STRENGTH OF PANEL COVER IN RELATION TO ARC BLAST

bobby ocampo

Senior Member
What is the strength of Panel board cover, switchboard cover in accordance with Arc Blast? Do you have a table of the Cover Strenght in relation with the thickness of the metal?
 

Jraef

Moderator
Staff member
If the gear in question is not listed as Arc Resistant, it's irrelevant in that the cover is not actually required to remain intact in an arc blast event. There are no standards other than those for Arc Resistant Equipment that address this one way or the other. From an electrical and arc flash safe work practices standpoint in NFPA 70E, you are not actually required to use PPE or other protective measures if the enclosure is closed, even though there is no guarantee that it will not come apart in an arc blast event because the risk of that is considered low.

If the gear is listed as Arc Resistant, the thickness of the metal is whatever it takes to withstand the forces of the available incident energy it is rated for. Manufacturers attain that with a number of strategies involving forming and bracing, not just metal thickness alone. Certification is attained only by destructive witnessed testing at qualified facilities.
 

Coppersmith

Senior Member
I'm sure how strong they are, but I will usually shield myself with the panel door when I flip on a breaker.
 

bobby ocampo

Senior Member
If Arch Flash Suit has a rating why will a cover or the thickness of the panel metal sheet have no rating? :weeping::weeping::weeping::blink::blink:
 

bobby ocampo

Senior Member
If the gear in question is not listed as Arc Resistant, it's irrelevant in that the cover is not actually required to remain intact in an arc blast event. There are no standards other than those for Arc Resistant Equipment that address this one way or the other. From an electrical and arc flash safe work practices standpoint in NFPA 70E, you are not actually required to use PPE or other protective measures if the enclosure is closed, even though there is no guarantee that it will not come apart in an arc blast event because the risk of that is considered low.
How come that some metal covers are thick and others like panel board are thin? How will a panel builder decide what thickness to use in the cover? How do they decide to determine the strenght of the cover?

If the gear is listed as Arc Resistant, the thickness of the metal is whatever it takes to withstand the forces of the available incident energy it is rated for. Manufacturers attain that with a number of strategies involving forming and bracing, not just metal thickness alone. Certification is attained only by destructive witnessed testing at qualified facilities.
What specific UL test standard do they use in the test for panelboards and switchboards?
 

Jraef

Moderator
Staff member
If Arch Flash Suit has a rating why will a cover or the thickness of the panel metal sheet have no rating? :weeping::weeping::weeping::blink::blink:
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
 

Jraef

Moderator
Staff member
How come that some metal covers are thick and others like panel board are thin? How will a panel builder decide what thickness to use in the cover? How do they decide to determine the strenght of the cover?



What specific UL test standard do they use in the test for panelboards and switchboards?
There are no UL standards for Arc Resistance. It is covered by ANSI
ANSI/IEEE C37.20.7 defines switchgear arc resistance in two basic categories:

ANSI type 1
Arc resistance from the front of gear only
ANSI type 2
Arc resistance provided from the front, sides and rear

A suffix may be added to either of these two types to further define the type of protection provided:

A: Basic design
B: Arc resistance is maintained even while opening designated low voltage compartments
C: Arc resistance is maintained even when opening designated adjacent compartments
D: Special designation that supplements the Type 1 designation, but identifies additional arc resistance in certain structures

This standard is actually for MV equipment, but because it is the only one so far, most people making Arc Resistance LV gear are using this as the test standard.
 

bobby ocampo

Senior Member
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
If there is an ARC blast when cover is closed, the cover should be the first line of defense. Panelbuilders should know the arc flash/blast rating of the cover. Cover should be properly bolted to make sure that it will not be blown away.
 

jim dungar

Moderator
Staff member
Panelbuilders should know the arc flash/blast rating of the cover.
There is no industry standard methodology for calculating arc blast. Arc blast and arc flash incident energy are not directly correlated. High arc flash incident energy is often associated with arcs lasting for several seconds, while arc blast occurs in just several milliseconds.

I have heard of and seen panel cover/plates flung open, usually due to the fasteners failing, and have seen ones with holes burned through them, but I have never seen one that was actually turned into shrapnel.
 

bobby ocampo

Senior Member
There are no UL standards for Arc Resistance. It is covered by ANSI
ANSI/IEEE C37.20.7 defines switchgear arc resistance in two basic categories:

ANSI type 1
Arc resistance from the front of gear only
ANSI type 2
Arc resistance provided from the front, sides and rear

A suffix may be added to either of these two types to further define the type of protection provided:

A: Basic design
B: Arc resistance is maintained even while opening designated low voltage compartments
C: Arc resistance is maintained even when opening designated adjacent compartments
D: Special designation that supplements the Type 1 designation, but identifies additional arc resistance in certain structures

This standard is actually for MV equipment, but because it is the only one so far, most people making Arc Resistance LV gear are using this as the test standard.
Any table on Cal/cm2 of metal sheet?
 

bobby ocampo

Senior Member
There is no industry standard methodology for calculating arc blast. Arc blast and arc flash incident energy are not directly correlated. High arc flash incident energy is often associated with arcs lasting for several seconds, while arc blast occurs in just several milliseconds.

I have heard of and seen panel cover/plates flung open, usually due to the fasteners failing, and have seen ones with holes burned through them, but I have never seen one that was actually turned into shrapnel.
If they can test arc suite and have a rating of cal/cm2, then why can't they have a rating for metal sheet based on its alloy or thickness? Arc flash and blast are being calculated to detemine the rating of Arc flash. Impossible that they can't calculate arc blast/flash rating of the metal sheet and the strenght of how the cover should be bolted.
 

jim dungar

Moderator
Staff member
Any table on Cal/cm2 of metal sheet?
Arc flash PPE is rated in Arc Thermal Performance Value (ATPV) which is in the units of cal/cm[SUP]2. [/SUP]Effectively, this is the amount of heat that can be absorbed by the PPE while allowing about 1.2 cal/cm[SUP]2[/SUP] to be transferred to the wearer.

An ATPV rating is not applicable to a heat radiator like a steel panel.
 

Jraef

Moderator
Staff member
I have a GIF movie of an MCC feeder bucket blowing open and the door coming off, but apparently this site won't accept GIF movies.
 
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