Question about why my meter was off by 0.3 volts all week

I was chasing a weird voltage drop on a 120v circuit in a new build over in Franklin County last Wednesday. Checked my Fluke against the panel and it kept reading 119.2 when the main was showing 119.5. Then a journeyman walks up and tells me my leads were dirty from all the drywall dust on that job. Quick wipe with alcohol and it fixed the issue. That 0.3 volts doesn't sound like much in my experience, but when you're checking sensitive equipment or trying to pin down a tolerance issue it can mess with your head. How often do you guys clean your meter leads? I never gave it a thought until this week.

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clairebaker4mo ago

Read an article in EC&M a few months back about this. Dirty leads cause more headaches than people realize. The drywall dust is especially bad because it's conductive when it gets damp. Had a guy on a different forum tell me he was chasing a 0.5 volt ghost for two days. Turned out to be grime on his test probes. I keep a little alcohol wipe pack in my bag now after hearing that story. Cleaning them once a week is probably overkill but I do it anyway. Saves time and stops you from looking dumb in front of the journeyman.

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markc844mo ago

Man I used to think cleaning probes was just one of those old timer superstitions, but now I'm with you completely after reading that EC&M piece. I had a buddy who literally rebuilt a whole control board before realizing his meter was lying to him because of some corrosion on the tips. It's wild how such a small thing can waste hours and make you question your sanity.

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