low voltage reading at junction box when pool light switch off

[DallasRick]

I disconnected the wires at my pool light j-box because the pvc conduit feeding the power bundle pulled away from the box and had filled with water (sits close to a sprinkler) and had left it like that for a while. I went to reconnect the wires to make sure the light itself was still working. Using a non-contact tester to be safe, I discovered that with the breaker on (home breaker, no automation equipment, just mechanical timer), and switch off, I was getting a low voltage tone. So, I got out the multimeter and got the following results:

With wires from switch disconnected from pool light wires (except ground)
-124v when the light switch is on.
-17v when the light switch is off.
-0v when the breaker is off.
-no readings from pool light wires as expected

With wires reconnected to pool light wires:
-124v light switch on
-0v light switch off

I'm trying to figure out what might produce a 17v reading with switch light off when wires are disconnected from the pool light wires, but no reading when connected, unless of course the switch is in on position. All wires feed through the spa light j-box on other side of yard where the GFCI outlet is located and I have not opened that j-box yet (because access is slightly difficult as it's sort of integrated into the fence) so I don't know if I'd get similar readings from the spa light wires, but the GFCI tests normal. The spa light doesn't work but I believe it died from old age and I haven't bothered to change it yet. The pool light (Intellibrite 5g multi-color) works. I'm not overly concerned at this point because everything has worked fine since I bought the house 10 years ago and it makes little sense to get normal volts when on, low volts when off. I'll probably get an electrician out but before I do am trying to determine what potential reasons could explain this, besides ghost voltage. Unfortunately, my multimeter doesn't have a LoZ setting so I can't eliminate that yet but wonder if anyone else has come across a similar issue and determined a cause.

 

[JohnT]

Welcome to TFP!

What wires are you measuring? Does the neutral pass through the switch box or does it go a different route?
Measuring from neutral to the hot going to the switch should always be nominally 120V unless the breaker is off.

Measuring from neutral to the wire going to the light with the switch off shouldn‘t show a real voltage. Could be an induced voltage in the wire running from switch to light.

 

[ajw22]

Welcome to TFP.

Where are you measuring voltage between?

I would replace the light switch. Is the light switch outdoors? I think the light switch has some corrosion passing voltage when the switch should be off.

 

[JamesW]

-17v when the light switch is off.

Check from the power wire to ground and from the neutral wire to ground.

 

[DallasRick]

Welcome to TFP!

What wires are you measuring? Does the neutral pass through the switch box or does it go a different route?
Measuring from neutral to the hot going to the switch should always be nominally 120V unless the breaker is off.

Measuring from neutral to the wire going to the light with the switch off shouldn‘t show a real voltage. Could be an induced voltage in the wire running from switch to light.

Yes, the more I dig the more I think it may just be induced or phantom voltage, but my experience with this stuff is limited to DIY necessities and I prefer to be overly cautious when it comes to electricity and pool water, but I accidentally discovered this phenomenon and know it could actually be nothing of concern and have never had an issue with the lights. Which is why I'm looking for a few answers before I bring in the big guns.

To answer your question, I'm measuring the hot and common going into the pool light j-box. It's a yellow hot wire and white common.

The switch box is on other side of pool nearer back door for convenience. 2 Romex from soffit/attic (house panel) fed through conduit down side of house into switch box. They pass by the switches (connected to like wires via wire nuts), exiting conduit at bottom of box going underground. Conduit leads to a 2-gang box that has a switch for the spa air pump and a GFCI outlet, as required. It also serves as j-box for spa light. In addition to the wires the Romex is connected to in the switch box, there are 3 additional wires coming from the bottom/exit side of the conduit. Red, orange and yellow wire.

The red wire is power coming back into the switch box and is push-connected to line side of spa switch, power. There is also a short black wire connected to that line screw, which jumps to the pool light switch line side push-connected to give it power. The bypass and return wires I assume are to accommodate getting the GFCI in the circuit between circuit breaker and switches.

The orange wire is push-connected to spa light switch load side.

The yellow wire is push-connected to pool light switch load side. This is the wire I am ultimately testing at the pool light j-box that gives me a 17v reading (at that j-box with the switch in off position), but I don't get that at the switch itself. At the switch I get 122v with breaker on, 0v when off.

The wire (at the j-box with switch in off position) can be touched with no hint of current despite the 17v reading. Again, when I reconnect it and the common to the pool light wire harness that reading goes to 0v, so seemingly normal. I think I'm just being haunted but want to be sure.

 

[DallasRick]

Welcome to TFP.

Where are you measuring voltage between?

I would replace the light switch. Is the light switch outdoors? I think the light switch has some corrosion passing voltage when the switch should be off.

I've measured at the switch and at the j-box. J-box is where the 17v measure happens. I did replace the switch to see if that was the issue but got the same readings.