ECN Forum Forums Code Related Discussion NEC & other Code issues 300amp main blew apart?????

Hello all, Wanted some education from the guro`s We had a 300a main just blow apart internally it appears yesterday.No one was injured thanks to the right hand turn on and turn away method.We meged all the lines and couldn`t find a problem anywhere. This circuit had been off for approx. 30-40 days.The area is not moist or damp, humidity maybe. It was a square D big frame I don`t have all info in front of me.If you guys could help shed some light on this it would be much appreciated.PS one of the crew already figured it out he says sh** Happens.Maybe he`s right but I figure we can do better.

Anything man made is subject to failure unfortunately. Maybe since the breaker is not swiped that often the tripping mechanism was stiff or ceassed and a load elsewhere in the building called for the main to trip and since it could not it blew apart from the force (high ampacity) of the short circuit. It could be anything. Maybe your man is right it just simply failed.

Since it had been off for 30 or 40 days,I assume you must have been doing work downstream of the main.Were the lines you mentioned megged prior to turning on the switch? It could be possible that you had a fault that cleared itself once you energized it.

Reel-Break...with the eguipment off for 30-40 days is there anyway a rat or modent could have gotting in there.we had a 13.2 outside switchgear.and the rats would trip out the gear 2 or 3 times a year.no more rat.

glad to hear no one got hurt.

Were you closing on a load or just an open circuit say to a DP with all breakers off?

Please explain the "right hand turn on and turn away method" as it sounds to have done its job in this case.

ThinkGood,

The method for closing breakers is to reach for the handle, then turn away from the panel with the breaker behind you. Don't look at it. Throw the handle.

This way, any arc-flash is likely to not injure your face, and one tends to run when things are exploding around them, so having your feet facing away from the panel will keep one from running into the arc-flash.

Make sense?

Being left handed, I'm not sure of the significance of using the right hand, unless it is to place less risk on my dominant hand, but that only works for lefties!

Left handed people are in their right mind!



-Virgil

I am more familiar with the "left hand rule". As most disconnect operating handles are on the right hand side, the practice is to stand to the right of the enclosure, turn your face away, and operate the device with your left hand. Either way, the fundamentals of staying to the side of harms way, and turning your face (eyes) and feet away from a possible explosion and/or flash are good practice.

Interesting I`ve always been told the hinges are on the left facing a discon.And thats it`s stronger side. The latches to hold the door closed are on the right. the door if blown open it`s weaker at the left towards the handle so turn on with right hand face away and if blown open the door will hit your forearm aide in head start for the truck.All the breakers or doors I`ve seen have blown open at the door from the handle side where the latches are.All the down stream loads were off when the main was energized thats what puzzled everyone.We had installed a 37.5 kva buck boost to supply an rf dryer but all the disconnects were off and were doulble checked to make sure they were actually off.