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 Post subject: Operating Breakers with High Incident Energy
PostPosted: Tue Mar 15, 2011 8:34 am 
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Joined: Tue Mar 15, 2011 8:13 am
Posts: 1
First of all let me say, please be merciful this is my first post.

I have a question regarding operating and racking in and operating breakers on low voltage switchgear that has high incident energy at the breaker.

The specific case involves a piece of ABB ATLV MaxSG Metal Enclosed Switchgear running at 480V. The switchgear has a 22 cal/cm2 incident energy at the bus per my current calculations. This energy is calculated using the switchgear main breaker as the fault clearing device.

However, the gear has a very large incident energy on the line side of the mains, this is because the clearing device for that point is up at the 13.8kV level. The incident energy is above the level that any arcflash gear would allow a worker to do live work on the device.

The question is, does this large amount of energy prohibit a person from
a) racking in or racking out the main breaker while the line side is live
b) opening or closing the breaker using the controls mounted at the gear

Please provide a code or standard reference with your response, these could be IEEE, NFPA, API or any other standards setting body, or even (less desirable) an equipment manufacturer publication. It is ok if your reference is "reaching" as to what it is really saying, I am just looking for anything to put me on more solid ground with this.

I was under the impression that the hazard category for metal enclosed switchgear would basically determine what equipment would have to be worn once the front door of the gear was open, and would certainly not affect "b" above but would affect "a" once you reach the point of racking where the door has to be open. I am having trouble justifying my position and so would be interested in hearing any references about this matter.

Thank you,

Micah


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PostPosted: Tue Mar 22, 2011 6:34 am 
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Joined: Thu Oct 14, 2010 8:04 am
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for racking in/out it will most definitely apply because that would constitute as energized work. however operating handles has been suggested to me as energized work as well.

From my understanding, faults, or even breaker failures, are to be taken in consideration and the amount of incident energy calculated is available regardless of what the person may be doing. Even with the door closed, faults can blast molten copper straight through the metal clad switchgear.

I wish there were more hardfast codes/definitions on this subject. It causes alot of practicality vs safety discussions in my office as well. But the bottom line is safety when my life is on the line, so why not impliment it for respect of other humans as well.

Others please chime in, I am not an expert. and have a similar situation in question my self: 400A 480V Main Service Disconnect (Fused switch) is calculated to have "Extreme Danger", would proper recommendations be to have the utility shut down power as opposed to plant personell operating the switch, until the "Extreme Danger" is remedied? Is that energized work?

(not to thread hijack, just to offer similar scenarios that may bring up different views/opinions about the same topic).

-HF


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PostPosted: Fri Apr 08, 2011 5:48 am 
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Joined: Fri Apr 08, 2011 5:02 am
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Task Matrix Table 130.7.c.9 in 70E identifies the task of operating a disconnect in a 600V MCC, with the door closed, as a Cat#0 task (requiring Cat#0 PPE). This determination was based on a risk assessment that the 70E committee members agreed apon that gave a 3 category reduction from the calculated MCC Cat#. This risk assessment was based on the fact that this task was deemed an "extremely low risk" task. (This risk assessment was documented in the 70E-2003 Pre-print, Annex J, but not included in the final 2004 issue.)

The committee was therefore telling us (reading between the lines) that the bucket door, along with correct operating procedures, are relevant in reducing the risk but not to to the point of completely eliminating it.


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