Clarification of 250.32

[cseckland]

I need a clarification of 250.32(B) Exception requirement (2):

There are no continuous metallic paths bonded to the grounding system in each building or structure involved.

This article allows the grounded conductior to be used in place of a ground, and be connected to the disconnecting means, grounding electrodes, and the equipment grounding system of the "grandfathered" structure or structures, provided three requirements are met. The second one is written above. I understand 1 and 3, (no ground ran, no GFP on supply side) but I'm unclear on 2. Any help?

Chris

 

[iwire]

First it does not just apply to existing buildings, up until the adoption of the 2008 NEC you could use 250.32(B)(2) for new construction.


As far as the metallic paths that can be anything like a copper water line from one building to the other or the shield of a coax cable.

Both of the above items would be bonded at both buildings and would end up carrying some of the neutrals current.

 

[cseckland]

So #2 is about any paths between buildings then? And if all three requirements are met I can and must bond the neutral to the equipment grounding sytem of the structure?

Chris

 

[iMuse97]

You are correct.

1. As Bob mentioned, the requirement of 250.32(B)(2) refers to any metal path that does exist between the buildings. This is a crucial safety issue: If there were a ground fault and some other metal path were available and were carrying an on-going fault current, many dangerous situations could result, as you can imagine. 2. As a result, to avoid those types of problems, if there is a metal path between the buildings you may not bond the EGC to the grounded conductor.

2. If all three requirements are met, you must make the bond.

 

[iMuse97]

Let me ammend my other comment: If there were other paths between the buildings, and the neutral was bonded, those paths would use that bond to become a path for a portion of the neutral current, as Bob mentioned, and this could cause many types of problems as well.

 

[tryinghard]

So #2 is about any paths between buildings then? And if all three requirements are met I can and must bond the neutral to the equipment grounding sytem of the structure?

Chris

No, if all three requirements are met plus the fact the premises wiring system is existing, then it is permitted not required. This is an exception to allow but the rule is no bonding past the service disconnect 250.24(A)(5) & 250.142(B)

It?s any bonded paths, but what?s critical is not installing a parallel path for neutral current on anything other than a conductor.

 

[cseckland]

250.32

250.32

Alright, thanks for the info everyone, I'll go forth and install properly...

 

[mka]

I have a similar situation

I have a similar situation

First it does not just apply to existing buildings, up until the adoption of the 2008 NEC you could use 250.32(B)(2) for new construction.


As far as the metallic paths that can be anything like a copper water line from one building to the other or the shield of a coax cable.

Both of the above items would be bonded at both buildings and would end up carrying some of the neutrals current.

So, you're saying that the two buildings if sharing the same water line need a GES at each building and the H2o needs to be a part of the GES and bonded at each building?

mka

 

[LarryFine]

So, you're saying that the two buildings if sharing the same water line need a GES at each building and the H2o needs to be a part of the GES and bonded at each building?

Correct, and that's why the neutral cannot be bonded in both places.