Bonded again at 'main panel'?

[Terry Beck]

Would like some support if I'm right, and correction if I'm wrong. About to enter a discussion with an electrician over this. Would appreciate response as soon as possible.

Meter and service entrance panel are installed on exterior of house. This panel is grounded and bonded.

Inside the wall is the "main panel' (or what I would call the main distribution panel). Three conductors come in through the back of the panel, the 2 hot service conductors, the 3rd service neutral, AND a bare grounding wire that attached to the left bus bar - which is attached to right bus bar, which has a bonding jumper to back of the panel enclosure. Equipment grounding conductors and neutrals terminate at both busses. To me, this means that this 'sub panel' (main distribution panel), has been bonded a second time.

Hitch - it has been approved the that local state electrical inspector (now retired), and the current state electrical inspector approves this setup on a regular basis - so I am told by the electrician.

See pics.

Now - is anything wrong with this picture(s)?
IF it is wrong, then what is the danger?

Please - also drop some code references. I am going through NEC 2005 section 250 again, but could use some help interpreting the code language.

Thanks ahead of time
Terry Beck

[Jerry Peck]

You are correct - the interior panel needs to have the neutrals isolated from ground, not only by removing that bonding jumper but also the grounds and neutrals need to be in separate terminal bars, with the neutrals terminal bar isolated from ground.

[Terry Beck]

Thanks Jerry (I'd hoped you were around).

Can you tell me which section of the NEC refers to isolation of grounding and grounded conductors at sub panel? And where in NEC is the sub panel defined? I've been going through section 250 and can't seem to find it.
(I'm using NEC 2005 because that's that age of the house).

[Terry Beck]

Is it all based on 250.6(A)?
"Arrangement to Prevent Objectionable Current.
The grounding of electrical systems, circuit conductors,
surge arresters, and conductive non-current-carrying materials
and equipment shall be installed and arranged in a
manner that will prevent objectionable current over the
grounding conductors or grounding paths."

[Terry Beck]

How about 250.24 (A)System Grounding Connections. A premises wiring
system supplied by a grounded ac service shall have a
grounding electrode conductor connected to the grounded
service conductor, at each service, in accordance with
250.24(A)(l) through (A)(5).

(5) Load-Side Grounding Connections. A grounding
connection shall not be ma~e to any grounded conductqr on
the load side of the service disconnecting means except as
otherwise permitted in tris article.'

FPN: See 250.30(A) for separately derived systems,
250.32 for connections at separate buildings or structures,
and 250.142 for use of the grounded circuit conductor for
grounding equipment.

and

408.40 3rd paragraph
Grounding conductors shall not be connected to a terminal
bar provided for grounded conductors (may be a
neutral) unless the bar is identified for the purpose and is
located where interconnection between equipment grounding
conductors and grounded circuit conductors is permitted
or required by Article 250.

Getting closer?

My theory is weak. Can anyone provide some some clarification on what is the real danger of a main distribution panel being bonded when the service entrance panel is 6 inches away on the exterior side of the wall? Some of this seems somewhat arbitrary. It makes good sense in panels in detached buildings.

[ken horak]

by bonding the neutral down in more then one place you have created a parallel path for the neutral currents to flow on.
Electricity is always seeking its way to it's SOURCE. In this case that is the power companies transformer. The path it takes is across the neutral conductor.
Now in the case of the sub-panel with the neutral bonded to the ground, the neutral currents have 2 paths of travel for the returning current.
Path # 1 is the neutral conductor going back to the distribution panel ( main service panel)
Path #2 is the ground conductor and any metallic parts involved with the sub panel.
The sub panel can, any metallic conduits, etc now have the potential to become electrified.

[Jerry Peck]

Can you tell me which section of the NEC refers to isolation of grounding and grounded conductors at sub panel? And where in NEC is the sub panel defined?


The reason you cannot find anything about sub panels is because you need to look at my avatar to see a sub panel. :D

There is nothing in the NEC which defines what a sub panel is because the NEC does not relate to submarines - what you are referring to is a panel which is "not service equipment".

There are two types of panels, ones which are "service equipment" and all others. The one you are referring to is one of the "all others", or "not service equipment".

The neutral is ONLY bonded to ground at the "service equipment", no place else.

- 250.24 Grounding Service-Supplied Alternating-Current Systems.
- - (A) System Grounding Connections. A premises wiring system supplied by a grounded ac service shall have a grounding electrode conductor connected to the grounded service conductor, at each service, in accordance with 250.24(A)(1) through (A)(5).
- - - (5) Load-Side Grounding Connections. A grounded conductor shall not be connected to normally non–current-carrying metal parts of equipment, to equipment grounding conductor(s), or be reconnected to ground on the load side of the service disconnecting means except as otherwise permitted in this article.
- - - - FPN: See 250.30(A) for separately derived systems, 250.32 for connections at separate buildings or structures, and 250.142 for use of the grounded circuit conductor for grounding equipment.
- - (C) Grounded Conductor Brought to Service Equipment. Where an ac system operating at less than 1000 volts is grounded at any point, the grounded conductor(s) shall be run to each service disconnecting means and shall be connected to each disconnecting means grounded conductor(s) terminal or bus. A main bonding jumper shall connect the grounded conductor(s) to each service disconnecting means enclosure. The grounded conductor(s) shall be installed in accordance with 250.24(C)(1) through (C)(3).
- - - Exception: Where more than one service disconnecting means are located in a single assembly listed for use as service equipment, it shall be permitted to run the grounded conductor(s) to the assembly common grounded conductor(s) terminal or bus. The assembly shall include a main bonding jumper for connecting the grounded conductor(s) to the assembly enclosure.

