Honey, I blew up the disco

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Coppersmith

Coppersmith

Senior Member
Location
Tampa, FL, USA
Occupation
Electrical Contractor
A client has a dead short in their A/C compressor. The disco blew up but the breaker in the old-style Sylvania panel did not trip. I strongly suggested to the client that this indicates a problem with the breaker(s) in the panel and a panel change should be done. I suppose an alternate theory is the switch in the disco was loose, but I rarely see QO style breakers/switches being loose. And I think the breaker should have tripped anyway. Is my conclusion correct?
 

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My money would be on the loose breaker (disconnect)...
Unless and until there was a fault phase to phase or phase to ground the supply breaker would have no reason to trip.
The supply breaker has no way of detecting a melt down in the disconnect until it faults.
 
ptonsparky said:
Loose breaker. I’ve seen QOs burn a hole right thru the back of the panel. Looked like someone had used a cutting torch. 120/240 that had been on the side of a grain bin. My thoughts then were long time vibration caused by the aeration fans.
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I agree. I have seen undertorqued lugs do the same thing.
 
Yes, even the infamous Square D QO stuff has its faults like any other brand. I’ve seen loose fitting buss stab connections in the QO line before.
 
mopowr steve said:
Yes, even the infamous Square D QO stuff has its faults like any other brand. I’ve seen loose fitting buss stab connections in the QO line before.
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Especially when the breakers have been uninstalled and reinstalled. I seem to recall that some plug-on joint compound is suggested when a breaker is reinstalled. It has been along time, if ever, since I read a QO instruction sheet.
 
After I de-termed the wires and removed the disco from the wall, I decided I had better verify there was no short or open in any part of the circuit before installing a new disco. The cable going back to the panel was good both powered off and on. When I tested the leads going into the compressor I found a dead short from one hot lead to ground. I opened the compressor and verified the whip was not the culprit, the compressor itself had a short.

The A/C service guy was there the day before. (He referred me to the HO). He must have taken one look at the disco and decided that was the problem and not done any tests on his own equipment. I called the A/C company to inform them and they scheduled another service call to actually fix the unit.
 
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"disco"

"disco"

I lived through the 1970s. I do a double-take every time I see that abbreviation.

night-fever1.jpg
 
drcampbell said:
I lived through the 1970s. I do a double-take every time I see that abbreviation.
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And I think about the discotheque kind whenever I say it.

In the 70's my mom managed one of the hottest discos in NYC. There was always a long velvet rope line of people waiting for their turn to convince the bouncer to let them in. The cover was $35 each. I took dates there. We would have the taxi pull right up to the door. I would whisper in the bouncer's ear "my mom put me on the list" and he would let us right in with everyone in line straining to see who we were. One of the coolest experiences I've ever had.

Oh, and I still love disco music. I sometimes listen to it while working.

https://www.youtube.com/watch?v=zue7wsi_xeo
 
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Coppersmith said:
A client has a dead short in their A/C compressor. The disco blew up but the breaker in the old-style Sylvania panel did not trip. I strongly suggested to the client that this indicates a problem with the breaker(s) in the panel and a panel change should be done. I suppose an alternate theory is the switch in the disco was loose, but I rarely see QO style breakers/switches being loose. And I think the breaker should have tripped anyway. Is my conclusion correct?
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what are the voltages involved
 
romex jockey said:
What's interesting is a thermal-magnetic device took on so much......thermal....~RJ~:cool:
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Turns out this was just a switch and not a breaker, but I have seen that happen to breakers many times without tripping the breaker, not just QO breakers either. But that thermal energy was more focused on the lug or bus connector and not on the thermal trip component, so it all depends on where thermal transfer ends up going to determine how the thermal trip will respond to it.
 
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