NEC 250.32(B)(2) electrocutes people

[ramsy]

It appears NEC 250.32(B)(2) advocates an electrocution hazard in all code cycles, including the 2008 exception for existing premises.

Where no EGC exists at loadside feeders NEC instructs contractors to bond neutral for fault-current path, as long as no objectionable current flows.

..there are no continuous metallic paths bonded to the grounding system in each building

The electrocution potential exists --without objectionable current flow-- when separate-structure-plumbing grids bond to primary services.

So anyone --like soldiers in Iraq-- that touch this bootlegged equipment to plumbing fixture can be electrocuted. As loads charge EGC's with neutral current in subpanel, GFCI mechanisms are defeated by parallel paths of people shorting electrical-equipment housings to the common-plumbing grid.

 

[charlie]

. . . when separate-structure-plumbing grids bond to primary services. . .

If I understand you, the plumbing goes back to the first building and that is violating the NEC in this section. :-?

 

[ramsy]

the plumbing goes back to the first building and that is violating the NEC in this section. :-?

Yes, that's the problem I see. Separate-structure electrode is not required to be bonded to plumbing, 250.32(A) Exception.
Can't be bonded without creating objectionable current.

 

[roger]

I agree with Charlie, but it is a moot point in the 2008 NEC anyways.

Roger

 

[charlie]

That is the problem when the NEC (a safety code) is violated. The separate building should have a neutral and a grounding conductor run to it. Additionally, the grounding electrodes are to be installed and connected to the grounding bar in the panelboard and not to the neutral. :smile:

 

[ramsy]

That is the problem when the NEC (a safety code) is violated.

Where does the separate-structure plumbing grid violate the NEC?

The 250.32(B)(2) neutral bond is legal for fault path.

Both combine for an electrocution hazard in all code cycles, including the 2008 250.32(B) exception, for existing premises.

 

[C3PO]

If you have a common plumbing grid between the buildings then you would have a violation and could not just run a grounded conductor. So the NEC is not advocating that.

 

[C3PO]

Where does the separate-structure plumbing grid violate the NEC?

The 250.32(B)(2) neutral bond is legal for fault path.

Both combine for an electrocution hazard in all code cycles, including the 2008 250.32(B) exception, for existing premises.

The NEC is violated because with a common plumbing grid you have a "continuous metallic paths bonded to the grounding system in each building or structure involved"

 

[ramsy]

If you have a common plumbing grid between the buildings then you would have a violation and could not just run a grounded conductor. So the NEC is not advocating that.

I can't find this reference. Any pointers?

 

[ramsy]

The NEC is violated because with a common plumbing grid you have a "continuous metallic paths bonded to the grounding system in each building or structure involved"

See post #3, its not "bonded to the grounding system" when the plumbing is isolated from the separate-structure electrode.

This isolation between "plumbing" and "electrode" is legal, and required to avoid objectionable current, therefore, the electrocution potential exists between the two.

 

[charlie]

. . . This isolation between "plumbing" and "electrode" is legal, . .

How do you get around 250.104(A)(3)? :-?

 

[ramsy]

How do you get around 250.104(A)(3)? :-?

The NEC gets around this with its 250.32(A) Exception, as noted in post #3, just before making what appears a historical error, by advocating separate-structure feeds without grounding in 250.32(B)(2)

The electrocution potential is historically advocated by the NEC, by allowing neutral bonding at the subpanel.

This is a serious NEC error, and I would not be surprised if fatalities are associated with it.

 

[C3PO]

The NEC gets around this with its 250.32(A) Exception, as noted in post #3, just before making what appears a historical error, by advocating separate-structure feeds without grounding in 250.32(B)(2)

The electrocution potential is historically advocated by the NEC, by allowing neutral bonding at the subpanel.

This is a serious NEC error, and I would not be surprised if fatalities are associated with it.

This is what 250.32(A) exception says:
Exception: A grounding electrode shall not be required where only a single branch circuit supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the conductive non?current-carrying parts of equipment. For the purpose of this section, a multiwire branch circuit shall be considered as a single branch circuit.



First of all this is only permitted if you have one branch circuit. So you wouldn't have a subpanel. Second you have to run an EGC.

 

[charlie]

I am having difficulty with your statements. In the past, "it left as a feeder and arrived as a service" was pretty good until we realized that a continuous metal path made the installation suspect. The water piping system was always required to be bonded so there was no more danger that a normal service from the electric utility. However, there was current from the unbalanced load going back into the first building. Therefore, the code was changed to what we have in the 2008 edition. Prior to that (somewhere around the 1993 Edition), where a continuous metallic path existed, the grounds and neutral were to be kept separate at the second building and the grounding and bonding was to the grounding bar and not the neutral. The problem was that not very many people were doing it that way.

 

[ramsy]

First of all this is only permitted if you have one branch circuit. So you wouldn't have a subpanel.

OK, if not 250.32(A) then 250.6(A), you can't bond if objectionable current exists. So, large feeders are also permitted without bonding if we can't create two paths for neutral current across conductor & plumbing.

Therefore the electrocution potential --neutral/egc to plumbing-- has been permitted by 250.32(B)(2) in error.

Here's my example:

1) Feeder is 3-wire 240v #6 mwbc in RMC.
2) The conduit EGC is lost with an aerial between structures, as permitted:
Messenger (bare neutral) supporting two phases, per 250.184(A)(1).
3) Subpanel properly bonded to neutral --with all circuit EGC's-- per 250.142
4) Separate-structure plumbing is properly isolated from subpanel per 250.6

Now everything is NEC compliant, but supanel-occupant gets shocked touching toaster and kitchen sink, or other appliances when floor gets wet.

This parallel path from neutral charged appliances should never have been permitted. If this code section is not in error, then it has clearly permitted omitting EGC's and the hazardous consequence of bonding neutrals at subpanels.

 

[don_resqcapt19]

Roger,
If this is such a big hazard, why is the service not the same hazard? The rebonding of the neutral and connection to a grounding electrode at a second building is exacty what happens at a service. How is one safe and the other a huge hazard?

 

[infinity]

Now everything is NEC compliant, but supanel-occupant gets shocked touching toaster and kitchen sink, or other appliances when floor gets wet.

This parallel path from neutral charged appliances should never have been permitted. If this code section is not in error, then it has clearly permitted omitting EGC's and the hazardous consequence of bonding neutrals at subpanels.

Roger,

I'm confused, what does bonding the neutral at the panel have to do with getting a shock from the toaster and sink? As Don mentioned is this any different than a service?

 

[charlie]

. . . Now everything is NEC compliant . . .

Not the way you are doing it. You can not isolate the plumbing in accordance with 250.6 and ignore "250.6(B)(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, provided that the requirements of 250.4(A)(5) or (B)(4) are met:"

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

 

[iwire]

Roger,
If this is such a big hazard, why is the service not the same hazard? The rebonding of the neutral and connection to a grounding electrode at a second building is exacty what happens at a service. How is one safe and the other a huge hazard?

\

Thank you for stating exactly what I was thinking. :smile:

 

[ramsy]

Roger,
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?

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.