2 CBs, same pole.

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ptonsparky

ptonsparky

Tom
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NE (9.06 miles @5.9 Degrees from Winged Horses)
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EC - retired
We installed a couple motors earlier this summer. Each had a 3 pole 60 amp cb ahead of its starter and fused disconnect. Replaced both of them today. The same pole on each failed. They were the only loads running from what I understand. Everything else works great;, as did the motors with new breakers. Hopefully just a fluke because the replacements would be from the same batch.
 
ptonsparky said:
We installed a couple motors earlier this summer. Each had a 3 pole 60 amp cb ahead of its starter and fused disconnect. Replaced both of them today. The same pole on each failed. They were the only loads running from what I understand. Everything else works great;, as did the motors with new breakers. Hopefully just a fluke because the replacements would be from the same batch.
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Are you refering to replacing the breakers contactors, overload relays? If so what is your opinion as to how they failed requiring them to be replaced?
 
ptonsparky said:
The same pole failed on both Cbs. Mfg defect is my only thought. They will go back under a warranty exchange.
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They probably will exchange them as it is easier for them to do. But they run the risk of having another fail until the cause is discovered
If it were myself I would be concerned with what is actually happening. It's not that I'm lookint to avoid a warranty replace buy it make my product look bad and I know I sold quality products Why would the same pole being going south?
The my concern would be that you are loosing spring the tension that holds the ontacts closed on that pole. As such the one thing that I would investigate it heating of that pole. I would also take a sniff at the breaker with the probability that somethong may have fried on the inside which may give you a hint. If I were still a breaker application engineer when I got it back I would take the cove off and look. My goal is to resolve your problem in as short of time as possible to work with you in doing so.
I am to understand that its a 60a breaker. Is it cable in, cable out? Is it a breaker or an MCP that is part of a combination starter? Either way check the line connection and inspect it for heating. If so that heat can conduct itself into the stationary contact up through the moving contact and weaken the contact spring such that it looses its tension. That contact them will fail.
Are you sure that you really did have a contact failure? There are other oarts of the circuit for lone to load end that could fail but it would be highly unusual to have 2 failure in a row.
If it is an MCP there is a coil inside that is part of the magnetic pick up element. There have been times when the brazing of the conductors that connect to the coil failed causing an open circuit.
But again I would find it very unusual to have 2 breakers failknowing enough about breakers as I do.
 
I agree. Very odd they both fail at about the same time and same way. They are plug in breakers. CH330 to be exact. One feeds a 10 hp on small conveyor. Less than FLA. The other a centrifugal fan. Not sure of hp but it is a hard starting high efficiency. Both motors have starters & disconnects @ the motor location.
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The pole that failed on the conveyor looked slightly discolored, judgment call, but the buss tab is good. These breakers were opposite each other in the loadcenter.

If you were to align the breakers so both buss stabs were to the left and phase ABC top to bottom, the C phase is the one that failed open on both breakers.

Current on the feeders is close enough for government work. VD to load center is about 7 volts @ 75 amps. 240v hi leg delta with all fans and the one belt running. Closed delta IIRC.
 
Interesting. You have to make it difficult. But if it were easy anybody could do it.

The discoloration of the 'C' phase stab of one of the breakers would lead my to believe that there is heating at that point and those 3/4" per pole breakers probably aren't as forgiving. And if there is no discoloration on the bus stab may mean that there is enough mass as to dissipate the heat. I'm just trying to think outside the box here.
I am inclined to think that any heating that was enough to cause discoloration may be enough to weaken the moving contact spring causing a loss of contact pressure which results in poor contact pressure.
But, on the other hand, should the heating have originated from the contact itself that would lead one to believe that the decolorating was caused by a contact issue which would be unusual but certainly canted be ruled out. As such it could be a warranty issue. But that would be so unusual yet it can't be ruled out.
Being that you had a failure on a second breaker in the same way but that breaker showed no signs of heating may indicate a contact failure but did not generate enough heating for discoloration to occur.
What I find interesting is the same 'C' pole failed on each breaker and if I am to understand you correctly each breaker shared the some bus stab if that stab represented the 'C' phase.
There have been some very rare occasions that there has been just enough current to cause the breaker start to open and the contacts to float. It may sound strange taking just the right level of current but it has been known to cause contact failure.

Check the date codes on the breaker. If they are the same there could be a manufacturing issue. What would be of a concern is if you ended up with an additional failure and had to reconsider the cause of failure not being the breaker itself. But it is of my opinion that unless you can identify any more points that I have suggested you have not provided enough evidence that it is something other than a warranty issue at this point.
 
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