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Do you consider operating a CB or switch the 1st time as an increased likelihood of an arc flash?
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 Post subject: Operate CB or switch for first time - Arc Flash Hazard?
PostPosted: Sun Jun 28, 2020 8:37 am 
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Location: Scottsdale, Arizona
The 2021 Edition of NFPA 70E has many changes.

One change is the new addition to Table 130.5(C) Estimate of the Likelihood of Occurrence of an Arc Flash Incident for ac and dc Systems.

A new task was added “Operation of a CB or switch the first time after installation or completion of maintenance in the equipment.” This new addition is identified as “YES” for likelihood of an arc flash incident for any condition – including normal operation.

Here is this week’s question:

Do you consider operating a CB or switch for the 1st time after installation (or after maintenance) an increased likelihood of an arc flash?

Yes
No
It Depends

What are your thoughts about this new addition?


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 Post subject: Re: Operate CB or switch for first time - Arc Flash Hazard?
PostPosted: Mon Jun 29, 2020 3:52 pm 
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Way back in my engineering coop student days in the late 1970's, I worked at a large cast iron foundry near my hometown in Ohio.

I recall a few of their electricians believed in the "smoke theory of electricity" (do a web search, it is really out there so it must be true! :o ).

Basically everything is powered by smoke and if you see smoke escape from the circuit, that is an indication that the circuit failed. Their way of testing a circuit was give it a quick visual and then throw the switch. That is when I also saw my first arc flash as underdutied equipment exploded (another issue).

In hind sight, maybe that is why I gravitated towards arc flash. This task appears to be a welcome addition to the 2021 Edition to NFPA 70E Table 130.5(C)!


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 Post subject: Re: Operate CB or switch for first time - Arc Flash Hazard?
PostPosted: Mon Jun 29, 2020 7:38 pm 

Joined: Fri Aug 22, 2014 2:31 pm
Posts: 6
I'm assuming that there is a concern that, after the maintenance activity, a foreign object was left in the breaker, or an essential component was left uninstalled, and that the initial operation of the breaker results in this item (or lack of item) causing a fault? I was curious if there have been multiple instances where this has happened in industry? We have several MV and LV air CBs at our facility and I haven't experienced this happening.


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 Post subject: Re: Operate CB or switch for first time - Arc Flash Hazard?
PostPosted: Tue Jun 30, 2020 6:36 am 
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rn70410 wrote:
I'm assuming that there is a concern that, after the maintenance activity, a foreign object was left in the breaker, or an essential component was left uninstalled, and that the initial operation of the breaker results in this item (or lack of item) causing a fault? I was curious if there have been multiple instances where this has happened in industry? We have several MV and LV air CBs at our facility and I haven't experienced this happening.


Thanks for your comment! Exactly what we are looking for - various views. The case that I mentioned was over 4 decades ago and was mostly due to poor practices which should not (?) exist in today's environment. I don't know how common of an experience this is with everyone but it would be great to hear the experiences of others as well.

Thanks rn70410!


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 Post subject: Re: Operate CB or switch for first time - Arc Flash Hazard?
PostPosted: Wed Jul 01, 2020 4:52 am 

Joined: Fri Jan 31, 2020 1:51 am
Posts: 1
I think this addition makes a lot of sense, especially on return to service after maintenance.

In my industry we are now seeing gaps of 4 or 5 years between routine maintenance on switchgear and pressure to push these gaps out even further if possible. This means each time it is completed, the task is less routine and less familiar to those carrying it out and so there is more opportunity for mistakes to be made, steps to be missed etc.

As an example I have come across the situation where the breaker racking mechanism needs to be carefully maneuvered at a certain point of travel to clear a catch. As people do the task less often they do not know the "trick" and end up forcing the mechanism which can lead to misalignment, damage and the increased potential for an arc event when the switch is closed. I think it is good to draw attention to the increased risk in this situation, with the caveat that we also try and improve procedure/job step plans.


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