2008 250.32 ( B )

[IRAQ TIGER]

I have 10 separate buildings each with its own interior panel, they are all fed from a common sub panel. As I understand 250.32 ( B ) each building must be bonded from the interior panel by its feeders EGC this jumper must be sized by 250.66 and connected to a electrode system. Please confirm the above described installation for me.

What code article would be violated if the bonding of the 10 separate buildings was accomplished from the sub panel that powers all 10 units, instead of bonding from each interior panel?

 

[kwired]

I have 10 separate buildings each with its own interior panel, they are all fed from a common sub panel. As I understand 250.32 ( B ) each building must be bonded from the interior panel by its feeders EGC this jumper must be sized by 250.66 and connected to a electrode system. Please confirm the above described installation for me.

What code article would be violated if the bonding of the 10 separate buildings was accomplished from the sub panel that powers all 10 units, instead of bonding from each interior panel?

250.32(A) requires a grounding electrode system at each of the 10 separate buildings. It must be installed according to (B) or in the case of an ungrounded system (C).

 

[infinity]

Since you're under the 2008 each separate building will require it's own GES (grounding electrode system) which could be two ground rod's if no CEE or metallic water pipe electrodes are present. The GES will be connected to the ground bus (not the neutral bus) in the panel within each building. The feeders for each building will require a separate EGC included in the feeder and isolated from the neutral at each building.

 

[IRAQ TIGER]

So the only way to be properly code compliant for a remote building is the following.

1 - The building must be bonded to the EGC of the feeder supplying power to the facility

2 - The bonding jumper must be sized to table 250.66

3 - A grounding electrode system must be established for each separate building

4 - The grounding electrode conductor must be sized to 250.66

 

[Smart $]

So the only way to be properly code compliant for a remote building is the following.

1 - The building must be bonded to the EGC of the feeder supplying power to the facility

2 - The bonding jumper must be sized to table 250.66

3 - A grounding electrode system must be established for each separate building

4 - The grounding electrode conductor must be sized to 250.66

1) Correct and EGC sized to Table 250.122.

2) What bonding jumper?

3) Correct.

4) Correct (and I make note that you did not reference the section-corresponding table).

 

[IRAQ TIGER]

Remote buiding / office trailers

Remote buiding / office trailers

1) Correct and EGC sized to Table 250.122.

2) What bonding jumper?

3) Correct.

4) Correct (and I make note that you did not reference the section-corresponding table).

I have the following conditions which I believe that my description below is the only code compliant installation. I have a fellow worker that believes I am incorrect with my interpretation of the NEC 2008 for this installation.

1 - I have six separate metal office trailers on the same property.

2 - The six office trailers are powered from the same outdoor remote sub panel.

3 - The six office trailers are about four feet apart from each other.

4 - Each office trailer has it own feeder installed from the outdoor remote sub panel to the interior panel of each trailer.

5 - There is no metallic piping of any kind between the six metal office trailers.

6 - Each office trailer has a three phase interior panel with separate neutral and equipment grounding conductor bar and conductors.

I believe that the following applies to this installation.

A - NEC 250.32 ( B ) applies and describes the proper installation for the above listed conditions

B - Each trailer must be bonded from its interior panel that supplies it's power. 250.32 ( B )

C - Each trailer must be connected to a grounding electrode system. 250.64

D - The bonding jumper to the building steel must be sized to 250.66, according to 250.104 ( C )

E - The six trailers can be connected to a common grounding electrode system. 250.58, 250.64 ( D ) ( 1 )

F - The six trailers CAN NOT be BONDED from the remote sub panel that supplies power to all six units.

Feedback please.

 

[Smart $]

I have the impression these office trailers are of the mobile/manufactured home type. If that be the case, the requirements fall under Article 550. See 550.4(A) Mobile Home Not Intended as a Dwelling Unit.

As such, each trailer is required to have an outside, not-on-the-exterior disconnecting means located within sight of and not more than 30' from the exterior surface. If the subpanel meets the within sight and distance requirements, all is good. Otherwise, a disconnect switch must be installed to meet the requirements, and as long as the feeder ocpd are appropriately rated, the disconnect switches need not have ocpd.

Whether each trailer is required to have a grounding electrode system (GES) has been debated extensibly here without ultimate resolution. I am not going to try and persuade you either way, but on the side of those who believe a GES is not required at a trailer, you will have to run an insulated EGC with your feeders. The EGC is not bonded to the grounded neutral conductor anywhere (other than at the service or separately derived system disconnecting means supplying power to the subpanel).

 

[ActionDave]

B - Each trailer must be bonded from its interior panel that supplies it's power. 250.32 ( B )

F - The six trailers CAN NOT be BONDED from the remote sub panel that supplies power to all six units.

Feedback please.

I am unclear about what you are saying in these two points.

Each trailer needs separate grounded (meaning neutral for most of us most days of the week) and equipment ground conductors pulled to it and the neutrals isolated at each trailer.

250.32(B) Grounded Systems.
(1) Supplied by a Feeder or Branch Circuit.An equip-
ment 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 ground-
ing 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 equip-
ment grounding conductor shall be sized in accordance with
250.122. Any installed grounded conductor shall not be con-
nected to the equipment grounding conductor or to the
grounding electrode(s).