Bus bar problem.

[Tiny Spark]

Hi Everyone!
I am new here as you will have noticed, Ive never really bothered signing up to any electrical forums as I am usually a browser but something happened to me the other day which has prompted me to do so!

So here it is and I am hoping someone may be able to enlighten me as to what possibly went wrong as I dont mind making mistakes etc as long as I can learn from them!

So I was working on a 200v 3 phase bus bar system after we had just installed a new machine into a existing tap off box, As the tap off box had been unused for a while I wanted to check that the supply to the box was ok before carrying on.
So using a Megger all in one I proceeded to take a voltage measurement between 2 of the phases of the incoming side to the tap off box isolator (cant remember which).
At this point there was a almighty flash and a bang and sure enough one charred box and a dead bus bar system!

I am happy to report that I am totally fine and suffered no injuries, however the same can not be said for my test leads which are somewhat shorter than when they started!

Now sadly (or gladly not sure which) I remember little of the incident other than me swearing lots and the flash bang, I thought I may possibly of somehow caused a short between the phases and the enclosure of the tap off box but I think the gap between the shielding and the connections would of been to large for this.
Or possibly I had some kind or arking between my probes and the connections.

Obviously its pretty much impossible to tell what actually happened but I am hoping someone may have a theory or even had some horrible experience of this themselves?

I Feel a little traumatized by the whole thing but more so because I just dont know what happened!

Anyways any help appreciated, Thanks.

 

[Engineer54]

As sure as eggs are eggs, you somehow managed to short the two phases out or shorted a phase to earth. Check your probes(or what's left of them) and the location where you conducted the test. You should be able to see exactly where the short or shorts occurred.

 

[shagbite]

a photo of the crime scene would be nice - if the forum will allow it.

 

[ian.settle1]

a photo of the crime scene would be nice - if the forum will allow it.

He might blow that up as well

 

[ruston]

He might blow that up as well

It's called enlarging , same as his posterior when it went bang.

 

[Engineer54]

As an update to my original post above, check that the Bus Bar insulator/supports are still in place and fixed to the metal housing. You could have inadvertantly pushed a little too hard on the probes moving the unsupported bar into another or onto the earthed casing?? But please, turn the Bus Bar system OFF first!!! lol!!

 

[ruston]

Yup because the problem is unlikely to be through the megger , unless you are just setting us on lol. Pics would be nice lol , as has been said.

 

[Tiny Spark]

As an update to my original post above, check that the Bus Bar insulator/supports are still in place and fixed to the metal housing. You could have inadvertantly pushed a little too hard on the probes moving the unsupported bar into another or onto the earthed casing?? But please, turn the Bus Bar system OFF first!!! lol!!

Thanks for that,
I will get the box off the bar next week and have a good looksy.
Ime just really stumped as to how I managed it to be honest, I test 3 phase systems on a regular basis but usually hard wired rather than tapped off bus bars so I was wondering if I had missed something stupid.

And yes my backside did enlarge somewhat but had to get it quickly back into position so I could get the power back on to rectify my cock up!

Needless to say though I had a case of the shakies afterwards and had to chill most of the day afterwards!

 

[Darkwood]

As you are unaware of the cause you should not re-energise until you can ensure the busbar and assembly are sound and hopefully you did an insulation test before if you have already energised it .... a common cause is adding to E54 post is heat damaged cables for what ever reason that may be laying against another conductor and the insulation has broken down but still in tact and as you may have disturbed it the cables could have shorted....

I doubt its your leads to cause the issue as the crock clips or probes shouldn't be physically possible to bridge the gap between phases or down to N/E.