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Annex R Working with Capacitors in NFPA 70E 2021 Thoughts?
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Author:  wfg42438 [ Mon Aug 24, 2020 8:02 pm ]
Post subject:  Annex R Working with Capacitors in NFPA 70E 2021 Thoughts?
Hello Everyone,

As many of you may know in the 2021 edition there will be a new informative annex R which deals with Capacitor Banks.

This annex provides equations for the estimation of the stored energy in Capacitor banks which can be used to generate labels for these pieces of equipment.

The equations seem straightforward however one thing that is puzzling is the determination of the discharge time from nameplate data.

When sampling various capacitor banks I noticed that most banks advertise a specific discharge time however typically the discharge R is not mentioned. .

For example take this sample capacitor bank :
https://www.ebay.com/itm/GE-Power-Facto ... SwJ-9exYlN


If the discharge time is not legible on the nameplate what approach can be taken to find the discharge R?

Has anyone had experience with this or see a practical approach to determining the discharge resistance?

Attachments:
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Author:  rzieg1224 [ Mon Aug 31, 2020 8:30 am ]
Post subject:  Re: Annex R Working with Capacitors in NFPA 70E 2021 Thought
According to Article 460 in the National Electrical Code, the capacitor is supposed to discharge to a voltage less than 50 nominal within 60 seconds after the capacitor has been disconnected from the source. NEC 460.6(A). 460.6(B) says the discharge method cannot be manual.
Author:  wfg42438 [ Fri Sep 04, 2020 9:12 am ]
Post subject:  Re: Annex R Working with Capacitors in NFPA 70E 2021 Thought
That's correct, I saw NECs requirements for the discharge time and that it should be built in.

The methodology listed in Annex R of the latest NFPA 70E 2021 draft gave me the impression its expected for users to determine the permanently mounted discharge resistance in order to list the discharge time of the bank when disconnected from the source.

If a facility wants to generate Warning labels for capacitor banks is it safe to say most would not follow the equations in annex R?

Would one simply print on the labels the banks indicated discharge time (if its readily available that is) ?

It seems it may be unrealistic attempting to calculate the potential discharge time using the equations in Annex R since the oem mounted discharge resistor values are not readily available from what I have seen in sample equipment.
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