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 Post subject: Arc Flash Label/CalculationPosted: Wed Apr 17, 2024 6:16 am

Joined: Thu Mar 21, 2024 6:08 am
Posts: 6
Greetings! I'm relatively new to the safety world. I worked safety while in the service but nothing like this. I'm looking at our NFPA70E processes/programs. I understand that our disconnects with arc flash potential require the appropriate label. Our company sent in an engineering student (intern) to hash out out 70E process. He did just that about 15 years ago. He created nice labels that contained of the required info. Here's my problem, I am trash at math. It was never my strong suit. I have to replace a few stickers but I have no way of getting the calculations run. We currently have have 2 situations where a series of boxes share the exact same wiring but the , labeled "boundaries" are different,

Question:
Can I use the over all voltage and make PPE decisions that way?

How would you handle this?

Phil

PS ...I cheated in math while at college ..

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 Post subject: Re: Arc Flash Label/CalculationPosted: Wed Apr 17, 2024 6:25 am
 Sparks Level

Joined: Thu Apr 18, 2019 11:42 am
Posts: 112
Sounds like you need an updated study...the calculation methodology has changed since 15 yrs ago. As an interim, you could use the table method in 70E, but you have to be very cognizant of the limitations and footnote boundaries for its use.

Mike

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 Post subject: Re: Arc Flash Label/CalculationPosted: Wed Apr 17, 2024 6:40 am

Joined: Thu Mar 21, 2024 6:08 am
Posts: 6
[ Are you referring to the AC voltage 130(C)(15)(a) and the DC voltage 130.(C)(15)(b)?

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 Post subject: Re: Arc Flash Label/CalculationPosted: Wed Apr 17, 2024 8:50 am
 Sparks Level

Joined: Fri Jul 08, 2016 10:01 am
Posts: 319
Location: Indiana
Pretty much what Mike said.

To use the table method you need to know and understand what fault current and clearing time means.

Where are you located? There are probably some members on here that can give you a proposal on performing a study and labeling.

_________________
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PE in 16 states

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 Post subject: Re: Arc Flash Label/CalculationPosted: Wed Apr 17, 2024 9:01 am

Joined: Thu Mar 21, 2024 6:08 am
Posts: 6
bbaumer wrote:
Pretty much what Mike said.

To use the table method you need to know and understand what fault current and clearing time means.

Where are you located? There are probably some members on here that can give you a proposal on performing a study and labeling.

I'm in Georgia. The tables you are referencing are the ones I cited above?

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 Post subject: Re: Arc Flash Label/CalculationPosted: Wed Apr 17, 2024 2:04 pm
 Sparks Level

Joined: Thu Apr 18, 2019 11:42 am
Posts: 112
Philip.camp wrote:
[ Are you referring to the AC voltage 130(C)(15)(a) and the DC voltage 130.(C)(15)(b)?

Those tables are what we call the "table method". To reiterate, there are very specific limitations listed in the footnotes. Also, via this procedure, PPE is selected via table 130.7(C)(15)(c).

Mike

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