I recommissioned a pool light that hadn't been used in years. I purchased a new 500W Pentair light and fished its cable back to the original junction box. I changed the old GFI to update that protection. I found a #8 grounding wire attached to stake next to that junction box, and I confirmed continuity between that stake, the pool wet niche, the sealing ring, and the light chassis. The junction box is confirmed to be located above the pool deck and waterline. The pool light works -- my only question is whether or not there are any other safety tests that I can or should perform.
I also installed a "Cord Stopper" product at the back of the niche which is designed to create a seal around the light cord and at the electrical conduit. I know the conduit is supposed to be able to tolerate water, but I'd prefer to keep it dry for a number of reasons.
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If I am not mistaken, you need to run that #8 bonding conductor back to your deck box from the forming shell. Tying it to your pool bonding grid is also required but it sounds like you have that already sorted out.
This is in addition to the ground wire in the pool light's cord.
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I think we're on the same page. What I refer to as the "wet niche" is a stainless steel cannister (your "forming shell") that the Pentair light assembly fits into. The trick is that the niche is already installed, attached to the pool wall, covered by a concrete deck, diving board, etc. I can't really tear up the entire deck to prove that the #8 grounding wire is attached to rear of that niche. However, that's why I tested the continuity between that grounding stake and the front of the wet niche that I can access. Since it has continuity, I have to assume that the rear connection is intact. Is that conclusion safe, or would that be the case for any metal housing that comes in contact with the earth?
As for being tied to the "bonding grid", does that refer to what I call the grounding loop that attaches to the metal wall braces, ladder insert cups, etc.? If so, I know of at least one independent location where I could test for continuity between that ground loop and either the stake next to the junction box or the niche itself.
I try to be conscientious about safety, so I appreciate the help. It sounds to me like I'm covering all the bases that can be tested, but it sure helps to hear a second opinion.
PS: Which item provides more protection -- the grounding wire or the GFI? And as an engineer, can you tell me in layman's terms why the grounding wire for the niche serves a different purpose than the grounding wire for the light?
You should have a conduit running back from the "wet niche" to the deck box - it is the conduit with you light's wiring in it. The bonding wire should be in that pipe and bonds the niche to ground potential for the entire system.
I think we both agree that the niche is already bonded to the grounding grid in your deck. You still need that #8 bonding conductor back to the deck box.
The niche should have two grounding lugs - one on the back (usually) which you can't see now and one visible. The #8 runs from there.
Bonding the niche to your grid puts the niche at the same ground potential as the grid but the additional #8 goes (essentially) back to the GFI - you terminate the #8 at the deck box which is grounded back to the GFI.
The GFI provides almost instantaneous interruption of current to your system - a traditional thermal magnetic breaker is quite slow in comparison. You need both the GFI and the bonding wire. This is in addition to the ground wire already in your light cord.
This is code. If you are getting this set up inspected, you need that #8. If you ever sell you home, the inspector may or may not look for it.