Open-Neutral Protection

[finhead]

Section 680.33(B)(4) mandates a ground-fault circuit interrupter with open-neutral protection for fixtures over 15 volts in a storable pool.

Does anyone understand how open-neutral protection works?

Also, this requirement is for storable pools only. A similar pool with metallic walls, but over 42 inches in height, is not subject to the same requirement. Does anyone see the logic here?

Thanks

 

[NoVA Comms Power]

Two theories of my own (which would both require a EGC):

One way might simply be when the line-to-EGC voltage is above a certain point, AND the line-to-neutral voltage is below a certain point.

Another way might be some sort of circuitry which can detect an "open" on the normally completed "loop" thru the EGC and main bonding jumper back to the "line neutral" terminal of the GFCI

I'd be interested in knowing for sure too.

 

[winnie]

I think that you will find that portable GFCI devices incorporate open neutral protection. In particular, you can get GFCI cord caps that have the required open neutral protection.

Here is a page from the IAEI News that I found (not dated, *grrr* but I suspect 2000) which says that portable GFCI devices must incorporate open neutral protection, but fixed GFCI devices do not need to do so. There is some discussion of why this is only required for portable applications.
http://www.iaei.org/subscriber/magazine/00_b/ul_question.pdf

IAEI News discussion of GFCIs, including open neutral protection:
http://www.iaei.org/subscriber/magazine/00_f/casparro.htm

Here is the P+S catalog for their GFCI cords and cord caps, which specifically describes the open neutral protection:
http://www.passandseymour.com/pdf/E10-E13.pdf

Hubbell markets a hard wire GFCI unit (not a receptacle) which incorporates open neutral protection. See page 11 of:
http://www.hubbell-wiring.com/Press/PDFS/Section-H.pdf

For single pole circuits, the easiest way to have 'open neutral' protection is to have some sort of contactor or relay that is held open by the supply voltage. Lose the neutral, and you no longer have supply for the relay, and the contacts open. You will not that some of these cord connected GFCI devices need to be reset every time they are plugged in. But I don't know if this is actually how they work.

-Jon