Pool lighting

[lshaff01]

My pool lights are driven by a 12 volt transformer. I notice that the 12 volt output was left “floating” i.e. the 0 volt tap was not connected to the AC neutral. My electrical training says it is bad practice to leave a transformer outputs “floating” and not referenced to anything. I was trained to connect the low side of the transformer to AC neutral so all voltages are referenced to the same thing. Without this connection, the transformer output is undefined and I suppose could be anything when referenced to AC neutral and earth ground (green wire). Question: (1) in pool applications, is it correct practice to leave the 0 volt tap of a transformer not connected to AC neutral? (2) Does the National Electrical code say anything about this? Thanks
P:S. Also I contacted the transformer manufacturer and he said “we refer all such questions to local codes and practice”. I also talked to a local electrical city inspector and he said “That’s a hell of a question”!

 

[suemarkp]

NE 680.23(A)(2) Transformers and Power Supplies. Transformers and power supplies used for the supply of underwater luminaires,
together with the transformer or power supply enclosure, shall be listed for swimming pool and spa use. The transformer or power supply shall incorporate either a transformer of the isolated winding type, with an ungrounded secondary that has a grounded metal barrier between
the primary and secondary windings, or one that incorporates an approved system of double insulation between the primary and secondary windings.

Ungrounded systems can be safer as it takes two faults to create a shock hazard. Systems need not be connected to the earth to establish their voltage. An ungrounded system's voltage with respect to the earth could be the same as a coat hanger hanging in the closet... The metal in the ungrounded system could couple lightning or other electric fields and have a voltage with respect to the earth, but pool light wires are typically short and buried.

 

[lshaff01]

Mark, thank you for your reply. You ,mentioned “two faults to create a shock hazard”. Could you elaborate on what these faults might be. Thanks

 

[suemarkp]

The first one would be one side of the circuit touching a metal enclosure. This basically creates a grounded system if that enclosure is grounded or makes good contact with the earth. Then you need the other side of the circuit to energize something else, like some isolated metal you touch or pool water. If it touched the same metal as the first fault, it would either burn up or trip some overcurrent device.

 

[GoldDigger]

One fault inside the transformer could elevate the whole circuit with respect to ground.
A second fault from anywhere in the secondary side could then expose that voltage on ungrounded metal.
This is the reason the grounded metal shield or double insulation are required in the transformer.
Two faults on the secondary side can only expose you to a 12V shock hazard (which might still be significant if you are immersed in water.).

Sent from my Pixel 4a using Tapatalk

 

[Buck Parrish]

My pool lights are driven by a 12 volt transformer. I notice that the 12 volt output was left “floating” i.e. the 0 volt tap was not connected to the AC neutral. My electrical training says it is bad practice to leave a transformer outputs “floating” and not referenced to anything. I was trained to connect the low side of the transformer to AC neutral so all voltages are referenced to the same thing. Without this connection, the transformer output is undefined and I suppose could be anything when referenced to AC neutral and earth ground (green wire). Question: (1) in pool applications, is it correct practice to leave the 0 volt tap of a transformer not connected to AC neutral? (2) Does the National Electrical code say anything about this? Thanks
P:S. Also I contacted the transformer manufacturer and he said “we refer all such questions to local codes and practice”. I also talked to a local electrical city inspector and he said “That’s a hell of a question”!

I'm an electrician, so I don't use the words an engineer might use , BUT - When it comes to pools the AC neutral is the one that can be deadly. As when the utilities neutral is lost. What ever is connected on the load side is searching a way back to the source.

 

[retirede]

Post #2 highlights the requirement for isolated windings in a pool lighting transformer.

Making a physical connection between the secondary winding and the source neutral (which was the original question) runs contrary to the isolation requirement.

 

[lshaff01]

First of all I would like to thank all of you for your responses. Very interesting reading. Just thought I would share my thoughts. I believe (1) With the transformer output floating, a short between the 120 volt primary and the 12 volt tap would allow the 12 volt side to float at 120 volts and the 0 volt tap to float at 120 V – 12 V = 108 volts. (2) With the transformer output floating, a short between the 120 volt primary and the 0 volt tap would allow the 12 volt side to float at 120 V +12 V = 132 volts and the 0 volt tap to float at 120 V. I may be wrong since I’ve never tried this but I would think this would be a disaster waiting to happen because I believe, the 12 volt circuits would operate as normal with no indication of a problem. With the 0 volt tap connected to AC neutral a short between 120 volts and the 12 volt tap or the 0 volt tap would destroy the 12 volt lights and probably destroy the transformer and cause the circuit breaker to trip. Certainly a rather dramatic an indication of a problem. But I accept you guys as the experts and will accept your wise council. I will leave my transformer as is. Again thank you very much for your thoughts.

 

[suemarkp]

Are any of the 12V lighting leads in contact with water? Usually, these pool lights are all sealed plastic and glass and everything is protected from corrosive pool water. So even if one side of the light is now 120V with respect to earth, it shouldn't matter as you can't touch it.

A short isn't supposed to happen with a pool transformer because of the double insulation or the grounded barrier between the windings. Pool lighting circuits over 15VAC need GFCI protection which would be a secondary safety mechanism. You can GFCI the lighting branch circuit for under 15V if you wish, but code doesn't require it unless the lighting transformer plugs into a receptacle instead of being hard wired - just about all pool area receptacles need to have GFCI protection.

 

[retirede]

First of all I would like to thank all of you for your responses. Very interesting reading. Just thought I would share my thoughts. I believe (1) With the transformer output floating, a short between the 120 volt primary and the 12 volt tap would allow the 12 volt side to float at 120 volts and the 0 volt tap to float at 120 V – 12 V = 108 volts. (2) With the transformer output floating, a short between the 120 volt primary and the 0 volt tap would allow the 12 volt side to float at 120 V +12 V = 132 volts and the 0 volt tap to float at 120 V. I may be wrong since I’ve never tried this but I would think this would be a disaster waiting to happen because I believe, the 12 volt circuits would operate as normal with no indication of a problem. With the 0 volt tap connected to AC neutral a short between 120 volts and the 12 volt tap or the 0 volt tap would destroy the 12 volt lights and probably destroy the transformer and cause the circuit breaker to trip. Certainly a rather dramatic an indication of a problem. But I accept you guys as the experts and will accept your wise council. I will leave my transformer as is. Again thank you very much for your thoughts.

A UL listed pool isolation transformer is designed to virtually eliminate the possibility of a failure that would cause contact between the primary and secondary.
I’ve never seen a documented case of an isolation failure of a pool transformer. I’ll admit, I haven’t extensively searched.