Need some ideas on what may be happening. The new equipment and system is as follows: Three 480V 30hp fans, 6 awg wires are used each connected to a GECR306E1 starter and then connected to Eaton 80amp E125S breakers in a 400amp panel. The panel serves all 3phases loads including 3 elevators. The problem is fan #1 trips the breaker on start up randomly up to 50% of the time. The heaters in the starter have not tripped. There have been no issues with the other two fans. The fans stage on in 5-10 sec steps. So we thought it could be something to do with the order so that was changed and fan #1 breaker trips no matter the start order. The fan motor was replaced and the breaker continued to trip. The breaker was switched with a spare breaker. Breaker would still trip. Now for the really confusing part, all three fan breakers are on the right side of the panel starting at the top with Fan #1(problem circuit). If fan#1 wires are moved to fan #2 breaker (next breaker down) and #2 is moved to #1 breaker the problem goes away??. Any ideas?
Confusing breaker tripping problem
- Thread starter MEP_PM
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USMC1302
Senior Member
- Location
- NW Indiana
I'm sure there will be some sharp people along to help you shortly, but it sounds like you have tried some logical troubleshooting steps. It also sounds like you have isolated a possible problem to that one breaker location. Could the bussing be damaged/poor connection in that one location? Maybe forget that, you have switched wires on the breakers already.
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sbutler
Member
- Location
- North Charleston, SC
USMC, I would tend to agree with you but I would think the problem would have remained when the wiring was swapped if it was a breaker-bus connection issue. Could there have been a loose connection originally causing a high resistance connection and it went away when you swapped and reterminated? Did you try swapping back to the original line-up and re-try?
That's an excellent idea.
But if this still leaves you puzzled, I wouldn't get too hung up on the fact that it quit tripping when your swapped wires between the two breakers. That may just be due to slight differences in the exact trip points.
Some suggestions: Measure the running current of all the fans, and see if you can also catch the starting current. Measure voltages also, while running and starting if possible.
If that looks good, I wouldn't worry about the motor or the breaker - you've changed both and despite the fact that one breaker holds, at least 2 breakers are tripping on this circuit.
That leaves the fan itself, the circuit wiring, and the starter. The fan could have a bad bearing, or maybe a belt that is too tight? The wiring could have a bare spot on the isulation that might be making contact with the conduit when the wiring moves around due to the starting current. If the starter has a bad contact, it might be single phasing the motor on startup. I think any of these could trip a breaker.
Steve
swptln
Member
- Location
- East Brookfield, MA
I think Steve hit the problem, your trip points designed into the breakers are different.
This is why we can apply 430.52 and the according table to compensate for inrush start currents.
The breakers might have to be increased in size or you may end up with nuisance tripping due to start up currents.
Sounds to me like those breakers are border line for those motors.
This is why we can apply 430.52 and the according table to compensate for inrush start currents.
The breakers might have to be increased in size or you may end up with nuisance tripping due to start up currents.
Sounds to me like those breakers are border line for those motors.
stew
Senior Member
- Location
- federal way,washington
Sounds like a good time to pull out the old tried and true megger to eliminate or at least hopefully eliminate an intermittent grounding situation in a pipe on the branch side. Fault may show with 1000 vdc megger. if its actually a nicked wire etc. Check both to ground and between wires as well.
This may have been asked and I'm overlooking it.. do the breakers have a adjustable trip ?
In my experience fans can have some really long start currents and your 80 amp breakers are a bit lower than what is allowed for GF-SC protection. The one breaker trip curve might be slightly different and the air flow may be such that that one fan is requiring a longer time ramping.
NEC would allow a 100 amp breaker or even larger (see exceptions to 430,52)
In my experience fans can have some really long start currents and your 80 amp breakers are a bit lower than what is allowed for GF-SC protection. The one breaker trip curve might be slightly different and the air flow may be such that that one fan is requiring a longer time ramping.
NEC would allow a 100 amp breaker or even larger (see exceptions to 430,52)
USMC1302
Senior Member
- Location
- NW Indiana
The sharp guys are chiming in, but you said if you change the wires from breaker #2 to breaker #1, the problem goes away? Have you tried switching positions of those two breakers?
brian john
Senior Member
- Location
- Leesburg, VA
1. Possibly the CB instantaneous is bad? Requiring a CB replacement
2. The inrush current as noted may be taking the CB out.
3. Are the two CB?s identical?
4. Do they have adjustable instantaneous.
5. Have you measured the inrush currents?
6. These are identical fans, have you checked running current. Could be a mechanical issue resulting in higher inrush current, this mechanical issue could show up doing the run.
The issue is there you are just missing it.
2. The inrush current as noted may be taking the CB out.
3. Are the two CB?s identical?
4. Do they have adjustable instantaneous.
5. Have you measured the inrush currents?
6. These are identical fans, have you checked running current. Could be a mechanical issue resulting in higher inrush current, this mechanical issue could show up doing the run.
The issue is there you are just missing it.
kwired
Electron manager
- Location
- NE Nebraska
What about circuit length to Fan #1? If it is the shortest run of all the fans the instantaneous current at start up will be higher if all other conditions are equal. Shorter length = less impedance = higher starting current.
Not knowing what the fans are for, are these fans capable of "windmilling" or spinning backward when not running and have to first reverse the load before accelerating it in a forward direction? That could also add to problems.
Not knowing what the fans are for, are these fans capable of "windmilling" or spinning backward when not running and have to first reverse the load before accelerating it in a forward direction? That could also add to problems.
brian john
Senior Member
- Location
- Leesburg, VA
Good pull, forgot that. We have had that issue a few times.
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