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 Post subject: NFPA 70E, Table 130.5(C) Likelihood ... first time after ..
PostPosted: Mon Sep 06, 2021 4:57 pm 
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Joined: Thu Oct 30, 2014 11:07 am
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Location: Ohio
In Table 103.5(C) Estimate of the Likelihood of Occurrence of an Arc Flash Indecent for ac and dc Systems it lists the "Operation of a CB or switch the first time after installation or completion of maintenance in the equipment." as having a likelihood of occurrence. Would this be inclusive of the first time a 20 ampere 277 volt 1-pole toggle switch (light switch) is operated?


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 Post subject: Re: NFPA 70E, Table 130.5(C) Likelihood ... first time after
PostPosted: Tue Sep 07, 2021 12:58 pm 
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Joined: Thu Apr 18, 2019 11:42 am
Posts: 59
I'd say yes...infant mortality. Likelihood though is low. You might reference IEEE 493.

Mike


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 Post subject: Re: NFPA 70E, Table 130.5(C) Likelihood ... first time after
PostPosted: Wed Sep 08, 2021 9:14 am 
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Joined: Mon Jan 18, 2010 11:35 am
Posts: 547
Location: Wisconsin
mpparent wrote:
I'd say yes...infant mortality. Likelihood though is low. You might reference IEEE 493.


It's not just infant mortality, in many cases until energization is the first time the circuit is 'checked' for wiring errors like short circuits.


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 Post subject: Re: NFPA 70E, Table 130.5(C) Likelihood ... first time after
PostPosted: Mon Sep 13, 2021 7:20 am 
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That table name cannot be correct. Spell check strikes again.


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 Post subject: Re: NFPA 70E, Table 130.5(C) Likelihood ... first time after
PostPosted: Tue Oct 05, 2021 8:18 am 

Joined: Mon Apr 29, 2019 5:24 pm
Posts: 21
Location: Phoenix, AZ USA
Are you speaking of manipulating a single pole 277V "switch rated" (SWD or HID) miniature circuit breaker (MCB) mounted in a panelboard or switchboard or are you referring to a standard wall mounted 277V toggle switch used for room lighting?

If the toggle switch, I'd say no because its a branch circuit downstream from the OCPD feeding it, so the available fault current would be limited by the small OCPD.

However, if the single pole MCB, and it's "switch rated" (SWD or HID), then I'd would default to a conservative position because I've seen several MCBs fail in my experience. Also the available fault current would originate from it's line side bus connection which could be protected by a large main breaker located in the same panel or a breaker installed in a completely different panel.

But if the single pole MCB is NOT switch rated then this is not a good safety practice regardless of Table 130.5(C) because it's not designed for this application and in doing so violates 70E Article 110.4(D)(3) and OSHA 1910.303(b)(3).


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 Post subject: Re: NFPA 70E, Table 130.5(C) Likelihood ... first time after
PostPosted: Mon Oct 18, 2021 1:43 pm 
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Joined: Sat Nov 21, 2009 10:23 pm
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Location: Ohio
JBD wrote:
mpparent wrote:
I'd say yes...infant mortality. Likelihood though is low. You might reference IEEE 493.


It's not just infant mortality, in many cases until energization is the first time the circuit is 'checked' for wiring errors like short circuits.


I am with you, I did an OSHA investigation where the incident resulted in a death. An electrician installed a Size#4 two speed starter, it was wired incorrectly, he did not close the MCC door, his burns were minor, however, he passed from a resultant staff infection.

As far as small ampacity circuit breakers, you seldom see them near the service entrance, therefore, the IE is going to typically be under 1.2 cal/sqcm. down stream of the breaker. However, if the fault current is high and the breaker AIR is under-rated , that presents a problem. Any device located at a 480V service entrance (or large kVA substation) is subject to closer scrutiny.


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