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 Post subject: Age Considerations for Equipment Operation
PostPosted: Wed Sep 11, 2013 8:59 am 

Joined: Fri May 10, 2013 5:40 am
Posts: 3
I am an engineer conducting an arc flash/coordination/short-circuit study for a health care facility. The hospital service entrance system consists of a 4.16kV fuse-switch line up with a preferred reserve utility configuration. This equipment has remained unchanged since the installation in 1978. (Not sure if the switches have even been operated) Using the SKM modeling system and the available fault of roughly 1.6kA 3ph symmetrical from the utility, the resultant PPE level for this equipment is Level 1. Given the age of this system and the possibility of a switch sticking or a faulty fuse is Level 1 still appropriate?


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PostPosted: Thu Sep 12, 2013 4:23 pm 
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Joined: Tue Oct 26, 2010 9:08 am
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Location: North Carolina
Three issues.

1. The PPE levels only apply when using tables. If you do your own calcs, you cannot use the PPE table "backwards". Annex O states this.

2. Fuses can fail but this is rare. When they are out of tolerance it is almost always tripping early/low. If they pass NFPA 70B inspection criteria (see article 2xx of 70B) they are probably good. Either way the impact on incident energy is that it may be conservative with fuses. So no, don't "derate".

3. Switches typically fail by hidden failure that is revealed during use. As described it is likely to be nonoperational and fails to meet article 200 (properly maintained) so the risk of an arcing fault, however small with a switch (they rarely fail this way...see ieee 493) is elevated so PPE is warranted while operating it. For under 4 cal, this is just standard industrial attire plus fr shirt/pants or fr coveralls.


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