Jeremy Hargus
Member
- Location
- Schiller Park, Illinois
Ok let me try and get all the proper information in my first post.
I have a 225a square D breaker tripping the second I press the start button on a 125hp rotary screw compressor. I had this issue with this same machine at installation. Customer replaced the breaker with a new one, and it worked properly for 1000 hours give or take a few. Here is the kicker. Now it started tripping at startup again, but for three consecutive start attempts the breaker will trip instantly as the starter closes. Motor never even starts to turn, but on the fourth attempt it will start 95% of the time this is what will get it started. The breaker reset and restart attempts have to be right away though because any delay in trying it again will start he three count over again. The motor never actually starts to turn. Now for the details.
I can easily rotate the motor by hand.
Inrush on the breaker is currently maxed at 2250.
125hp motor.
I get 480 volts from L1 to L2, 479 volts from L2 to L3, and 478 from L1 to L3.
When unit is running I read 159, 159, 154 amps, and voltage on all phases drops only about 1 volt. The amp readings are almost ten above nameplate of the motor.
The equipment is only 40 feet from breaker, and has a disconnect on the wall outside of the unit.
The motor has no shorts to ground from any of the windings, and reading between 1.8 and 2.0 ohms on each winding when isolated from each other . (Didn't have a megohmeter with me)
With the motor removed front the starter it opens and closes perfectly with no tripping of the breaker. All connections are right, and no signs of heat damage of any sort.
The he only issue I can find (and it's a big one) is the wire size. The wire is printed as 3awg, but very hard to read, and my calculations show I should be using 4/0. Is that my issue? I would imagine the wire would handle the inrush, but burn up over time from excessive heat. I didn't install the electrical and the contractor is going to replace it with the proper size, but would that wire size difference cause an inrush trip of that breaker? And is a 225a breaker big enough? I was originally thinking it was another bad breaker but that just doesn't seem right to have two in a row
I have a 225a square D breaker tripping the second I press the start button on a 125hp rotary screw compressor. I had this issue with this same machine at installation. Customer replaced the breaker with a new one, and it worked properly for 1000 hours give or take a few. Here is the kicker. Now it started tripping at startup again, but for three consecutive start attempts the breaker will trip instantly as the starter closes. Motor never even starts to turn, but on the fourth attempt it will start 95% of the time this is what will get it started. The breaker reset and restart attempts have to be right away though because any delay in trying it again will start he three count over again. The motor never actually starts to turn. Now for the details.
I can easily rotate the motor by hand.
Inrush on the breaker is currently maxed at 2250.
125hp motor.
I get 480 volts from L1 to L2, 479 volts from L2 to L3, and 478 from L1 to L3.
When unit is running I read 159, 159, 154 amps, and voltage on all phases drops only about 1 volt. The amp readings are almost ten above nameplate of the motor.
The equipment is only 40 feet from breaker, and has a disconnect on the wall outside of the unit.
The motor has no shorts to ground from any of the windings, and reading between 1.8 and 2.0 ohms on each winding when isolated from each other . (Didn't have a megohmeter with me)
With the motor removed front the starter it opens and closes perfectly with no tripping of the breaker. All connections are right, and no signs of heat damage of any sort.
The he only issue I can find (and it's a big one) is the wire size. The wire is printed as 3awg, but very hard to read, and my calculations show I should be using 4/0. Is that my issue? I would imagine the wire would handle the inrush, but burn up over time from excessive heat. I didn't install the electrical and the contractor is going to replace it with the proper size, but would that wire size difference cause an inrush trip of that breaker? And is a 225a breaker big enough? I was originally thinking it was another bad breaker but that just doesn't seem right to have two in a row