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| Maintenance mode setting philsophy https://brainfiller.com/arcflashforum/viewtopic.php?f=4&t=5729 |
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| Author: | alehman@gbateam.com [ Wed Sep 13, 2023 2:52 pm ] |
| Post subject: | Maintenance mode setting philsophy |
My approach to settings for the energy-reducing maintenance mode for circuit breakers has been to use the minimum available pickup and delay settings, except for long-time pickup, regardless of impact on system overcurrent coordination. While the text of NEC 240.87(3) does not stipulate this, I think the intent is clarified in Informational Note No.1: Quote: "An energy-reducing maintenance switch allows a worker to set a circuit breaker trip unit to “no intentional delay” to reduce the clearing time while the worker is working within an arc-flash boundary..." and the NEC Handbook text: Quote: "An energy-reducing maintenance switch is a means by which an intentional delay in the opening of a circuit breaker can be overridden while maintenance, service, or diagnostic tasks are being performed." Recently I have encountered individuals who take the approach that the maintenance mode should accomplish a reduction in potential arc-energy, but not necessarily eliminate all time delays. One engineer recently told me that the goal in maintenance mode should be to reduce arc-energy to the extent possible while maintaining coordination. I feel like this does not meet the intent of the NEC. Others have argued, perhaps justifiably, that the goal in maintenance mode should be to trip with no intentional delay at the calculated arcing fault current. This is the requirement for 240.87(5), but not in 240.87(3). I feel that using anything other than minimum available pickup and delay settings in maintenance mode (other than long-time pickup) does not meet the intent of the rule. Other thoughts? |
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| Author: | mpparent [ Thu Sep 14, 2023 2:35 pm ] |
| Post subject: | Re: Maintenance mode setting philsophy |
If I'm not mistaken, manufacturer defaults are to have the LT the same as normal mode, and all of the other settings to their lowest. They can be changed, but I think if you want to maximize worker safety, you would institute a minimum settings profile. Also, keep in mind since most of the settings are at minimum...better not start large motors in that case. Mike |
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| Author: | alehman@gbateam.com [ Fri Sep 15, 2023 7:17 am ] |
| Post subject: | Re: Maintenance mode setting philsophy |
mpparent wrote: If I'm not mistaken, manufacturer defaults are to have the LT the same as normal mode, and all of the other settings to their lowest. They can be changed, but I think if you want to maximize worker safety, you would institute a minimum settings profile. Also, keep in mind since most of the settings are at minimum...better not start large motors in that case. Mike Yes, I believe that is correct and that starting large motors could be problematic in maintenance mode. |
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