Miniature ABB Breaker Failure

[Barrie66]

Hi All,
Has anyone had or heard of a miniature ABB 2 pole breaker failing?
I was in Mexico last week commissioning our equipment that has a number of ABB miniature breakers installed in the Control Cubicle.
On switching on the main 200A/480V disconnect, also in the control cubicle. There was a loud explosion caused by a flash over between terminals on the two incoming phases of a 3A ABB miniature breaker. The resultant carbon/copper etc. blew downwards and onto the terminals of a 3phase terminal block which caused a further short circuit on all three phases.
Luckily we have current 150A current limiting fuses in the disconnect so at least this limited the fault current. They in fact ruptured before the breaker at the substation tripped.
I should also say that while the humidity was high around 80% the whole cabinet and all equipment was very clean and no condensation was apparent anywhere.
We will have to renew both the 2 pole breaker and the terminal block as the blackening is extensive. As a result of this, I am a little wary of installing a new breaker, although we have used this type of breaker in many of our units previously.
Any previous experience or comments would be appreciated.

 

[waross]

I have reread this several times to see if I am making a mistake or misunderstanding something.
I keep coming back to the phrase

a flash over between terminals on the two incoming phases

It sounds as if the breaker was the victim rather than the perpetrator. I would suspect something external "Lit the Fire".
Some considerations;
1> A wire strand out of place and bridging the terminals. (Do you use extra flexible wire?)
2> With the high humidity, you may have had some drops of water from condensation fall on the terminals. (Look for a low point in the cabinet construction above the breaker from which condensation could gather and then drip onto the terminals).
3> Workmanship. It's possible that a wire strand or something else conductive was left in the cabinet. The equipment passed the shop tests but somewhere in transit, something moved and ended up on the terminals.
4> Sabotage. Be careful with this one. I have seen penetrox used as "Job Security". If it was sabotage, it may not be wise to show any suspician whatsoever. One "Accident" may lead to another. When I was young, an old timer told me, "I never wanted to be the smartest, I always wanted to be the oldest!"

If you have breakers on everything in the panel you may be able to megger your connections from the disconnect to the small breakers to locate any further problems before you energise again.
yours

 

[jraef]

All good answers, but I'll add another issue to consider.

Mini Circuit Bbreakers (MCBs), ABB or otherwise, are not the same as what you might consider to be "regular" circuit breakers. They are technically "supplemental circuit protectors" by UL classification, and must have upstream current limiting fuses that keep the available fault current at the MCB line terminals lower than what you may be used to. In the case of the Pro-M Series from ABB, that may be as low as 5kA depending on size. So if you have a fault downstream and your upstream fuses don't clear before it reached 5kA, the breakers would be subjected to electro-mechanical stresses they were not designed to withstand.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[Barrie66]

To Waross/Jraef,
First of all, the wiring connections were contained within pin connections and wire strands could not be loose to cause a short circuit. Also the wiring terminal entries are about 1/2" below the terminal screws where the flash over occurred. The flash over/short was between the terminal screws. The control panel had been livened maybe 7 or 8 times before the failure. There definitely was not any moisture present in the panel. Also not mentioned in my post is that the mini breaker is rated for 10kA....
As mentioned also in my post, the upstream current limiting 150A fuses interrupted the circuit to the live side of the 2 pole breaker which is where the flash over occurred.
With regards to "sabotage" I can rule this out as the unit had been livened several times immediately before the failure.
All your points are well taken, however my question really was whether anyone had experienced similar problems with these breakers. The breaker is marked for 480/277V and has been approved by most of the worlds testing authorities, however as the spacing between the phases at the terminals is just 3/16". (5mm) it seems that given the right circumstances flash overs could occur.

 

[davidbeach]

What was the power system you were connecting to? Any chance that it wasn't solidly grounded? Any chance there were any overvoltages?

 

[jraef]

The centerline distance between terminals isn't as important as the total contiguous linear surface distance between conductive parts, known as the creepage distance. Under UL rules (which is what I am familiar with), on 600V class devices that creepage distance must be at least 1 inch. IEC most likely has similar rules, but they tend to classify devices at 415V and then again at 690V. It doesn't appear that those devices are 690V rated, so I'd say they probably just barely passed UL at 600V under the 1 inch rule.

I have had those type of breakers fail, although not ABB, but to be honest after the failures of other brands I refuse to allow their use so I've never used ABB. I don't like the design in general. Although they passed UL-1077 as a "suplemental circuit protector", that UL standard was created from whole cloth specifically for these type of devices because they would NOT pass the UL-489 test proceedure used for circuit breakers. That alone worries me.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[Barrie66]

To davidbeach
I'm not sure whether the 480V system is solidly grounded. But will find out later this week when I return to Mexico.
I wouldn't believe there is over voltages as the substation from where it is fed is within 200'. I did check voltages and found them to be 474/474/474 at the equipment.

To Jraef
Thanks for your comments. As mentioned earlier, the breaker ABB S262 C3 is marked to IEC947-2 Icu 10kA and has approval stamps for most countries and shows 480/277V as well.
Thanks to you both.