It is currently Fri Sep 18, 2020 11:01 am



Post new topic Reply to topic
Author Message
ekstra   ara
 Post subject: Annex R Working with Capacitors in NFPA 70E 2021 Thoughts?
PostPosted: Mon Aug 24, 2020 8:02 pm 

Joined: Tue Aug 18, 2020 3:14 pm
Posts: 3
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?


You do not have the required permissions to view the files attached to this post.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Annex R Working with Capacitors in NFPA 70E 2021 Thought
PostPosted: Mon Aug 31, 2020 8:30 am 

Joined: Mon Dec 17, 2018 8:17 pm
Posts: 1
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.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Annex R Working with Capacitors in NFPA 70E 2021 Thought
PostPosted: Fri Sep 04, 2020 9:12 am 

Joined: Tue Aug 18, 2020 3:14 pm
Posts: 3
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.


Top
 Profile Send private message  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 3 posts ] 

All times are UTC - 7 hours


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
© 2019 Arcflash Forum / Brainfiller, Inc. | P.O. Box 12024 | Scottsdale, AZ 85267 USA | 800-874-8883