680.25(b)

[tincan44]

What is the reasoning behind requiring the feeder to have an INSULATED EGC to a NEW pool sub panel?

I understand conduit for feeders to a new pool panel are required. Existing panels for new pools meet 680.25 Exception.

I searched Mike Holt's site and read all the posts to try and find the answer as well as the commentary in the 2005 NEC Handbook and Soares '04.

Only Pierre Belarge took a guess "I am not positive, but I think it is because of the deteriorating effects of chlorine on the NM cable sheath."

Does anyone know for sure?

 

[peteo]

I am not sure either. The corrosion issue is brought up in washdown areas, etc.

This is a very interesting question. I?ve practically ignored 680, since all the jurisdictions around here have their own published set of requirements, somewhat more stringent than 680. This article was rewritten for an intuitively obvious, and very important, reason.

The original change to the 2002 was intended to prohibit currents, i.e. the chance of using the earth as a conductor. Say this quick three times:
"Pool equipment with conductive surfaces connected to a panel supplied with a feeder utilizing a common grounded and grounding conductor will be subjected to continual surface voltage fluctuations depending on voltage drop stemming from the varying amount of neutral current flowing through the grounded conductor. These fluctuations pose a safety problem in a pool environment.?
A quote from some highlighted text here, down on page 33/535:
http://66.102.7.104/search?q=cache:OeNDEuvddCcJ:www.nfpa.org/assets/files/pdf/550_700C.pdf%3Fsrc%3Dnecdigest+wording+in+the+next+subsection+%5B680.25(B)(2)%5D+to+assure&hl=en&gl=us&ct=clnk&cd=1

It seems that they caught themselves, as the above only discusses separate structures. What about a pool inside the house? Here?s a page which points to something related, and more recent, but my PC can?t do it. Please let me know, if there?s something meaty here.
http://www.google.com/search?hl=en&lr=&q=www.nfpa.org%2Fassets%2Ffiles%2F+pdf%2FNECPart4.pdf+680.25%28b%29%282%29&btnG=Search

 

[bphgravity]

I have been researchng this very issue to no avail. I would have no problem with the requirement and accept it is for the reduction/prevention of stray currents on the grounding system, however the exception to this section throws the safety concern out the window.

If SE cable or other cable types are not permitted for new work because the use would be unsafe, what happens once the work is existing that makes it safe? It appears the only qualifier for this exception is when the work is performed and not what steps have been made to make it equvalently safe.

 

[Pierre C Belarge]

What I have been learning from some of my reading is that the safety aspect of wiring for pools is the big item. The use of a raceway for the wiring is to give the conductors the greatest amount of protection from physical damage as is possible.
Maybe the same thing is for insulated EGC... the insulation will help to lession the chances of incidental contact with a live conductor or maybe even the stray voltage that sometimes is present.

 

[tincan44]

I have done a lot of reading on this issue with the links provided by Peteo and most of it wants to direct you back to 250.32. There is also a discussion of the corrosive environment on devices and connections.

I Red Taged a new pool subpanel last week. The EC ran a #4 w/g NM & installed a 100A breaker. I pointed out the violations of 334.80, 310.16 and 680.25(A & B). He was pretty upset but agreed to change these items and wanted to know why the EGC had to be insulated.

Maybe the answer is a combination of 'voltage fluctuations pose a safety problem in a pool environment' and providing 'maximum protection' of the EGC.

Simply stating 'the Code requires it' does not offer any understanding.
Sure wish I had something solid to 'hang my hat on.'

 

[BarryO]

'maybe a little off-topic, but there's another Article that requires an insulated grounding conductor (820). 'never understood that one, either.

 

[peteo]

Barry, the point of 820 in my 2002 handbook is touched on in the explanatory material after article 250.94 and on page 19 of Mr. Zipse's article. Unless i misunderstand.

Our host has provided excellent reference material. Specific to what I believe the intent is, which is providing the new for 2005 equipotential plane so as to avoid stray voltages, here are some articles and references. The one most directly relevant to 'why,' would possibly be the last:

2002 new NEC references to equipotential planes:
http://www.ecmweb.com/mag/electric_code_changes_5/index.html
2005 NEC article 680:
http://www.ecmweb.com/mag/electric_grounding_vs_bonding_11/index.html
several places to start reading about the issue in general, with a couple 'pool shock' stories:
http://www.mikeholt.com/technical.php?id=strayvoltage/technicalstrayvoltagenewslettersmenu
and finally a barnstormer of an article by Donald Zipse. It is referenced on the above page. If you wish to skip the history and theory, and get the parts more germaine to pools, simply read the bolded text and what accompanies figures 18 and 19. The objective would be to answer the question, why an insulated EGC.
http://www.mikeholt.com/documents/strayvoltage/word/MultiGroundedNeutralFinal5-3-03.doc

 

[tom baker]

Perhaps insulation is required for corrosion protection. It may be as simple as that.