The Danger of Salience

Salience is part of how our brains prioritize information, but it can trick one into some amazing feats of logic.

For example, I was recently working in a control panel, troubleshooting a valve that didn't have power. Well, wouldn't you know it? Someone had turned off the breaker for the valve in the panel. This conveniently also explained the lack of position indication for the valve, because they were all on the same circuit.

When I powered up the valve, the circuit breaker immediately tripped, and the UPS for the I/O rack turned on, complaining that power was gone. Well, that was weird. It was a totally different circuit.....something must have shorted to ground, and was shorting out all the power. I turned off all of my load breakers, and everything looked normal. However, as soon as I turned on a single load, no matter how small, it wouldn't work. I pulled out the voltmeter: suddenly, neutral in the panel was reading very close to hot (118VAC). How had a blown circuit breaker caused such weird behavior? What was going on?

I followed this rabbit trail for 3.5 hours, wondering what was going wrong with my panel. The more loads I turned on in my panel, the worse the overvoltage in other circuits connected to the same lighting panel became. How could a shorted breaker do this?

Well, the answer was simple: the breaker had nothing to do with the problem. The problem was out on the utility pole, where the wind was whipping at 30mph. It pulled the neutral conductor free from the transformer.

Salience had gotten the better of me. My brain was so focused on the BREAKER causing the problem, it had kicked out the windstorm as a possible source. The breaker had high salience in my mind, but the ever present winds of Pocatello, Idaho had been reduced to background noise.