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 Post subject: PPE for equipment operating at less than 50 V
PostPosted: Mon Sep 12, 2016 11:10 am 
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Joined: Sat Apr 04, 2009 9:50 pm
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Location: San Antonio, TX
Is there any requirement in the NFPA 70E 2015 regarding PPE for maintaining equipment of less than 50V?


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 Post subject: Re: PPE for equipment operating at less than 50 V
PostPosted: Tue Sep 13, 2016 3:51 am 
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Location: Rutland, VT
I don''t believe there is but it would still be prudent for personnel to wear non-flammable clothing and eye protection.

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 Post subject: Re: PPE for equipment operating at less than 50 V
PostPosted: Sat Sep 17, 2016 5:01 am 
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70E is very annoying on this point. Effectively the way that the Code is written, there is no guidance at all for 50 V or less cases either from a shock or an arc flash perspective. In other words, you are on your own since you are working outside the Code's scope. If you read the shock section very carefully it suggests that there is probably not a hazard but then states that the end usr must actually determine whether or not a hazard exists. In other words, no guidance. In terms of arc flash hazards it never gives a lower bound at all. In other words, no guidance.

That being said, MOST regulatory jurisdictions state that there is no shock hazard below 50 VAC and are silent on DC. An exception for example is New Brunswick province in Canada that gives a strange 28 VAC lower cutoff, which makes working on Ethernet (48 V POE), telephone systems (48 VAC ringers), and even most USB cables now treated as a shock hazard, something that is ridiculous. Similarly there is experimental evidence that suggests that there is something of a threshold somewhere around 150-250 VAC where arc flash ceases to become a major hazard simply because self-sustaining arcs are no longer possible but the precise threshold hasn't been given by any standard yet. Not only that but the existing arc flash models assume that the arc is stable and self-sustaining and thus are totally inapplicable to non-self sustaining arcs.

Regulatory jurisdictions only require you to address RECOGNIZED hazards and that means that not only is the phenomenon well documented in scientific and engineering literature but methods to avoid it are documented and that the risk is significant. So when you go out of scope of the consensus safety standards, that puts it in a category of no longer being recognized. Thus for instance prior to around the 1990's arc flash was not a recognized hazard...we knew it existed but it was still under study without the benefit of any kind of way of predicting it (Lee model was developed in the 1990's). At that time there were work practices (don't work energized if you don't have to, stand to the side of the breaker) but that's about it.


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 Post subject: Re: PPE for equipment operating at less than 50 V
PostPosted: Sat Sep 17, 2016 6:22 am 
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Location: San Antonio, TX
Thanks. Very clear.


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