Working non-union in the Bronx, mostly apartment renovations in prewar buildings. Today we were replacing a hallway fixture in a unit in Kingsbridge. Both 3-way switches off, and I checked the fixture with my non-contact tester anyway and it lit up on both wires. My mechanic checked with a meter, said there was voltage to ground on both conductors, then said "it's a Carter, leave it and call the office."
I have never heard of a Carter system. We did 3-ways at Apex and none of this matched. What is it, and why would both wires be hot with the light off? Appreciate any explanation.
edit: nobody touched anything live. He made us stop and the office is sending someone to look at it.
Electrical inspector (former contractor) · 26 years · Ocean County, NJ
Mentor✓ Accepted answer
Good catch testing a fixture you'd been told was off. That's the whole lesson. A Carter system is an old way of wiring 3-ways where the travelers carry the hot and the neutral, so with the light off both sides can be hot. I inspect in Jersey, not the city, so I won't speak to the NYC code, but I've seen a couple of these in very old houses at the shore. The answer is the same: rewire it properly, don't patch it.
Foreman, Inside Wireman (IBEW) · 19 years · Morris County, NJ
Mentor
This is why we test before we touch on every job, even when somebody swears it's off. Verify with a meter you've just checked on a known live source. Stay safe.