operation of circuit breaker with covers on 70E

[TxEngr]

There?s a lot of discussion about the door open/ door closed operations and I don?t think the code is clear on this. It is clear as to the shock boundaries but not so clear on the arc flash boundary.

It is my understanding that the 70E Committee struggled with this for the 2009 edition with one segment wanting the rules to apply doors open and closed and the other segment feeling that the rules should apply doors open only. The final outcome was the addition of the FPN talking about how doors may not contain an arc flash. All of the calculations are based on open air or doors open so there is no calculation of a doors closed event.

So there are two questions: What is the requirement and what is safest? I?m still trying to get to the bottom of what the requirements are if you have done the arc flash study. I?m trying to contact some of the committee members to get an understanding of what they intended to say in the code. What is safest is a decision based on the minimum requirements, the design of your equipment and your company policies. Think of the insurance ad on TV these days with everyone in the car wearing crash helmets and the car filled with the plastic peanuts to protect everyone. It?s certainly safer to drive this way, but is it practical. It?s always a balance.

If anyone has any direct knowledge of the 2009 70E Committees discussions or a contact with the committee, send me a PM. Thanks.

 

[zog]

This issue about trying to read between the lines and what the intent of the commitee was is silly. I see the results of the aftermath of arc flash in equipment with the doors closed on a regular basis. Besides arc rated gear containment of an arc flash was never part of the design criteria, thats why every OEM's operation manual will have warnings of potential arc flash hazards.

Here is a recent example of an arc flash on a 480V with the doors closed, you think PPE would be a good idea?

 

[TxEngr]

If you read his original question he asks if the HC4 would be required in that case. There can be a big differenced in what's smart and what's required. In my plant, we have some 480V switchgear on the secondary side of a transformer that's rated extreme danger. We don't perform any operations on this eqipment energized - period. This means shutting down the machinery to do it which doesn't make our operations folks happy. But that's the way it has to be in our plant. Our evaluation of the hazard tells us to turn off the power - it doesn't matter if doors are open or closed. But that's a decsion we made about safety. Whether it's required or not I'm trying to determine.

 

[jim dungar]

Devices are designed and tested (i.e. UL)) to be used for switching on and off their continuous current rating plus a little bit (i.e. motor starting current). They are not intended to be operated, more than once, on high fault currents. So I can see some validity to a discussion that HRC>0 does not apply to the routine switching of small molded case circuit breakers on circuits know to be free from faults (i.e. there is a low risk of an incident occurring). To my knowledge the 70E committee has purposely tried to not get involved in all of the exact details of the employer's electrical safe work practices program. Each facility is unique in how they maintain and use their electrical system.

 

[zog]

If you read his original question he asks if the HC4 would be required in that case

And the answer is yes, if the calculated Ei for the panel requires HRC 4 PPE then thats what is required. No grey area here, there is no "derating" factor for covers on.

Now how they got HRC 4 on a 240V panel is beyond me, don't see that as a possibility unless they used >2 sec clearing time in the analysis.

 

[weressl]

There are several things that come into play including, construction of the equipment, presence of ventilating lovers, age and maintenance of the equipment, and most importantly the odds of a fault occurring.

Usually I tell my customers to suit up for the worst case incident energy. However I know that some molded case breaker manufacturers say that as long as the equipment being operated within its design parameters (i.e. not closing on a fault) it is UL tested to safely, without damage, interrupt normal load currents.

Following that logic how can you ever flick a lightswitch without being suited?

 

[weressl]

Several manufacturers state, that circuit breaker and enclosures contain internal breaker arcing, based on UL489 and UL891 normal continuous current ratings. They do not make this claim for fault current interruption.

The UL testing standards also requires fault interruption to be done safely. Obviously there is more venting of arc products in case of a fault.

 

[billsnuff]

don't they still make 'switch' rated breakers for lighting distribution?

 

[jim dungar]

Several manufacturers state, that circuit breaker and enclosures contain internal breaker arcing, based on UL489 and UL891 normal continuous current ratings. They do not make this claim for fault current interruption.

The UL testing standards also requires fault interruption to be done safely. Obviously there is more venting of arc products in case of a fault.

UL requires (1) open-close-open cycle at full fault current, after that the breaker is allowed to 'fail'. So how many operations are allowed at in the instantaneous region of the breaker?

 

[jim dungar]

don't they still make 'switch' rated breakers for lighting distribution?

The fact that breakers are designed for switching does not address the amount of PPE required to operate them.

 

[weressl]

Several manufacturers state, that circuit breaker and enclosures contain internal breaker arcing, based on UL489 and UL891 normal continuous current ratings. They do not make this claim for fault current interruption.
UL requires (1) open-close-open cycle at full fault current, after that the breaker is allowed to 'fail'. So how many operations are allowed at in the instantaneous region of the breaker?

You are changing the premise of my statement and bringing in another aspect.

 

[billsnuff]

"So I can see some validity to a discussion that HRC>0 does not apply to the routine switching of small molded case circuit breakers on circuits know to be free from faults (i.e. there is a low risk of an incident occurring). "

Jim,

actually i was agreeing with the above. my 'puter won't let me use the site functions for some reason. just know we resolved most of our lighting panel problems with balancing loads and lowering fuse amperage, and in one instance, we replaced the panel (stabs were shot) and spec'd SW rated breakers for lighting loads (weekend shut down).

As far as PPE do what the study or label says until you can mitigate the hazard. Aren't reccomendations usually included in the Arc Flash Study?
I'm still curious ar to why his is HRC#4, if in fact it is.

 

[jim dungar]

SW rated breakers for lighting loads (weekend shut down).

I often perform studies where the 208V equipment has high incident energy, especially when the transformer is larger than 225kVA. the problem is compounded by having the 'main' protection in the same enclosure as the branch breakers. SWD rated breakers do nothing for mitigating a potential arc flash. You are still left with the OP question of what PPE is required.

The 'task tables' of 70E result in a Hazard RISK Category. Calculations only result in a hazard. There are FPN and appendices to 70E that infer risk should be evaluated in some circumstances.

If your analysis generates an incident energy of 8.3 cal/cm?, what PPE is actually needed? Most people simplify their PPE selection by equating the incident energy hazard from a study with the maximum energy levels for HRC's which come from the task table, but 70E does not require them to do so. Some companies (mine included) take this a step further and only use two levels of PPE, HRC=2 and HRC=4, which can mean you are dressing up in 40 cal/cm? clothing to switch a breaker mounted in a panelboard with 8.3 cal/cm? available.