, with you standing there holding both sides, you now become the neutral path with that voltage as the driving force across you. Best case scenario is that you only get a shock, worst case scenario is that you get electrocuted and never make it back here to tell us about it. :(

[Acorn Home]

Thanks for the replies guys.

If the neutral bus and ground bus are mounted to the panel via screws, doesn't that mean they are bonded?

Sorry for the newbie questions, but electrical was never my strong point :)

[Jerry Peck]

If the neutral bus and ground bus are mounted to the panel via screws, doesn't that mean they are bonded?

Typically, the neutral and ground bars on mounted on plastic insulator standoffs.

The exception being those ground bars which are mounted directly to the back of the enclosure with screws.

Neutral bars are never mounted that way ... unless the enclosure is "Suitable for Service Equipment ONLY". In which case it is not allowed to be used for anything other than service equipment.

[Acorn Home]

Thanks for the replies guys. Basically, I did not know that the neutral bus is mounted on insulators.

Anyway, here is a good site with more related info....

Mounting And Wiring A New Sub-Panel - Old House Electrical Update (http://www.hammerzone.com/archives/elect/panel/sub_panel/01/new.htm)

[Corn Walker]

Ah... a subsidiary panel. That would explain the "sub" in sub-panel. And here Jerry thought they were panels salvaged from submarines and sold at a discount in bog box stores.

What the site doesn't mention and should (seeing as its level of detail and tone appear to orient it to the DIY homeowner) is that the neutral conductors should not be so long as touch the sides of the panel enclosure on models so configured. I've seen more than a few panels with 1" or more insulation stripped off of both neutral and hot conductors. I've also seen cases where not enough insulation was stripped off and the binding terminal didn't sufficiently engage the conductor, causing arcing within the panel.

I haven't found a DIY book yet that explains in enough excruciating detail how to wire a panel without endangering your family, neighborhood, and rescue personnel. It's ironic to me that my state won't let a homeowner repack a faucet but they can rewire their entire house. Wow.

[Jerry Peck]

It's ironic to me that my state won't let a homeowner repack a faucet but they can rewire their entire house. Wow.


You know how many people drown in their own homes from working on their plumbing?

Wow! Zillions! :eek:

:D

[Jerry Peck]

Ah... a subsidiary panel. That would explain the "sub" in sub-panel. And here Jerry thought they were panels salvaged from submarines and sold at a discount in bog box stores.

It came from the fact that those panels are "sub-fed" panels, fed from "other" "panels" by feeders off a breaker in those other panels, and those "sub-fed" panels can feed other panels, and, those "sub-fed" panels can also be "sub-fed" from "service equipment with panel boards in the same enclosure, i.e., "service panels".

In fact, in many cases, the "sub-fed" panel is "the main panel" in the distribution system, becoming "the main panel".

Nonetheless, though, *ONLY* the service equipment has a neutral bonded to the ground *whether or not* the "service equipment" includes "a panelboard" within its enclosure.

"Sub panels" are found in "submarines".

"Main panels" are found only in "Maine".

Thus, if I run my "submarine panel" off my "Maine panel", I suspect my submarine is not going to get very far before I pull some wires loose and lose power.

:D

[Jorge Suarez]

Thanks for all the info. I see this is an old thread, but i hope someone will reply.

I know that the sub panel need to have isolated ground and neutral. but even though they are isolated in the subpanel, both lines run back to the main panel where they do touch. so are they really isolated?

[Jerry Peck]

Thanks for all the info. I see this is an old thread, but i hope someone will reply.

I know that the sub panel need to have isolated ground and neutral. but even though they are isolated in the subpanel, both lines run back to the main panel where they do touch. so are they really isolated?

Jorge,

Do a search here on "subpanels" and "sub panels" and you will find some really lively discussion regarding them, such as ... they are all "panels" and "all panels are wired the same".

What you are really asking is, with the neutral bonded to ground AT THE SERVICE EQUIPMENT, is the neutral really isolated from ground AT THE NOT-SERVICE EQUIPMENT panels, and the answer is ... 'Yes - AT THE NOT-SERVICE EQUIPMENT panels, the neutral truly are isolated from ground.'

The neutrals ARE ONLY BONDED TO GROUND AT ...

... SERVICE EQUIPMENT ...

... NOT AT any other panel at any other location.

By the way, welcome aboard, but you really should be thinking in terms of "service equipment" and "not service equipment" and the latter ("not service equipment") are simply "panels".

With that basic understanding and knowledge, then it is real easy to remember that the neutral IS ONLY bonded to ground at ... "service equipment", and if the equipment is not service equipment, but a panel, then the neutral IS NOT bonded to ground at the panel.