I got bitten by that bug early when I was a third-year electrical apprentice. I was in a large switchroom with half a dozen electricians and 4-5 engineers, trying to work out why a 3.3kV oil filled breaker had brought the fire brigade into the plant for the second time in a week.
With all of the brains trust poring over drawings and testing wiring, I all of a sudden noticed something.
"Hey...guys? This timer up here?"
"Yeah?"
"That was put in by [contractor] a few months back, right?"
"Yeah?"
"And it's job is to drop out the closing coil after 3 seconds if the breaker doesn't close, right?"
"Yes. The closing coil is temporary duty only. If it stays on for more than a few seconds it'll let all the smoke out."
(I look around at all the smoke lingering in the room)
"...I don't think it's wired right."
"No, it is, we've checked all that. And when the breaker closes, you can see the light on the timer come on very briefly - and then turn off a split second later when the limit switch confirms the breaker has closed."
"Yes, but...what control voltage are we running here?"
"48VDC"
"Yeah, see, the coil is wired to A1 and A2, and A1/A2 is labeled as 110-240VAC. There's another coil, B1/B2 labeled as 24-48V AC/DC".
"But it's working! The light comes on!"
"Give me a piece of bridge wire."
I bridge 48VDC to A1, and nothing. No light. We open and close the breaker and once again see that the light comes on very briefly.
"What the ****? How does it work with THAT 48VDC but not THAT 48VDC?"
We test again. Same results.
"Hang on guys. Open and close the breaker again. Let me watch very closely."
We open and close the breaker.
"Okay, I see what's going on here. The light on the timer doesn't come on when the closing coil comes on. When you press the close button, that big f*** off contactor there comes in. The one that's so old it has an open frame and an asbestos arc shield."
"Yes, that brings in the closing coil."
"Yep. And then when the limit switch says the breaker is closed, the contactor drops out and drops out the closing coil."
"Yes."
"The light on the timer doesn't come on until that contactor drops out. I think the inductive kick from magnetic field on that big f***-off contactor coil opening is causing the voltage to rise just high enough for the timer to operate on the 110-240V AC/DC setting. Just for a split second, and then it turns off. But all of this is only happening after we get confirmation that the breaker has closed, and drop out the coil."
"..."
"Disconnect the limit switch feedback, and the closing coil so we don't set fire to it again, and press the close button. I bet that timer won't come on until we drop out the closing coil manually."
Sure enough, every timer in that whole switchroom was wired wrong and never worked. They just looked like they worked because of the ancient contactor and the collapsing magnetic field.
As an apprentice, it felt pretty good to work that out in front of the whole crowd of tradespeople and engineers.
More recently, I put in a new SCADA system on a site that had never previously had SCADA. There was a moment of quiet pride when I overheard two of the site engineers/supervisors saying to each other "gee, this new SCADA makes the rest of the site look like ****, doesn't it!"
