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 Post subject: UL 891 Switchboard, Main PD Isolation, and RELT
PostPosted: Mon Dec 19, 2022 3:18 pm 

Joined: Tue Oct 12, 2021 10:20 am
Posts: 9
All, it appears that some discussion indicate that UL 891 Switchboards probably will not provide enough ready barriers to stop an arc flash from propagating to the main section and disabling the Main PD. Yet with the NEC requirement that 1200A and larger main breakers have RELT and the labeled PPE be able to rely on it, if a manufacturer/UL shop provides a RELT on their main breaker are they indicating their switchboard will provide downstream section flash isolation? Thus UL891 Switchboards that are now required to have RELT do have adequate isolation from downstream sections to the main section?


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 Post subject: Re: UL 891 Switchboard, Main PD Isolation, and RELT
PostPosted: Tue Dec 20, 2022 7:42 am 
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Joined: Thu Apr 18, 2019 11:42 am
Posts: 110
Unless there is a barrier between the main and feeder sections...my opinion is the arc reduction switch is worthless. Our design engineering group installed some new equipment with them and in many cases there is no barrier or isolation. Would love to hear others comments.

Mike


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 Post subject: Re: UL 891 Switchboard, Main PD Isolation, and RELT
PostPosted: Thu Dec 22, 2022 7:00 am 
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Joined: Wed May 07, 2008 5:00 pm
Posts: 879
Location: Rutland, VT
I agree with Mike. Unless there is substantial barrier between the main breaker with a RELT or the main breaker is mounted in a separate enclosure, there are no benefits to the RELT.

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 Post subject: Re: UL 891 Switchboard, Main PD Isolation, and RELT
PostPosted: Mon Jan 09, 2023 12:52 pm 

Joined: Fri Sep 28, 2018 7:32 am
Posts: 37
Location: Sioux Falls, SD
This has bothered me for several years now. I've tried to get an informational note added to NFPA 70 to inform users that some arc reduction technology like RELT may provide a false sense of safety. Without adequate barriers, if a main with RELT is in the same enclosure as other breakers then it's benefits cannot be realized at that panel. If, activating RELT creates miscoordination then there may be benefits but only to the downstream equipment. Better guidance should be given. Better engineering should be applied. These devices should be used properly along with written safe work practices.

Unfortunately manufactures and others seemingly mandate the addition of RELT with little thought given to the application.


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 Post subject: Re: UL 891 Switchboard, Main PD Isolation, and RELT
PostPosted: Fri Jan 27, 2023 10:08 am 
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Joined: Mon Jan 18, 2010 11:35 am
Posts: 570
Location: Wisconsin
jmoore284@gmail.com wrote:
Unfortunately manufactures and others seemingly mandate the addition of RELT with little thought given to the application.


This is a training issue.
While the RELT is unlikely to help at the point where it is installed it can be used to mitigate issue with downstream equipment.

Arc Flash training needs to emphasize devices cannot 'protect' themselves. They only protect downstream locations.


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 Post subject: Re: UL 891 Switchboard, Main PD Isolation, and RELT
PostPosted: Thu Jul 27, 2023 3:49 am 

Joined: Thu Jul 27, 2023 3:46 am
Posts: 1
having a RELT on the main fuse of the Switchboard UL 891 does not automatically guarantee sufficient safe isolation between the infrastructure parts in the Switchboard


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 Post subject: Re: UL 891 Switchboard, Main PD Isolation, and RELT
PostPosted: Thu Sep 21, 2023 10:30 am 

Joined: Tue May 29, 2018 8:19 am
Posts: 44
So this leads to the question: what constitutes a substantial barrier?

I have seen switchboards and switchgear with full section metal barriers, but with openings for the horizontal bus. Sometimes insulating material such as GPO-3 fiberglass board is used to cover the gap around the bus bars. Sometimes GPO-3 is used as the entire barrier material. Are any of these substantial enough to stop the propagation of an arc?

In a medium-voltage (4.8kV) application a while back an arc propagated between sections that appeared to be well barriered. In this case epoxy bushings were used where the bus penetrates section barriers. There were scorch marks around the joints between the barriers and the enclosure walls which made me think enough hot gas or dust moved through those joints to ignite an arc in the adjoining sections in what appeared to be a chain reaction that resulted in evidence of arcing in several sections. I don't know if this is common, and maybe it can only happen at higher voltage.

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