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 Post subject: Nominal Voltage
PostPosted: Thu Feb 08, 2018 8:34 am 
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We are trying to determine what the nominal voltage of an industrial control panel is, as per OSHA, NFPA, and what is the safe thing for our employees. Diving deep into the technical language of NFPA 70E, has left us into two camps and need some clarification as to where to draw the line. We are using the 2018 version.
We have a typical industrial control panel powered by a 120 Volt, 15 amp, 1 phase, 3 conductors (L1, N, & G ) circuit. The source of the power is a 120/ 208 distribution panel. The question is what voltage to use when determining the nominal voltage of the panel so that the correct PPE and boundaries may be determined.

NFPA 70E definition is:
Voltage, Nominal. A nominal value assigned to a circuit or
system for the purpose of conveniently designating its voltage
class (e.g., 120/240 volts, 480Y/277 volts, 600 volts). [70:100]

Table 130.4(D)(a) use “Nominal System Voltage Range, phase to phase”
Table 130 .5(C) uses “Nominal XXX Volts”

Do we use the value assigned to the circuit, and follow the PPE requirements for 120 volts?
Or do we use the maximum system voltage and follow the PPE requirements for 208 volts, since the source has potential of providing 208 volts?

Does anybody know of any clarification from either OSHA or NFPA about where to draw the line when determining the nominal system voltage?

Looking forward to the discussion.


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 Post subject: Re: Nominal Voltage
PostPosted: Thu Feb 08, 2018 9:50 am 
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Location: Rutland, VT
If the panel has only 120V to it, that is your nominal voltage for PPE. Since 208V is not carried to that panel, the 208V does not exist in that panel. The panel the 208V is at, 208V is the nominal voltage.

I think overall, there is very little difference in shock PPE for either situation. The gloves are going to be a minimum of Class 0 (500V) and the only difference is in the Restricted Approach Boundary.

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 Post subject: Re: Nominal Voltage
PostPosted: Fri Feb 09, 2018 10:49 am 
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Thanks for the reply, The big difference is do you need ARC FLASH PPE. There is a cutoff at 125 VAC/DC in table 130.5.(C)

When using Table 130.5(C) 2018 to decided if you have a like hood of an occurrence of an arc flash when testing and troubleshooting a 120 VAC control panel, the first group of tasks listed in the table with " Working on control circuits with exposed energized conductors ..., nominal 125 Volts as or dc or below .. without any other exposed energized equipment over nominal 125 volts" lists the like hood of occurrence as No.

This would lead me to say testing 120VAC circuit would not require a full face shield and other ARC Flash gear, though PPE for Shock (Gloves) is still required.


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 Post subject: Re: Nominal Voltage
PostPosted: Fri Feb 09, 2018 6:33 pm 
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If you only bring in one phase it's 120 V because it's fed phase to neutral. At the service panel you have all 3 phases which would be 208. I can't imagine a fault inducing 120 V of another phase on a solidly grounded neutral which it would be by Code.


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