Compressor Starter Box Wiring

4x4dually said:
If both legs of a single phase motor aren't pulling the same amount of amps...then there is something wrong. LOL It "is" possible. For instance, if a winding starts shorting or some oddball crap, so it is advised to run both thermal overloads. We were merely stating that he could jumper it if he wanted to so he could get it running. On a three phase, you could protect two out of the three if you wanted....but no one in their right mind would do it that way. You wouldn't believe the amount of Nigerian rigged schidt that shows up while doing service calls. It always amazed me what people thought was ok.
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Protecting 2 of 3 legs was a common practice for years, overloads are for overloading conditions, fuses/MCP are protection for shorts. Also on a single phase motor if one of the coils starts shorting windings (short out to themselves) then the single overload will still protect, as the impedance of the motor is decreased and the current goes up in the whole circuit. I do agree, that running the 2nd overload won't hurt anything, but I don't see a real scenario, that the circuit isn't adequately protected.
 
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The winding can open up and the side from the jumper can be the one shorting to the case and it not be protected. There is ALWAYS a case for fukkery. ;)

Just put the correct heaters in all positions and don't question it. That's my policy. :D


Speaking of fukkery.....I started the little chinesium band saw on some tubing the other night. Then I turned and started working on a gate facing the other direction. The wife stepped out and said "um...honey...." The blade was locked and the motor was just a boiling out black smoke. Melted the motor to the ground. 20amp breaker never bobbled. Square D Homeline too, not that FPE red handled crap. It was an amazing show. :hehe: Now see, if I had a starter and heaters on it...that wouldn't have happened.
 
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4x4dually said:
The winding can open up and the side from the jumper can be the one shorting to the case and it not be protected. There is ALWAYS a case for fukkery. ;)

Just put the correct heaters in all positions and don't question it. That's my policy. :D


Speaking of fukkery.....I started the little chinesium band saw on some tubing the other night. Then I turned and started working on a gate facing the other direction. The wife stepped out and said "um...honey...." The blade was locked and the motor was just a boiling out black smoke. Melted the motor to the ground. 20amp breaker never bobbled. Square D Homeline too, not that FPE red handled crap. It was an amazing show. :hehe: Now see, if I had a starter and heaters on it...that wouldn't have happened.
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If the winding is shorted to the case, then it will pop the breaker. :) I am guessing your motor wasn't shorted to the case, LOL. So yes a properly sized overload would have protected it.

Overcurrent protection is to protect the downstream devices, if the motor has bad insulation, it is already bad LOL. Just keep the place from burning down when it shorts to the case! HAHA
 
zstroken said:
If the winding is shorted to the case, then it will pop the breaker. :) I am guessing your motor wasn't shorted to the case, LOL. So yes a properly sized overload would have protected it.

Overcurrent protection is to protect the downstream devices, if the motor has bad insulation, it is already bad LOL. Just keep the place from burning down when it shorts to the case! HAHA
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You realize you are preaching to the choir, correct? LOL


HEY OP! Did you get that air pump working yet or not?
 
Not yet Jory. One more week of travel and hotel living for me. Then I'll be home and have time to tinker.

I greatly appreciate the info! Will put this to use.

For the record, it's a 220v 5hp motor.

Nick
 
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Update.
Compressor works without starter box. I had a "doh!" moment when looking at my cousins IR compressor that is identical to mine.

He pointed out that his has start and run capacitors with a pressure switch rated to take the 15amp kick at first start up.

I get home, see that mine too has start and run capacitors. Cleaned the dirt off the pressure switch label, and read that it's also rated for 15amps. Wired that sucker direct to the switch and it fired off! I don't even care at this point how long it took to figure all this out. Just glad to finally have compressed air.

Jory, I printed out your schematic and placed it in the starter box. Might just need it one day. Thanks for the insight.
 
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