Attached are pictures of a fused disconnect switch which arced when the handle was being operated from closed to open position. The door blew open but person was standing to the side to operate. The cause appears to be the operate mechanism was rubbing a wire which was run past the mechanism and eventually wore the insulation off.

There was a study done at this facility in 2010 and they are now going to update the study. The 2010 study had the bolted fault current at 7.388kA and arcing current at 4.894kA with 0.3 cal/cm2 incident energy at this disconnect switch.

The facility is also inspecting all other similar disconnect switches.

Hi Barry

Greetings from North of the border. Yes it is plenty warm up here I was wondering if I could please have your clearance permission to reproduce your post with the photos? They will be strictly used for training purposes up here and I would like to insert into my next monthly newsletter

Thanks Barry

Best regards
Len Cicero
Burlington, Ontario

This accident is a perfect example of what I talk about in our Electrical Safety Seminars. I always ask the electricians if they or one of their co-workers have ever experienced electrical equipment having a short circuit or arc flash event. Almost all say "yes". Luckily, electrical equipment is very reliable but even brand new equipment can fail.

Always be prepared for that "Electrical Bomb" to go off.

I was glad to hear that the operator of the switch was standing off to the side. We stress this as well in our classes. Doors rarely contain a large arc flash event unless the equipment is arc flash resistant MCCs or Switchgear.

The root cause of this electrical explosion was a result of the switch being installed incorrectly a violation of the national electric code. An inspection of the original installation would have revealed incorrect bending radius and routing of wiring internal to the switch enclosure. Applicable electrical standards require equipment maintenance, maintenance allows for visual inspection of conditions likely to lead to failure. Just as switches have been damaged by installation at locations outside of their UL listings and failed, The switch mechanism itself and the enclosure appear to have functioned as designed and listed.

This incorrect installation is why the electrical safet standards requires work involving operation of energized electrical equipment be evaluated and assessed for potential dangers before the work takes place.

Shame on the original installer and a caution to users of electrical equipment that they must remain aware of the condition of their installed electrical equipment, after the contractor has left.
Was this installation inspected , not very well.

Is that a factory knockout? There are others that appear to be in more appropriate locations.