NEC 250.32(B)(2) electrocutes people

[iwire]

Objectionable current is the only reason given for generally prohibiting neutral bonds to the subpanel EGC in NEC 250.6, 250.32, 250.142. However, if human bodies are assumed to provide ~500 ohms resistance to voltage (HardtoFindVolume2.pdf), parallel-neutral paths approaching 0.1A at 50+vac (ventricular fibrillation) is not examined, before 250.32(B)(2) creates the potential of parallel load paths.

Where feeder EGC's are exceptioned 250.184(A), green-fault path uses white neutral 250.32(B)(2), and bonding objectionable current paths are prohibited 250.6, potentials exists for other return paths for load current. Plumbing with less resistance than subpanel/service neutral are not unusual with municipal plumbing grids.

Electrocution depends on human-parallel-resistance from energized-equip.frames to any plumbing grid, outdoor hose bib, temp. power, extension cords, new wiring additions, aluminum siding, roofing, wet feet, or other low impedance return path. Combine this energized grounding with open neutrals and the EGC-energized human is a series return path thru any of these objectionable potentials.

How about answering the question?

If this is such a big hazard, why is the service not the same hazard? ..How is one safe and the other a huge hazard?

 

[charlie]

Bad call

Bad call

Objectionable current is the only reason given for generally prohibiting neutral bonds to the subpanel EGC in NEC 250.6, 250.32, 250.142. . .

I don't understand how you think you can get by with disconnecting all the bonding connections.
250.6(B) Alterations to Stop Objectionable Current. If the use of multiple grounding connections results in objectionable current, one or more of the following alterations shall be permitted to be made, . .

None of the permissions permit anything other than the relocation of the bond connections and the disconnection of duplicate connections.

I am giving up on this thread. The way you are reading the Code will get someone killed if you are lifting the bonding from water piping systems.

 

[ramsy]

Not the way you are doing it. You can not isolate the plumbing in accordance with 250.6 and ignore "250.6(B)

I thought we had a solution here, but then I read 250.4(B)(4), which overrides 250.6(B) alteration #3.
The Entire-plumbing grid must bond at service point, it can't be split or isolated to remove the objectionable, 2nd-current path, to service entrance point. Alteration #1,2 & 4 would not remove 2nd current path (in plumbing).

We must be permitted to remove the 2nd current path before bonding to it, these specific alterations don't solve that issue directly. The entire plumbing grid is already bonded at the service, as required. I don't see the separate-structure electrode bonding to that plumbing, without going above and beyond NEC requirement, or once again soliciting the input of local-AHJ policies.

You are still required to bond the water piping system. The plumbing system can not be properly isolated . . . period. :smile:

I believe adding a feeder EGC and removing loadside-neutral bond is the solution, but the NEC does not clarify this in 250.6(B) or anywhere else.

At no fault of the original efforts brought by you fine people, relying on this document alone is a time consuming effort for me, and for you, some of the most involved NEC users located thru out the NEC's global jurisdictions.

I believe you were great, but the NEC errors for the following reasons:

1) As defined earlier, the document appears to advocate placing people between energized equipment (EGC) and multiple-common paths for electrocution.

2) Solutions to this section do not readily present reasonably-clear, or code-compliant method to remove this hazard, short of blasting permits, demo, rebuild to remove bonding grids and filling building crater with engineering supervised re-design & plastic plumbing.

3) Abating this electrocution hazard requires a paradigm shift where production must be interrupted to occasionally address NEC confusion, conflict, or perhaps historical code-cycle error / Exceptions of 250.32, 250.142, etc, where neutral bonding at load-side equipment grounding, occurs loadside, at separate-structures, and perhaps beyond.

4) With many local AHJ's adopting international standards, I believe this trend should be the furture. Many European-electrical codes standardize on IEEE entirely in the public domain, --consolidating rainbow-book equivalents (proprietary and otherwise inaccessible)-- to ASCI STD dependent contractors like me.

5) The last vertue IC's needed with the NEC was Grounding and Bonding methods, unique to North American systems. Seeing the NEC community effort needed to extract clear solutions to Grounding and Bonding methods, a large nail is driven in this coffin. I'm ready to adopt another standard. You people are likable, amazingly tolerant, and diligent by responded to this challenge, but the opportunity cost talent must spend addressing this issue kills every aspect of productivity.

 

[iwire]

Roger, can you passably be a bit more concise, I can not make heads or tails out of your post.

 

[don_resqcapt19]

The entire plumbing grid is already bonded at the service, as required. I don't see the separate-structure electrode bonding to that plumbing, without going above and beyond NEC requirement, or once again soliciting the input of local-AHJ policies.

A grounding electrode is required at the second building and if the water pipe feeding the second building is a metal under ground water pipe then it must be used as a grounding electrode. If it is not used a grounding electrode, 250.104(A)(1) would still require the bonding of the metal water pipe at the second building.

I believe adding a feeder EGC and removing loadside-neutral bond is the solution, but the NEC does not clarify this in 250.6(B) or anywhere else.

The 2008 requires exactly that for new installations and the previous codes have required that if there were any conductive paths between the two buildings other than the feeder circuit conductors.