Arc Flash/Resistant

[tulum]

Hello all,

For some reason the search function is not working right now...so before I forget I will post my question anyways.

What is the difference between Arc Resistant, and Arc Flash?

It was my understanding that Arc resistant was a type of switchgear that under a faulted condition the gas pressure would be routed away from any personnel through the roof etc. It was also my understanding that Arc flash was a study that determined how far (or what type of protective clothing) a person had to be from an enclosure to be safe.

I was recently told by a manufacturer rep that eventhough you buy arc resistant gear, you still have to wear the arc flash protective gear? That the two have nothing to do with each other?

Can someone please explain?

Best Regards,

TULUM

 

[davidbeach]

Arc Resistatnt gear meets certain performance specificatons with all of the doors closed. Once you open a door of the gear to do anything there become an arc flash risk.

 

[tulum]

Sorry I should re-word the above.

The manufacturer rep said that even with the doors closed the protective gear would need to be worn when within a certain area due to current standards?

I know it sounds strange, but anyways just want to clarify.

regards,
TULUM

 

[MakeItSpin]

70E says at certain energy levels operating a metal clad switch over 1kV with the enclosure doors closed requires Category 2 PPE.

I don't believe that 70E addresses "arc resistant" gear, any 70E experts care to comment?

 

[dpc]

I think it is true that NFPA-70E does not specifically address arc-resistant switchgear. This seems understandable considering the small amount of arc-resistant switchgear in existence.

However, I think it would be reasonable for a company to develop safety rules related to work around arc-resistant gear that took its protective function into account.

Also, there are different levels of arc-resistant gear - some is designed such that only the front of the gear is rated to withstand arcing faults. I think the Canadian spec has three different categories. I'm not sure about the new ANSI spec for arc-resistant switchgear.

 

[acwalsh]

The last post was a long time ago but I'll offer this for what it is worth. I have just returned from a seminar on electrical safety where much of the focus was on arc flash hazard, NFPA-70E and PPE. One of the speakers, a consultant who ran a test lab for the former Ontario Hydro stressed that the hazard is reduced to Category 0 when the doors of switchgear or motor control centres are closed. Put simply, opening a disconnect or circuit breaker using a door mounted handle, requires no additional PPE; inserting a bucket into a live MCC requires an arc flash analysis to determine the appropriate PPE.

 

[dpc]

acwalsh -

The notion that having a closed door on an MCC bucket reduces arc-flash risk automatically to Hazard/Risk Category 0 is controversial at best. (Category 0 does NOT mean zero risk by the way).

NFPA-70E does not say this. There is a table in NFPA-70E that may be used "in lieu of" an arc-flash hazard evaluation that does give a Category 0 to certain tasks on MCCs when the bucket doors are closed - but within certain short circuit and clearing time restrictions.

Except for arc-resistant switchgear, no electrical equipment is tested for its ability to withstand arcing faults. It's easy to conduct arcing tests in MCCs that will blow the bucket doors completely off.

Closed doors are a good thing, but do not guarantee protection.

 

[Dumbo2929]

Category 0 is simply below the level of 2nd degree burns, 1.2 cal/cm2 for 1 second at 24". I have witnessed factory tests of arc-resistant switchgear, in which the blast is funneled up and out, away from the front of the gear. Early arc resistance gear tried to contain the blast; now the second generator creates a path away from where personnel will be standing to channel the energy. A qualified person would be foolish to rely on the equipment manufacturer to protect them completely. Also the speed of upstream protective devices varies, and the exposure could be for longer duration, increasing the danger.

 

[dpc]

The Category 0 defintion can be confusing, but basically, Category 0 applies up to 2 cal/cm2 of incident energy. See NFPA-70E 130.7(C)(5).

Category 0 requires non-melting clothing (generally cotton), but the clothing is not required to carry a specific arc energy rating.

 

[mykh]

Would be interesting to know what transmission utilities are doing about legacy arc flash issues relating to old switchboards that have long fault clearance times due to grading with downstream protection and simple protection schemes such as no bus zone or differential protection.