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ekstra   ara
 Post subject: 120VAC control panel labeling
PostPosted: Thu Feb 14, 2019 7:02 pm 

Joined: Thu Feb 14, 2019 6:57 pm
Posts: 1
Hi,

With the 208VAC , 125KVA exemption removed from the IEEE 1584, how would you do the IE or even label a 120VAC control panel? These panels were not labeled with arc flash label before but only shock hazard labeling.

There is not a way to calculate the IEA for single phase below 208?

Thank you.


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 Post subject: Re: 120VAC control panel labeling
PostPosted: Fri Feb 15, 2019 7:08 am 
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Joined: Mon Jan 18, 2010 11:35 am
Posts: 543
Location: Wisconsin
How many of your 120VAC control panels have more than 2kA bolted fault current at them?


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 Post subject: Re: 120VAC control panel labeling
PostPosted: Sun Feb 17, 2019 10:59 am 
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Joined: Tue Oct 26, 2010 9:08 am
Posts: 2174
Location: North Carolina
The exception is not removed. The original exception was a single transformer rated 125 kVA or less with 208 V or less secondary. There are numerous problems with this definition. For instance what if the system is single phase instead of 3 phase? What if there is more than one transformer or say a 3 phase transformer assembled from 3 single phase transformers? What if the supply is a UPS? Or to get more technical what if the impedance (%Z) of the transformer is different? See...all kinds of interpretation problems. The new standard is 2 kA, 240 VAC or less, with a lower 208 VAC cutoff.

So that leaves how to model 120 VAC. You can model this, it's just that IEEE 1584 won't work for you at least using the empirical model. In the annexes there is still the simplified breaker/fuse approach. You can use Lee which is particularly simple, and you can appeal to IEEE C2 (NESC) which has a very simple rule similar to the original IEEE 1584-2002 cutoff, except that it also includes a minimum 4 cal/cm2 PPE requirement. Finally some DC testing (not AC) has been done at 125 VDC and up to 20 kA with a tiny 1/4" arc gap the highest recorded incident energy is right at 1.2 cal/cm2. May want to use DC as an alternative for your model since it will clear most concerns. See also the public inputs for the 2021 NFPA 70E that have references to several DC arc flash papers that definitely apply if you accept that using DC results on an AC system will inherently be conservative (calculates higher incident energy than is possible).


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