EGC on a 12V pool light

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TimB100000

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I've spent the evening looking at a few hundred posts on low-voltage pool light grounding (not bonding), and can't seem to find a satisfactory answer to this, even though the topic of pool lights has been covered extensively. I'm looking at a 12V pool light, and the cable from the lumiere includes a green ground wire. The light will be connected to a isolated-secondary transformer (Intermatic PX300) via PVC conduit. The transformer has an "Equipment Ground" lug, which is the transformer housing (mains ground.) I could connect the ground wire of the lumiere to the equipment grounding lug of the transformer, but that doesn't make any sense to me. Since there's no potential between either leg of an isolated secondary and mains ground, even if there was a dead short between one of the secondary wires to the metal housing of the fixture, no current is going to flow to mains ground. Perhaps if the transformer isolation failed, and mains current was flowing in one of the secondary wires, AND the lumiere allowed the secondary to short to the housing, a ground would help. But that risk seems lower than the risk that if there's a short to ground anywhere in my house, some amount of current will find its way into the pool area through that ground wire. If the resistance to ground through that path isn't much higher than resistance to ground via the panel, that current could be significant. Or if the pump ground became disconnected, that lumiere ground path might become the pump's ground path, which it was never intended to be. If I've got an isolated secondary, why would I want to introduce a mains-referenced ground? Am I missing something?

Tim
 
I have never seen an equipment grounding conductor on a 12v light fixture but I have never installed a 12v pooil light. The lug on the trany is to be connected to the equipotential bonding I suppose.

Maybe someone else has some thoughts on this or has seen it before.
 
I, as well, have not see a 12V pool light with a dedicated ground wire. I am familiar with Intermatic transformers, PX 100 and 300. Both exactly the same physically. Only difference is the transformer sizes off 100W and 300W.
They both have a ground bar for the feed. They do not have BOND lugs. A required deck/junction box with cord strain relief for the light itself, will have a ground bar inside and a bond lug on the outside. Interestingly enough, the Intermatic deck boxes I use, PJB series, the bond lug bolts through the box and connects to the ground bar inside.

TimB1000000, could you post the make and model of your pool light?
 
Thanks-- It's a Pentair Amerlite 12V/300W from around 2010. It definitely has a 3 wire cord (black, white,green) and the assembly instruction manual (which the customer still has, amazingly) is the same for both the 120V and 12V versions, and says to connect all three wires, which obviously makes sense for a 120V light. The manual doesn't say anything about whether the ground should be eventually connected to the grounding bar at the transformer. I'm still questioning what function a mains ground has on a 12V isolated circuit, and the safety when that (useless) mains ground connection might create a current path out the pool from a fault somewhere else in the residence. Seems like a case where more-grounding-is-better isn't actually the right answer.
 
If there is a green conductor in the cord then imo it is unnecessary. I would just connect it to the pool deck box and be done with it.
 
TimB100000 said:
Thanks-- It's a Pentair Amerlite 12V/300W from around 2010. It definitely has a 3 wire cord (black, white,green) and the assembly instruction manual (which the customer still has, amazingly) is the same for both the 120V and 12V versions, and says to connect all three wires, which obviously makes sense for a 120V light. The manual doesn't say anything about whether the ground should be eventually connected to the grounding bar at the transformer. I'm still questioning what function a mains ground has on a 12V isolated circuit, and the safety when that (useless) mains ground connection might create a current path out the pool from a fault somewhere else in the residence. Seems like a case where more-grounding-is-better isn't actually the right answer.
Click to expand...

I just checked Pentair's site on this light. It is discontinued. Is it by chance LED?
There are 2 different manuals.
The Amerlite manual shows specific wiring as you stated.
The LED model does not.
Here's both manuals
 

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TimB100000 said:
It is definitely a 12V incandescent. Thank you for your responses on this.
Click to expand...

So did you end up grounding the light, or capping and leaving off the ground in the light's junction box? I am also confused as to why my LED 12v/35w has a ground wire and wonder what would happen with a ground fault elsewhere in the property. Electrical professionals seems to be divided by this question.
 
Please refer to 680.23(B)(2) and 680.23(F)(2). The verbage is “ other than listed low voltage luminares not requiring grounding “. If the manufacturer has listed this light with an EGC termination , you are required to ground it. Further more if the forming shell has been terminated with a non metallic conduit, and has provisions on the outside and inside of it, bonding should occur at these two points per 680.23(B)(2)(b) , 680.26(B)(5). and 680.6.
 
Greentagger said:
Please refer to 680.23(B)(2) and 680.23(F)(2). The verbage is “ other than listed low voltage luminares not requiring grounding “. If the manufacturer has listed this light with an EGC termination , you are required to ground it. Further more if the forming shell has been terminated with a non metallic conduit, and has provisions on the outside and inside of it, bonding should occur at these two points per 680.23(B)(2)(b) , 680.26(B)(5). and 680.6.
Click to expand...

Thank you! Yes I was planning to connect the light's ground wire (included in its cord) to one of the four grounding bolts in the metallic deck box. The niche is metallic, there is a bare bond wire coming into the deck box, and the forming shell's conduit is metallic terminating at the metallic deck box.

The other question I have, should the deck box ground back to the transformer ground terminals? I ask because the former 120V light was wired this way, and I will be using that existing 12AWG wire from the the deck box back to the transformer to supply the 12V, so I have a ground wire available there. The difference here obviously being the 12V output on the transformer does not inform a ground is necessary and according to the Pentair Amerilite instructions (updated October 2014 and available on their website), there is no ground wire shown from the deck box to the 12V transformer, so I had planned to cap that wire on both ends, leaving it totally disconnected. The branch circuit supplying the 120V feed from a GFCI receptacle to the transformer will of course be grounded to the transformer's ground bus.
 
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