Flash Over Due to Short Circuit in Busbar Connection Side of MCCB

The cause was not having a safe method of work in place before the work started.

• The bars should have been locked off, tested, and a Permit To Work document raised before the panel was opened. Instead, a metal object came into contact with at least one of the bars and earth, or at least two bars while the panel was being opened and at least one of the bars was still live.

Further comments may prejudice any future prosecution case and are to be vigorously discouraged.

You'll probably never know the answer.

It could have something to do with the external fire maybe melting some insulation from wiring, and movement occuring when he opened the door, all the way to having an insect happily nesting in there, that got startled when he opened the door and shorting things out.

I hope the guy is okay...it sounds like a dangerous place to work.

Contact the MCCB manufacturer, find out if there's a known problem. They should have been your first phone call. They may do an investigation for you.

I had a MV OCB fail, the manufacturers were there in a couple of hours.

Your "electrician" is very lucky. I hope that your company and this worker use this incident to change your methods.

The Bakelite cover is now plated with the remains of the metallic material that vaporized in this arc flash. If you can do a chemical analysis of this coating to identify if this is copper, aluminum, steel or some other metal then you will have a good start on the process of finding out what happened. This material could be wire remnants from an earlier poor insulation stripping, hardware left by sloppy work (nobody is perfect) or almost anything else left in the chassis. The added heat from the fire could have distorted sheet metal so that just opening the door now caused a short circuit.

Getting back to your methods. This fire happened three days before this incident. Power to all devices in the fire zone should have been turned OFF from a location not affected by the fire for inspection prior to any attempt at operation or servicing. This simple step takes far less time than any aftermath accident like the one you have now.

As said, you may never know the exact cause, but here is a likely candidate:

In the previous fire, you indicated that the insulation of the motor feeder cable burned. If the circuit was energized at the time, the burning insulation could have allowed a high resistance arcing fault, too high of resistance to cause the MCCB to trip on instantaneous, but the incoming power was likely killed in the firefighting attempt before the MCCB had a chance to trip on thermal over current. So when the fire damage was repaired and you saw that this breaker had not yet tripped, it gave you a false sense of security. But nonetheless, the cables FEEDING the MCCB were compromised by the heat of that over current and the insulation was damaged, possibly even carbonized, and/or the dust that had settled on it carbonized. When your electrician went to remove it, the failed insulation could not prevent a flashover between phases or ground, because it had lost its dielectric properties.

This is why, as the others have mentioned, you need carefully considered and executed restart procedures that include re-testing of all insulation values prior to energization. The pressure from management to get back into production is ALWAYS there, but prudent safety procedures must be in place ahead of time to forestall such a tragic consequence. I hope your electrician's injuries are recoverable, but I fear the are likely severe.

Given what we've been told, this is a strange one. Before we start awering questions, it is important to note that this a prime example of why despite what we think we know, it is imperative to wear PPE (Personal Protective Equipment) whenever working around anything that we have not personally made dead...

So now you have a flashover that just happened to occur when someone opened the front cover of a MCCB, and you can't even tell us from the evidence that only you can see, what the flash-path was. I will not repeat all the operational warnings that others have rightfully mentioned, so let's dwell on what you didn't tell us.

1. Why was the electrician opening the door?

2. What is the product in the plant?

3. Is it conductive?

4. What is this breaker's relationship to the motor feeder that was on fire?

5. How are the feeder cables brought into the MCC?

6. Are there any seals or glands between the motor and the MCC?

7. Is this MCC in a conditioned space?

8. Is it under positive or negative static pressure?

9. When was the last time the entire MCC cleaned/vacuumed?

10. Are there any Classified Areas nearby?

11. What finally cleared the initial fault/flashover at the motor?

12. What protective device(s) cleared the fault at the MCCB?

13. What exactly was going on in the rest of the plant under both of the above scenarios?

14. Why can't you determine the exact nature of the flashover by examining the track of the flash residue?

15. What are your ambient conditions such as high heat, high humidity, near bodies of water, salt water, coal dust, wood dust, metallic dust, explosive/corrosive fluids, steam/fluid leak?

16. Your pictures show a relatively clean device, was it removed that way or was it vacuumed off or in any way cleaned up?

17. When was the last time the MCCB was operated, tested, repaired, rebuilt, etc.?

18. Aside from the megger were any other tests performed after the incident?

19. What were the results of testing the motor, its controls, feeder cable, terminations, etc.

20. Has the motor and its associated equipment been returned to service?

There you are, twenty questions to save us the usual back and forth. You might as well answer them in advance because your management, insurance carrier, and your lawyers are going to ask those and more soon enough.

Way back in my Navy days, we had this simple system called "tagged out".

Physical, (signed), red tags were placed on electrical components, all the way back to the source. No doors were opened, nor work done, until everything was signed off as dead.

It worked pretty well.

I had the similar experience it was failure of bake light insulation the expert consultant briefed me Bake light insulation fails under certain conditions

Isolating a panel is not always possible, cubical isolation is.

We don't know enough about the design to really make any real suggestions.

I'll quite happily change a 800A FSU on to live 3200A bus-bars. I know the system and the equipment.

Re: Flash Over Due to Short Circuit in Busbar Connection Side of MCCB

I have to agree with what has been said previously in some replies. The busbar should have been isolated before opening the panel door, especially when you know there was fire damage.

