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 Post subject: Remote Racking
PostPosted: Wed Mar 17, 2010 6:45 am 
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Sparks Level

Joined: Wed May 13, 2009 3:19 pm
Posts: 56
This topic has been debated several times already but I though was worth bringing it up again; maybe there are some new members with new opinions on the subject.

We continue to have problems with not only trying to explain to others but in convincing our selves there’s an arc flash hazard at remote racking distances (20 – 25 feet). We agree there are some possible hazards associated with flying debris but we are not convinced there’s an actual burn hazard at these distances. Most switchgear remote racking takes place doors closed with the operator standing at some off angle with respect to the breaker cubical. In some cases the control cord does not always move them out of the calculated flash boundary. As most are aware of the IEEE equations can produce some truly unbelievable flash protection distances. We know vendors are offering wireless options with hundreds of feet of range or you can add additional cable but is this truly needed?

How are you discussing this issue with your sites and clients? If you calculate HRC 4 at 24” or 36” do you tell them they need HRC 4 PPE at 25 feet if the FPB is beyond 25 feet? Do you tell them they still need arc flash PPE at 25 feet but it can be less than the 24” or 36” value? If so, how are you determining this lesser value? We’ve tried setting the working distance to the control cable length and recalculating the incident energy at this distance but we feel the results are overly conservative and not valid.


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PostPosted: Wed Mar 17, 2010 7:35 am 
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Joined: Mon Jun 02, 2008 11:58 am
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Location: Charlotte, NC
The whole point of remote racking is to eliminate the need for PPE so doing the operations outside the AFB is desirable, even if it may be conservative.


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PostPosted: Mon Mar 22, 2010 1:44 pm 
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Joined: Wed May 13, 2009 3:19 pm
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According to the 1584 standard the distance factor (x) was developed based on test data out to 60” – 72”. The question is what’s the assumed accuracy of the model beyond these distances? One could argue the model is only accurate to calculate incident energy values and flash boundaries out to 72” at best.


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PostPosted: Mon Mar 22, 2010 2:11 pm 
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Joined: Mon Jun 02, 2008 11:58 am
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Location: Charlotte, NC
SCGEng1 wrote:
According to the 1584 standard the distance factor (x) was developed based on test data out to 60” – 72”. The question is what’s the assumed accuracy of the model beyond these distances? One could argue the model is only accurate to calculate incident energy values and flash boundaries out to 72” at best.


Too many variables I would think, what about that 50/51 relay flying at your head at 500 MPH?


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