I'm replacing a 240-volt split-phase electric baseboard heater. I've shut the power off at both the thermostat and the breaker box. Testing the wires with a non-contact voltage tester shows an intermittent "live" indication on the non-switched wire; it shows a continuous "live" indication on the hot side of a nearby outlet. Testing the wires with a multimeter shows 0V for switched-to-non-switched, switched-to-ground, and non-switched to ground; it shows 120V for hot-to-neutral and hot-to-ground in a nearby outlet.
Which should I believe? Is the NCV picking up a residual signal from the nearby outlet, or is the multimeter somehow ignoring the high-voltage wires?
Best Answer
Trust the multimeter. No-contact testers should only be used for a preliminary test. If the no-contact indicates power a regular voltage tester or DMM should be used to verify.
A no-contact tester is susceptible to induced currents from wiring running in the same conduit or in close proximity to the wiring being tested.
Safety first though. Make sure circuits are de-energized before working in them.