Arc Fault

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mshields

mshields

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Boston, MA
We just received an arc fault study from Cutler Hammer in which they rate the level of risk from 1 to 4 and a 5th category "dangerous". 1 thru 4 refer, presumably, to the level of PPE equipment required (or at least I assume as much). I assume ?dangerous? means there is no level of PPE that will make working on it acceptable. True?

If the above is correct, what can be done about the devices that are deemed ?dangerous?. It seems to me that the only thing you could do is dial down the instantaneous to a level that you forgo a degree of selectivity in favor of the safety concern.

True? Are there any other options?

Equipment is already installed so we can?t go with fancy breakers that lower the Instantaneous when someone is in close proximity or for that matter change out any other equipment.

I have put these questions to Cutler Hammer but knew I could count on this crowd to have valuable input.

Much appreciated!

Mike
 
You need to attend a class on NFPA 70E. NFPA 70E is about creating an electrical safe workplace. It is an ongoing process, it is not just a project of installing labels and buying PPE.

The way to deal with Dangerous locations is to absolutely not work on them while they are energized. The standard work distance for Arc Flash calculations at 480V is 18", so when voltage testing some of these 480V Dangerous locations use tools that move you further away than 18" (i.e. a "hot stick"); and of course you will first need to rerun your calculations using the new working distance.
 
There are after market systems that can be installed. One that works very well is the fiber optic detection system from ABB. Another alternative is to install a switch that enables the instantaneous function (set as low as possible) if needing to work hot. You can also add high speed bus differential relaying, or like Jim said, simply don't work live on that equipment.

Arc Flash studies run once, IMO do not meet the intent of NFPA70E, especially if switching configurations can change that alter the fault/arc fault current. I believe this is a big misconception being perpetuated by individuals trying to capitalize on the market who do not really understand what it takes.
 
This is a stretch, but is bus differential relaying feasible? This is another way of limiting arc flash hazard without sacrificing selectivity.
 
We had an arc-flash, breaker coordination, and AIC study done on our facility. The firm that did our study also provided recommendations on how to bring the Hazard Risk Category (HRC) down to a lower level, how to take care of AIC problems, and what to change for coordination. IMO Cutler Hammer should do the same for you, or at least tell you if there's nothing you can do.

If it's a Dangerous HRC, then it's a NO-GO.

But the Info they provide is useless unless you've been trained on how to interpret the info and know how to work safely in accordance with NFPA 70E.
 
Sharpie said:
The firm that did our study also provided recommendations on how to bring the Hazard Risk Category (HRC) down to a lower level, how to take care of AIC problems, and what to change for coordination.
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Good for you.

Many projects that I bid do not find recommendations to be of value. They want the lowest cost "labels" they can get. I know of several firms where mitigation suggestions are listed as a cost adder if they are quoted at all. It is not unusual for me to get requests to make recommendations based on studies done by other companies. All arc flash studies are not equal, I know of one case where our study bid was $100K and a competitor was at only $9,600 (yes $9,600).
 
jim dungar said:
I know of one case where our study bid was $100K and a competitor was at only $9,600 (yes $9,600).
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I bet it was some guy using the bussmann or duke freeware programs and has no idea what he is doing. I have bid against those types also, I would think that type of price difference would set off alarms for the customer. Then, again, if they want cheap and easy, I dont want to waste my time.
 
Just like keeping one-lines up to date, and doing proper O&M, Owners see arc flash as a necessary evil. The responsibility to get it done usually falls on the Safety person. Unfortunately, most are not well versed on the subject and simply want to be able to tell their boss they got it done within some limited budget (unrealistic, that is).

Ironically, utilities and power generation facilities are not much better. When we do a proposal, we tell the Owner that this is not a one time thing, that the system needs to be kept up to date. We then put in the cost for a standalone copy of the program, and training to use it. Some see the value, and we usually get those jobs; others just want a cheap price, and will go for the $5k worthless study by somebody else. We won't do the cheapo study.
 
At the plant I work at we have level 5 or dangerous breakers. Most of ours are 800A feeding MCCs. We cannot open or close them while they are energized. The transformers feeding these breakers are only considered class 1, so to open or close the breakers we have to open the transformer first.
 
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