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Blew a transformer on a Vista 20p panel last Tuesday
I was swapping out an old backup battery on a Vista 20p last week. Standard job, right? I got everything wired back up and hit the AC power. Then I heard this loud POP and smelled that burnt electronics smell. Turns out I accidentally shorted the AC terminals with my screwdriver while tightening the connections. Fried the transformer instantly. That was a 40 dollar part plus a trip back to the shop. I spent an extra hour rerunning the power because the original transformer was mounted in a tight spot and I had to replace the whole thing. Now I always use a non contact voltage tester on the wires before I touch anything. Has anyone else had a similar oops moment with panel power?
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paige_owens51mo ago
Man, that is rough. I get why you would check voltage after that. But here is something nobody brings up. Those old transformers on 20p panels sometimes have a slight crack in the plastic housing from age and heat. When you tighten the screw, it can push the cracked plastic just enough to let the metal terminal touch the metal box. That creates a direct short to ground, not just a cross between the AC wires. It pops the transformer way faster than a regular short. I have seen it happen twice on panels that were over 10 years old. The transformer looks fine from the outside but that tiny hidden crack is what gets you. So next time, wiggle the transformer base gently before you put power to it. If it feels loose or the plastic moves a little, just replace the whole transformer mount too. Saves the hassle.
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Wait, have you ever checked an old 20p transformer for hairline cracks before? My buddy Dave did this exact thing last fall, swore the transformer was fine but the plastic housing had this tiny split on the bottom side. He tightened the screw and it popped before he even flipped the breaker.
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