multimeter
New User
- Location
- US
- Occupation
- Renovator
This is more an FYI but I recently observed stray voltage where I never expected to see it (US code).
I have installed a new subpanel in my garage which I am using to feed a few different circuits: EV, welder and a couple of 120V/240V 20A circuits with outlets. To save hassle, I wired the 120V/240V circuits with 4-wire Romex, and just picked off the conductors I need for each outlet (everything is pigtailed). The circuits are protected with 2P GFCI breakers.
Now, perhaps this is bad practice, but until I get the new 100A feed installed, I have temporarily powered one side of the panel (black) with a 120V pre-existing lighting circuit (14 gauge). This is to feed a couple of new garage door openers and some 120V outlets. I am the only one working on this so I know not to hook up anything too chunky. And it will blow the circuit breaker for the lighting circuit in the main panel if I did anyway, so I figured as a temporary measure not really a safety issue.
This where it gets interesting. I was wiring a 240V outlet in one of the circuits and noticed a tingle in the non-powered leg (red). Breaker was off of course. So I got out my multimeter and measured the voltage at the breaker terminals. Sure enough, the red leg was reading 63V (essentially 120V/2). Only when I turned off the second breaker, which was only powered and only had load on the other (black) leg, did the voltage on the red leg of the circuit I was working on drop to zero.
I am guessing that when using a 2P GFCI breaker (Square D Homeline at least), and powering and loading only one leg, there's some inductive process that generates 1/2 the voltage on the other leg, and that gets passed back through the panel bus. Presumably not enough to carry any significant current, but still a little scary when you feel that 63V on a circuit that is not only disconnected at the breaker, but also unpowered at the panel bus!
I have installed a new subpanel in my garage which I am using to feed a few different circuits: EV, welder and a couple of 120V/240V 20A circuits with outlets. To save hassle, I wired the 120V/240V circuits with 4-wire Romex, and just picked off the conductors I need for each outlet (everything is pigtailed). The circuits are protected with 2P GFCI breakers.
Now, perhaps this is bad practice, but until I get the new 100A feed installed, I have temporarily powered one side of the panel (black) with a 120V pre-existing lighting circuit (14 gauge). This is to feed a couple of new garage door openers and some 120V outlets. I am the only one working on this so I know not to hook up anything too chunky. And it will blow the circuit breaker for the lighting circuit in the main panel if I did anyway, so I figured as a temporary measure not really a safety issue.
This where it gets interesting. I was wiring a 240V outlet in one of the circuits and noticed a tingle in the non-powered leg (red). Breaker was off of course. So I got out my multimeter and measured the voltage at the breaker terminals. Sure enough, the red leg was reading 63V (essentially 120V/2). Only when I turned off the second breaker, which was only powered and only had load on the other (black) leg, did the voltage on the red leg of the circuit I was working on drop to zero.
I am guessing that when using a 2P GFCI breaker (Square D Homeline at least), and powering and loading only one leg, there's some inductive process that generates 1/2 the voltage on the other leg, and that gets passed back through the panel bus. Presumably not enough to carry any significant current, but still a little scary when you feel that 63V on a circuit that is not only disconnected at the breaker, but also unpowered at the panel bus!