Beside the 'what he should have done" is now irrelevant, it has happened. however the cause could possibly have been due to carbonising from the fire damaged cable not having been properly cleaned away from ALL surfaces of the cubicle, breaker components or from the cable gland plate. An inrush of air when opening the panel door could have dislodged a piece of carbonised material, which may have seemed fine, solid, connected and safe, and this falling between the busbar, caused a flash over, resulting in the force (flash), taking the least path of resisatnce, i.e. via the now open panel door.

This type of flash will never be discovered as the flash will have created further damage, and materials destroyed or blown away in the flash, that may have caused the flash over when the door was opened. If the flash occurred as soon as the door was opened, it could possibly have been further oxygen being added to an existing arc occurrence.

Unfortunately you now only have speculation and possible causes and theories, none which will help you now, as there may be many possibles, but no actual causes, as the factor of the cable fire, would point towards the final result. Without knowing how clean the cubicle was made and if all traces of carbonising were removed, after the cable fire, you have only a 'possibles' and no further trail to follow as it has been blown away and further damage made.

The breaker should have been totally removed from the cubicle, fully cleaned and refurbished, tested, the cubicle cleaned and production could wait a few days. An ounce of prevention is better than a pound of cure in this case.

I hope the lad who opened the door is not badly burned and injured.

TIP 1: egg whites are fantastic for burns.

TIP 2: Now have a shutdown and clean all the affected panels surrounding where the cable was on fire, before this happens again.

Tip 1 is an internet gem that is false, eggs may contain salmonella, placing egg whites on an open wound provides a really easy path for bacteria entering the body. Read this entire article for more info:

http://www.snopes.com/medical/homecure/eggwhite.asp

Very interesting RAM Consult. Read the article and it states, 'may contain salmonella" However, it worked form myself after taking 33kV on my left arm and I do swear by it. But as is inevitable. one mans meat is another mans poison. But, duely noted. Thanks for the article lead.

Having personaly experienced contact and extensive burns from 13,800VAC in my past and suffering through a long intensive, painful recovery I feel it appropriate to share a little information here. (Still have issues.)

Pasturized Aloe Vera gel is without a doubt the best alternative to the "mainstream medical" treatments for treating burns.

I was scheduled for multiple skin grafts and was going through multiple tissue debriment treatments with salt water baths when a friend shared this jewel with me.

Within three days from starting the use of the Aloe gel my replenishing growth rate for new tissue doubled and within 9 days all of my skin grafts were cancelled.

My assigned plastic surgeon at the burn center was amazed and has since gotten very involved in promoting research and the use of Aloe for burn treatment as he had never witnessed anything akin to my progress in his career.

The outside of the body is but a mere portion of what goes on inside and there is only one facility in the USA that successfully treats MV and HV contact victims.

It is located at the University of Chicago and is a life saving miracle.

My guess on the cause of this incident was that the cable insulation integrity was violated by the high temperature of the fire and the fault closest to the MCC occurred at or near the same time as the door opening due to movement of the conductors.

Sorry your person was hurt, but it appears you have no flash protection requirements in place. Also appears that the unit you have in the picture has no business being in a MCC unit. But at any rate, If your in the US you need to get a copy of the Arc Flash safety requirements and get the proper materials to work on these units safely. If your in another country that has no requirements then get a copy of the OSHA Arc Flash requirements off the internet.

I routinely work with 4160 and 13.8 K voltages. Rule number 1. follow safety requirements for Arc Flash. Rule 2. make sure the loads are off everything being disconnected. Rule 3. Only experienced skilled trades allowed near units being de-energized. Rule 4. Follow all above and go home safe.

The most likely cause of the flash over is a short between 2 phases on the breaker input side, caused by a metallic object falling on that area or from inadvertant action by the electrician, using a metallic tool to investigate the connections, ignoring the fact that the supply was still on.

Look for a missing bolt, nut or any part from the busbars or any place above the breaker, in such a position that it will fall to that place (input side). Also, check the tools that the electrician uses normally in his tool box or in the area, for any damage due to such shorting (Melted part...).

Since you asked for the possible cause, there you are: look for any missing metallic object or part of a metallic object or tool. That is, if the electrician did not started to remove the breaker already, while the power input was still on. This is as blunt as I can go.

All that is due to the negligence in not having a strict code for doing such activities. these procedures are necessary to protect operatives from their possible mistakes (Which we are all prone to have from time to time). Safety first always, then repairs.

This kind of flash over happened once when an electrician decided to work on a live Busbar and dropped a nut by mistake, big enough to short 2 bars. It blew out spraying metal all over his cloth. he escaped with damages to his clothing only. He will never attempt this stunt again!

in addition to the comments and suggestions of the members here i would advice have a weekly inspection of your electrical pannels trgting of all busbar&Busbar Link bolts, inspection of contactors clean with 100% sprit,using a vaccum cleaner remove as much dust as possible from all your electrical panels,.check tightness of control circute screws of lugs,i assure you that you could achive flash over free operation of your electrical panels.i ahived zero down time on my electrical panels for months to gether only issue is you need to work on weekly holydays of your establishment good luck

I've seen several breakers in motor control panels blow because work was being performed on a panel above that had been locked out and a screw dropped down through the raceway. One actually was in contact with a single phase and when the disconnect was turnedoff it dislodged the screw to cntact the other phase. Had the employee been aware it was present, he would have turned off the feeder lines to the set of panels. That's why EWP protective measures are in place. All our personnel are trained to category 4. Arc flash is not user friendly.