Motor starter failure

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bigsteve80

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Helena, AR
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Chemical Engineer
We have a 50 HP vacuum pump that had the starter fail the other day; it looks like one of the contact bars failed and arced across (this starter was about 25 years old). This shot a fireball out of the starter that nearly hit the operator. Since it wasn't arcing to ground or phase-to-phase, it never tripped the circuit breaker. We replaced the starter and it's running fine now... However, we're doing our incident report, and since someone could have gotten seriously hurt, we need to have a recommended corrective action. I can't think of something that would definitely prevent this from happening in the future. Is there a recommended maximum age for contactors? I can't find anything in NEC or NFPA 70B.
 
bigsteve80 said:
... Since it wasn't arcing to ground or phase-to-phase, it never tripped the circuit breaker. We replaced the starter and it's running fine now... However, we're doing our incident report, and since someone could have gotten seriously hurt, we need to have a recommended corrective action. I can't think of something that would definitely prevent this from happening in the future.
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bigsteve80 said:
They had opened thinking that the thermal overload had tripped.
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retirede said:
The corrective action is to never open a live enclosure without PPE.
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Especially since there was a known problem, shutting off the circuit breaker before opening the enclosure would be an appropriate rule to follow.
And as retirede posted, PPE should be required if the breaker has to be left on.
 
Where exactly did the fireball come from? If the starter contactor had the arch shields on it, I would not expect a fire ball to come out without a short of some sort. Did the fuses blow before the circuit breaker could open?
 
I learned to stand off to the side of operating with door open
Starter life? I have seen AB 509 starters last for 50 years, where the motor starts and runs for many hours
Recommended action? PM on the starter. NEMA starters are simple to inspect the contacts on
If it was an IEC starter, they are not as robust and repairable as a NEMA.
 
bigsteve80 said:
... Since it wasn't arcing to ground or phase-to-phase, it never tripped the circuit breaker. …
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Just so you know, a breaker or fuse would NOT have prevented that fireball, hence the requirement for PPE.

There is no maximum lifespan of NEMA contactors, but that does not mean you don’t periodically check it for wear and tear and the need for repair or replacement. IEC contactors are designed to last 1 million operations, then you throw them away. That’s once every 10 minutes for 20 years.
 
ptonsparky said:
I don't know about age, but an enclosure should have contained a fireball.
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This is not always the case. Almost no electrical equipment is tested for internal arcing. You cannot depend on a closed door for protection from arcing faults unless the equipment is arc-rated (not common). There are numerous cases where doors were blown off completely. A closed door will provide some protection, but won't necessarily prevent burn injuries.
 
Did anyone check the specifics such as the starter withstand rating, available short-circuit amps, etc.
Current limiting fuses vs the breaker might provide improved protection.
 
David Castor said:
This is not always the case. Almost no electrical equipment is tested for internal arcing. You cannot depend on a closed door for protection from arcing faults unless the equipment is arc-rated (not common). There are numerous cases where doors were blown off completely. A closed door will provide some protection, but won't necessarily prevent burn injuries.
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First line of defense is still keep the cover on!
 
bigsteve80 said:
I can't think of something that would definitely prevent this from happening in the future. Is there a recommended maximum age for contactors? I can't find anything in NEC or NFPA 70B.
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From the description of the failure it appears the starter experienced an high resistance connection that went undetected. A high resistance connection will not trip an overcurrent protection device. The heat generated causes an insulation failure and usually a fault. An EPM will normally pick up these type of impending failures.

There is nothing in the NEC or NFPA 70B that puts a maximum age on electrical equipment. Electrical equipment doesn't last forever. Life expectancy of electrical equipment is based on several factors:

1. Use
2. Operating Conditions
3. Maintenance.
4. Physical Abuse
5. Electrical anomaly or fault events.

Older equipment is more like to experience a failure if it isn't properly maintained. You didn't note what or if there was an EPM in place as recommended by NFPA 70B.

There are recommendations about the life expectancy of electrical equipment A properly maintained starter in favorable operating conditions and not subject to electrical anomalies or faults should provide up to 30 years of reliable service from the information I have researched. There is no specific number of years for life expectancy.
 
bigsteve80 said:
We have a 50 HP vacuum pump that had the starter fail the other day; it looks like one of the contact bars failed and arced across (this starter was about 25 years old). This shot a fireball out of the starter that nearly hit the operator. Since it wasn't arcing to ground or phase-to-phase, it never tripped the circuit breaker. We replaced the starter and it's running fine now... However, we're doing our incident report, and since someone could have gotten seriously hurt, we need to have a recommended corrective action. I can't think of something that would definitely prevent this from happening in the future. Is there a recommended maximum age for contactors? I can't find anything in NEC or NFPA 70B.
Click to expand...
The large hospital that I retired from had a strict PM schedule for all drives, starters, & panels . From once to four times a year we had to take voltage drop measurements between the line & load side of starters and overload blocks while running. We also performed IR scans and often found one set of contacts on a starter was several times higher then the others so we had to LOTO starter remove cover and inspect contacts and replace them if needed. Unfortunately more & more equipment are supplied with inferior IEC starters that covers can not be removed. Was shocked when I came across an IEC junk contactor on a 100HP Fire pump that you could not remove cover to inspect contacts. If you have a piece of equipment that starts & stops a lot would spend the extra money and purchase a made in USA full size starter such as Allen Bradley or Square D. At one company we had over 30 chocolate tanks where the energy management system turned 5 to 10 HP motors on & off every 15 minutes 24/7 that had 40 year old Allen Bradley starters. Maybe twice a year would have to replace the contacts or coil. Never blow up or fired out sparks. Get what you pay for. We had a lot of problems with crap IEC starters on pit pumps that started & stopped every few minutes. Was lucky to get a year out of IEC stuff. Did not have room in control panels to go with full size starters but used 25 HP starters for 10 HP motors and they lasted a good amount of time.
 
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