Shoutout to the old-timer who showed me a trick with a solenoid

I was troubleshooting a stubborn 24V control circuit on a boiler last week and kept getting ghost voltage readings. He had me check across the coil with the solenoid actually energized, and the reading dropped to near zero, proving the coil was good but the wiring run was picking up induction. Anyone have a go-to method for chasing down induced voltage on low voltage control lines?

3 comments

3 Comments

wendysanchez20d ago

Honestly, that old school trick seems like a waste of time to me. Why not just use a proper solenoid tester from the start instead of messing with a multimeter on a live circuit? Induced voltage is a known issue, so the real fix is just running shielded cable and grounding it right. Checking after the fact doesn't actually solve the problem you already have. Seems like patching a symptom instead of doing the job correctly the first time.

lunaf6719d ago

Oh man, that's a classic field fix right there. @lily70 is totally right about the test light trick, it's saved my butt more than once when my fancy meter was just confusing me. Sure, shielded cable is the textbook answer, but sometimes you just need to prove the solenoid works so you can get the heat back on now. You can argue about the perfect fix after the building is warm.

lily7020d ago

That old timer's trick is solid for a quick field check when you're up to your elbows in a machine. Shielded cable is the right fix for a new install, but you can't always rewire a 30 year old system on the spot. For chasing it down, a low impedance meter or even just a simple incandescent test light will load the circuit enough to make that ghost voltage disappear and show you the real problem.