1. Junior Member
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## PPE

We have arc flash ratings labeled on our switch gears and one of them say 40.38 cal. Should we buy a 50 cal? And anything pass 40 cal ( even if it's that .38 ) is that pretty much a major kaboom ?

2. Originally Posted by Ray83
We have arc flash ratings labeled on our switch gears and one of them say 40.38 cal. Should we buy a 50 cal? And anything pass 40 cal ( even if it's that .38 ) is that pretty much a major kaboom ?
40 cal. is the peak level breakpoint.

what i was told by the fellow who gave me my arc flash training
is that ppe levels above 40 calorie didn't accomplish much, as a
level much above 40 calorie will result in an explosion that will
kill you from the concussion.

if you are, for whatever reason, in a hot work situation with an
arc flash rating above 40, you really need to pause and rethink this.

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Originally Posted by Fulthrotl
what i was told by the fellow who gave me my arc flash training
is that ppe levels above 40 calorie didn't accomplish much, as a
level much above 40 calorie will result in an explosion that will
kill you from the concussion.

This type of 'fear statement' was commonly taught more than 10 years ago. However, the concussion force, arc blast, and the incident energy, arc flash, are not directly related.
It is very easy to have incident energy levels >40cal/cm^2 when the protective device does not clear due to relatively low arcing fault currents. This is why many people use a 2 sec cut off for their calculations.
Even levels <40cal/cm^2 can have an 'explosive force' which can produce shrapnel and concussions.

I believe the 40cal/cm^2 clothing 'limit' is likely to be removed in the 2018 edition of NFPA70E.

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A calorie is a measure of heat energy--in this case, heat energy at the arc. Energy of an arc in open air will be released omnidirectionally. An arc in a box will be contained until the box ruptures, producing a greater concussive wave, particularly when copper inside the box expands when it melts, possibly moving to its plasma phase.

5. Originally Posted by jim dungar
I believe the 40cal/cm^2 clothing 'limit' is likely to be removed in the 2018 edition of NFPA70E.
granted that there was an applied fear factor in the training i was given,
and it was 10 years ago.

so then levels of protection may be calculated above 40 cal, and required?

note to self: if a level of protecting above 40 cal. is required, i don't need
a thicker suit. someone else needs a thicker suit.

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As noted by others, 70E pretty much tells you to de-energize above 40. Have you filled out an energized work permit for this to validate the need?

Is there a maintenance mode for arc energy reduction? Or access to the study software files to understand levels when the instantaneous is dialed all the way down?

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If you stood an extra inch farther away you'd probably be under 40 calories but I don't think you're allowed to take credit for that extra inch. I think at some point NFPA 70E is going to have to take practicality into account. I think NFPA is afraid of being sued so they are making it almost impossible to do anything.

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Originally Posted by petersonra
I think at some point NFPA 70E is going to have to take practicality into account. I think NFPA is afraid of being sued so they are making it almost impossible to do anything.
NFPA70E-2015 says that a risk analysis (e.g. sanity check) must be performed to determine if the hazard will occur. After the risk analysis is done, steps be taken in order to mitigate the hazard. The very last thing to do is select appropriate PPE, partly because of limitations on it effectiveness.

An argument can likely be made that NFPA-70E wants to reduce, if not out right ban, energized work.

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Originally Posted by jim dungar
An argument can likely be made that NFPA-70E wants to reduce, if not out right ban, energized work.
Agree. Really, the only live work that should be justifiable is IR scanning.

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Originally Posted by publicgood
Agree. Really, the only live work that should be justifiable is IR scanning.
There is also some troubleshooting that requires energized equipment.

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