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 Post subject: 240.67 Maintenance Mode for Fusible Switches
PostPosted: Tue Mar 15, 2022 2:40 pm 
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Joined: Sat Nov 21, 2009 10:23 pm
Posts: 118
Location: Ohio
240.87 (2017 NEC) has indirectly required circuit breakers (=>1200A) to include an energy reduction scheme. The same format/concept has now been required since 2020 for fusible switches. The introduction was a bit skewed, however, if your State has adopted the 2017 or newer version of the NEC, the energy reduction is required for 1200A and greater fusible switches after 1/1/2020.

The key, if the fuse operates faster than 0.07 seconds at the calculated arcing current, the mandated energy reduction scheme is not required. For information purposes, the majority of switches 1200 amps and greater are bolted pressure switches and they usually include a shunt trip mechanism. The lower the ampere rating of the fuse, the more likely the operating time will be under 0.07 sec, therefore, the switch will not require the energy reduction scheme. Once the fuse size is 2000A or greater, the likelihood is high that the switch will need the energy reduction scheme per the NEC.

When I am involved in an arc flash study or NFPA training and I find a equipment fed by a bolted pressure switch where the IE is over 1.2 cal/sq cm, I am recommending the client review the need for the energy reduction relay.

For some reason the site is not allowing me to upload the files
I am trying/attaching the cuts on an arc flash reduction relay kit. I am also attaching a scope trace of the clearing time of a 2000A switch, in other words, the mechanical operating time of the shunt trip/stored energy mechanism of the switch.


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 Post subject: Re: 240.67 Maintenance Mode for Fusible Switches
PostPosted: Mon Apr 11, 2022 12:32 pm 
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Joined: Sat Apr 04, 2009 9:50 pm
Posts: 120
Location: San Antonio, TX
I understand that the requirement to install an energy reduction method for fuses 1,200 A or larger, does not depend on the AFIE of the equipment protected by this fuse. I understand it depends on the opening time of the fuse under arcing current conditions (you do not need to add the bolted pressure switch opening time, just in case).

So, if the arcing current opens the fuse in a time longer than 0.007 secs, you need an energy reducing method. Irrespective of the result of the arc flash study. Also, if the fuse opens in less than 0.007 sec, you do not need an energy reducing method, irrespective of the result of the arc flash study.


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