I.e., the grounded conductor shall be run to the service equipment, and the grounded conductor shall be bonded to the enclosure (ground) at the service equipment (all on the line side of the main service disconnect), and the grounded conductor shall not be grounded on the load side of the service disconnect (not at any location or panel downstream from the service equipment).

If the grounded conductor is grounded at any point or points down stream of the service equipment, that WILL cause the equipment grounding system to carry a share of the current the grounded conductor would otherwise be carrying, and the equipment grounding system IS NOT FOR THAT PURPOSE, that practice can kill people, and cause other problems.

[Terry Beck]

Thanks Ken,

I understand the idea that current will seek any path. But I guess I'm still fuzzy. Will keep working on it

[ken horak]

The reason you cannot find anything about sub panels is because you need to look at my avatar to see a sub panel. :D



That is wrong also ! Your advatar may be a picture of a submarine and an electrical panel, but that is not a SUBPANEL.

If you insist on beating this dead horse until it's only dust left, then at least use the correct terminology in your references.

What you insist on calling a sub panel is a " marine panel".:eek:

Based on the Ul White Book :D

[Jerry Peck]

That is wrong also ! Your advatar may be a picture of a submarine and an electrical panel, but that is not a SUBPANEL.

That is why I said SUB PANEL (note the space to designate "SUB" for "submarine" and then "PANEL" for the panel in the submarine.


If you insist on beating this dead horse until it's only dust left, then at least use the correct terminology in your references.


It is not beating a dead horse as most misunderstandings result from not recognizing that there is "service equipment" and "other than" "service equipment" panels, and that the neutral (the grounded conductor) is only bonded to ground at the "service equipment" and not at "other than" "service equipment" panels.

As they throw that last shovel full of dirt over me I will reach up and explain to them that there is "service equipment" and "other than" "service equipment" panels and the the neutral is only bonded to ground at "service equipment" panels ... that is if they do not freak out and run away when they see may hand coming up and grabbing them by the collar ... :eek:

[James Duffin]

Terry...

Check section 250.32 (B) in the 2008 code.



250.32 Buildings or Structures Supplied by a Feeder(s)
or Branch Circuit(s).

(A) Grounding Electrode. Building(s) or structure(s) supplied
by feeder(s) or branch circuit(s) shall have a grounding
electrode or grounding electrode system installed in
accordance with Part III of Article 250. The grounding
electrode conductor(s) shall be connected in accordance
with 250.32(B) or (C). Where there is no existing grounding
electrode, the grounding electrode(s) required in 250.50
shall be installed.


Exception: A grounding electrode shall not be required
where only a single branch circuit, including a multiwire
branch circuit, supplies the building or structure and the
branch circuit includes an equipment grounding conductor
for grounding the normally non–current-carrying metal
parts of equipment.


(B) Grounded Systems. For a grounded system at the
separate building or structure, an equipment grounding conductor
as described in 250.118 shall be run with the supply
conductors and be connected to the building or structure
disconnecting means and to the grounding electrode(s). The
equipment grounding conductor shall be used for grounding
or bonding of equipment, structures, or frames required
to be grounded or bonded. The equipment grounding
conductor shall be sized in accordance with 250.122.
Any installed grounded conductor shall not be connected
to the equipment grounding conductor or to the grounding
electrode(s).


Exception: For existing premises wiring systems only, the
grounded conductor run with the supply to the building or
structure shall be permitted to be connected to the building
or structure disconnecting means and to the grounding
electrode(s) and shall be used for grounding or bonding of

equipment, structures, or frames required to be grounded
or bonded where all the requirements of (1), (2), and (3)
are met:
(1) An equipment grounding conductor is not run with the
supply to the building or structure.
(2) There are no continuous metallic paths bonded to the
grounding system in each building or structure involved.
(3) Ground-fault protection of equipment has not been installed
on the supply side of the feeder(s).
Where the grounded conductor is used for grounding in
accordance with the provision of this exception, the size of
the grounded conductor shall not be smaller than the larger
of either of the following:
(1) That required by 220.61
(2) That required by 250.122

[Joe Driscoll]

I'm having trouble seeing the service equipment in the photos given, I see what may be a meter socket, but no means of disconnect there, I see lugs for the hots, and a buss for the neutral and grounds.... any chance a clearer full picture of outdoor panel?

[James Duffin]

It looks like it may be a feed-though panel with a main breaker at the top out of the picture.