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 Post subject: Switchgear non-powered compartments
PostPosted: Mon Sep 29, 2014 5:29 am 
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Location: Port Huron, Michigan
The specific question I have is regarding 600V switchgear, but it most likely would apply to any. Each switchgear assembly includes a main breaker, various numbers of feeder breakers, a metering compartment, and an empty (storage) compartment. The metering compartment and empty compartment do not have direct access to the bus. What should the incident energy be for these compartments? Intuitively, I feel like you should be able to open those compartments up without arc flash protection.


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 Post subject: Re: Switchgear non-powered compartments
PostPosted: Mon Sep 29, 2014 10:51 am 
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Location: North Carolina
Is it likely to cause an arcing fault?

As a counter example, there is a case out there where some workers were working on a section of an MCC and just from the vibration of the work that was being done, initiated an arc flash which caused injury to a second set of workers that were working near the same MCC but in front of a completely different section. Similarly it is entirely possible, and with MCC's frequently happens, that an arc initiated in one section on the bus travels down the bus via magnetic propulsion and then the flash appears at a completely different spot farther away from the source.

As you can see from these two examples, it is possible to extrapolate the "what if's" to the point where all natural catastrophes from tornadoes to earthquakes to tsunami's to meteor strikes would render any and all electrical work a hazard just by being present in the vicinity of electrical equipment.

Juxtapose this with the comment often repeated by the NFPA 70E Committee that "just walking by" is not an arc flash hazard. Or to rephrase using modern terminology (that used in 70E-2015), just walking by is not an arc flash RISK, or more specifically, it is an acceptable risk. All activities carry some inherent risk. The question is whether or not it is an acceptable or tolerable one.

And to that end, 70E talks about whether or not the task is likely to initiate an arcing fault. Based on what you describe depending on what you are doing, it might. For isntance if you are going to pull those buckets off the bus or reinsert them might be a very different situation from opening the door and take some measurements.

I'm going to answer your question now, by not answering it. The issue though is that risk is industry, country, and entity-specific. It depends on the risk tolerance of your specific organization. Generally for fatalities these fall between around 1 in 1 million and 1 in 10 million. Arc flash major injuries requiring hospitalization run at around 1 in 100,000 on average with fatalities running between 1/10th and 1/20th of that rate. That puts the overall risk at the tolerable level for most tasks. The question then becomes what your organization's risk is and whether the task exceeds this level or not. There's no easy answer here but I'll give you a hint. Operating breakers and disconnects under non-fault conditions where a quick visual inspection does not indicate a major safety concern as per the 70E-2015 standard would be acceptable without PPE. What you are describing is a lower risk than this.


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