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 Post subject: Switchgear Metering Compartments
PostPosted: Wed Sep 16, 2009 8:28 am 

Joined: Wed Sep 16, 2009 7:55 am
Posts: 2
I have been asked by my customer to provide individual labels on our low voltage switchgear compartments. Since all of the feeder breaker compartments have the same label, what about the metering compartments? Are the same arc flash hazards present at this compartment as the individual breaker compartment? What about the possibility of arc flash hazards on opening a CT circuit?


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PostPosted: Wed Sep 16, 2009 11:23 am 
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Joined: Mon Jun 02, 2008 11:58 am
Posts: 1103
Location: Charlotte, NC
ronmwilliams wrote:
I have been asked by my customer to provide individual labels on our low voltage switchgear compartments. Since all of the feeder breaker compartments have the same label, what about the metering compartments? Are the same arc flash hazards present at this compartment as the individual breaker compartment?


Yes and no, the hazard may be reduced in the metering compartment but there is no way to calculate that so you should label them the same if you did an analysis.

ronmwilliams wrote:

What about the possibility of arc flash hazards on opening a CT circuit?


CT's should never be open circuited. ever. But if they were, it would be a fizz. pop. smoke, kind of thing, not a be burn causing arc flash.


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PostPosted: Wed Sep 16, 2009 11:23 am 
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Joined: Mon Jun 02, 2008 11:58 am
Posts: 1103
Location: Charlotte, NC
ronmwilliams wrote:
I have been asked by my customer to provide individual labels on our low voltage switchgear compartments. Since all of the feeder breaker compartments have the same label, what about the metering compartments? Are the same arc flash hazards present at this compartment as the individual breaker compartment?


Yes and no, the hazard may be reduced in the metering compartment but there is no way to calculate that so you should label them the same if you did an analysis.

ronmwilliams wrote:

What about the possibility of arc flash hazards on opening a CT circuit?


CT's should never be open circuited, ever. But if they were, it would be a fizz. pop. smoke, kind of thing, not a big burn causing arc flash.


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PostPosted: Thu Sep 17, 2009 12:05 am 
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Joined: Sun Dec 23, 2007 1:44 pm
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Location: Charlotte, NC
I would think that if you are using PT's (no bus voltage brought into the compartment) for the voltage portion of the metering the arc flash issue does not exist, especially if it is a 120 volt secondary. If the metering voltages are tapped directly from the bus, then you most likely still do have an issue.

Alan


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PostPosted: Wed Mar 10, 2010 8:58 am 

Joined: Wed Mar 10, 2010 8:43 am
Posts: 1
Location: SC
Why not treat as a wired load?

I believe this should be treated as a wired load:

- perform short circuit study through existing wires from the bus using lenth, available Isc, etc.
- determine load Isc
- perform arc flash calculation


This seems a much more reasonable approach.

Has anyone ever heard of an arc flash event at an instrument cabinet??


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