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 Post subject: Finger-Safe Guards
PostPosted: Thu Sep 18, 2008 12:39 pm 
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Joined: Thu Sep 18, 2008 12:35 pm
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Does adding Finger-Safe guards to a panel reduce the Arc Flash hazard?
ie. Putting plexiglass ove all exposed 480 vac connections.


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PostPosted: Thu Nov 13, 2008 10:15 am 
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Location: Michigan
We have been recently debating that too; unfortunately I don't have a solid answer and can only offer the conclusion that most of us where I work seemed to have arrived at.

I believe finger-safe guards designed to prevent electric shock due to direct contact ultimately help prevent arc flash events from occuring (ie. dropped tool ect.).
I don't believe the guard could contain the blast or reduce the incident energy level however it may prevent the incident from happening in the first place. In the event that an arc flash actually does occur, that finger-safe guard probably does not have an ATPV rating and therefore is just one more material present in the arc blast.

So the question remains, to guard or not to guard? I would use the covers but not consider them a safety factor when determining the arc flash hazard unless they are listed for that purpose by the manufacturer.


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PostPosted: Mon Nov 17, 2008 9:35 am 
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jonp20001 wrote:
Does adding Finger-Safe guards to a panel reduce the Arc Flash hazard?
ie. Putting plexiglass over all exposed 480 vac connections.


Assuming the plexiglass is voltage rated, that would be one way to reduce the approach distances (not arc flash exposure) cited in NFPA 70E. This is a legitimate concern (and benefit) because control system work often encroaches on the these approach boundaries for 480V. Barriers might allow a person to work on low voltage control wiring in a cell without needing the precautions of Restricted or Prohibited 480V approach boundary work.

The prescriptive Arc Flash PPE table in NFPA70E recognizes similar reduction in probable contact, with lower prescribed PPE not based on calculated exposure. That is testamony to safety improvements such barriers would achieve though there is no method given for applying this to the calculated exposure.


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