STRENGTH OF PANEL COVER IN RELATION TO ARC BLAST

[Jraef]

It sounds like the fasteners failed. Did the door turn into shrapnel?

Door became a projectile, yes. The definition of shrapnel includes “... or other object thrown out by an explosion.”

I was at work when I was trying to post that image, but we are restricted from accessing any image hosting sites. I’ll have to bring my PC home to try to post it or email it to myself first (I use my iPad at home but that image is not on my iPad).

I got that image when I worked for Siemens during a training class on retrofitting new breakers into old switchgear and MCCs. It was used as a warning to us on the dangers of not paying attention to the available fault current. The image is a brand new Siemens breaker with too low of a fault rating put into an old MCC bucket and blowing apart under fault current stress, taking the door with it.

 

[jim dungar]

So it was an improperly applied (under rated) breaker that exploded, not simply a door failing during an arcing fault event.

 

[bobby ocampo]

Different issues. An Arc Flash Suit protects you from being burned. What I mean by "no rating" is that if there is an arc BLAST inside of the equipment, a cover blowing open can become shrapnel and kill you, suit or no suit.

https://www.youtube.com/watch?time_continue=132&v=9lbiYAMsOEY
Action happens at around 1:50

These means that the equipment should have a rating. One is the strenght of the cover and another is the strength of the bolt of the cover. If there is an arc blast inside the enclosure, common sense will dictate that the cover strength should be sufficient to protect the person in front of the switchgear or motor control.

 

[Jraef]

These means that the equipment should have a rating. One is the strenght of the cover and another is the strength of the bolt of the cover. If there is an arc blast inside the enclosure, common sense will dictate that the cover strength should be sufficient to protect the person in front of the switchgear or motor control.

You would think so, but doors staying closed during an arc flash / blast event is actually NOT a requirement of the equipment design under UL, NEMA etc. The only place it becomes addressed is in the requirements for equipment that is specifically labeled as "Arc Resistant" and tested under ANSI C37.20 or the equivalent IEEE spec.

 

[bobby ocampo]

You would think so, but doors staying closed during an arc flash / blast event is actually NOT a requirement of the equipment design under UL, NEMA etc. The only place it becomes addressed is in the requirements for equipment that is specifically labeled as "Arc Resistant" and tested under ANSI C37.20 or the equivalent IEEE spec.

If it not a requirement then what is the use of having a cover or to have a thick cover in switchgears and motor controls?

If ANSI Requires it then there should be a rating for the thickness of the sheet. Otherwise how will they calculate the thickness that will pass the test as Arc Resistant?

 

[mbrooke]

Different issues. An Arc Flash Suit protects you from being burned. What I mean by "no rating" is that if there is an arc BLAST inside of the equipment, a cover blowing open can become shrapnel and kill you, suit or no suit.

https://www.youtube.com/watch?time_continue=132&v=9lbiYAMsOEY
Action happens at around 1:50

Whoa!

Wonder what went wrong.

 

[zog]

If it not a requirement then what is the use of having a cover or to have a thick cover in switchgears and motor controls?

If ANSI Requires it then there should be a rating for the thickness of the sheet. Otherwise how will they calculate the thickness that will pass the test as Arc Resistant?

You seem to only be reading half of Jraefs posts. There is an ANSI standard for arc rated switchgear, which requires special design elements to be able to re-direct the arc blast. If your gear is not specially designed to be arc resistant then it was not designed or tested to be able to contain an arc blast so you cannot assume the covers will contain the blast.

Here is an example on a job I was on a few years ago

 

[zog]

And here is a good presentation on the subject

http://www.wmea.net/Technical Papers/0516_Arc_Resistant_Switchgear_Eaton_May_2016.pdf

 

[jim dungar]

If it not a requirement then what is the use of having a cover or to have a thick cover in switchgears and motor controls?

The cover is there to prevent access to internal components such as energized parts. The thickness of the cover has to door with its structural integrity. a 12"h x 15"w MCC bucket door does not need to be as thick as a 72"h x 36" wide switchgear door that will have components mounted on it.