Spent 6 hours chasing a false alarm because of a bad ground connection

Got a call about a system in an old building downtown that kept tripping the fire zone. I checked every smoke detector and heat sensor first, all fine. Finally found the issue was a ground wire that had come loose inside the main panel, causing random voltage spikes. It took me from 10 AM until 4 PM to trace it because I was looking at the field devices, not the panel wiring. Anyone else run into weird grounding problems in older commercial spaces?

3 comments

3 Comments

wadefoster25d ago

@alicea26 is right about stray voltage being a grounding issue. The knob and tube thing is a different problem entirely, usually about old insulation cracking and causing shorts. Stray voltage from bad grounds happens in buildings of any age, even new ones if someone messed up the panel bond. For OP, loose ground wires inside the panel causing voltage spikes is pretty common in older downtown spots. The steel frames in those buildings can also act like a giant ground plane and mask where the trouble is. Next time, start at the panel and work outward whenever a zone is acting up with no clear cause. That saves you the headache of spending all day on field devices that are fine. I had a similar false alarm last year that turned out to be a ground screw that backed out from vibration near an elevator shaft.

elizabeth_martin2mo ago

Old building downtown" makes me think of that article about stray voltage in historic wiring.

alicea262mo ago

Wait, are you mixing up stray voltage with knob and tube wiring? That old article was mostly about how old insulation breaks down. Stray voltage is more of a grounding issue, like from bad pipes or something. It can happen in any building, not just the super old ones. The wiring in those downtown places is a whole other can of worms.