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 Post subject: Replacement 70E equipment tables
PostPosted: Tue Dec 09, 2014 10:43 am 
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Location: North Carolina
This table is based on running the 70E calculation at the given working distance with an assumed arcing time of 2 seconds.

Equipment Type System Voltage kA for 1.2 cal/cm2 kA for 4 cal/cm2
Open Air 480-600 0.15 0.5
1-15 kV 0.1 0.3
Switchgear 480-600 0.1 0.4
1-15 kV 0.1 0.3
MCC’s and panelboards
480-600 0.07 0.25

Maximum short circuit current is easily calculated unlike trip time so it is possible to use this table to calculate incident energy knowing only short circuit current and where clearing time is immaterial (vis a vis the "2 second rule"). Unfortunately it should also be clear that the available fault current is extremely low using this methodology.


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 Post subject: Re: Replacement 70E equipment tables
PostPosted: Tue Dec 09, 2014 1:43 pm 
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Can you please cite which table you are specifically referring to in NFPA 70E-2015?

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Barry Donovan, P.E.
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 Post subject: Re: Replacement 70E equipment tables
PostPosted: Wed Dec 10, 2014 1:42 pm 
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Specifically the equipment tables. The "equipment types" though that I am using are based on the working distance/exponent tables from IEEE 1584 so there is not a 1:1 correspondence. 70E gives an equipment type, a maximum short circuit current, AND a maximum trip time. The issue with this is that once you determine trip time, the table is useless because you can just as easily plug the rest of the parameters into IEEE 1584 and skip the equipment tables...basically calculate incident energy.

This table simplifies this problem by eliminating trip time as a parameter. Unfortunately the consequence of eliminating it (drive opening time to 2 seconds) is that the maximum short circuit current becomes very limited. I haven't extended the tables out to "PPE 4" yet. Doing so will moderately increase the fault current limitations.


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