Maintenance Mode Switch

[Curt Fitz]

We were told that the NEC requires an MMS on all distribution panels. I cannot find the provision, even with the NFPA Link. Help?

 

[hillbilly1]

I don’t know about all DP panels, but I have seen them on new ground fault mains.

 

[tom baker]

A distribution panel is not defined in the NEC. But I suspect the MMS is related to arc energy reduction, it’s not an area I am familiar with. I would start by looking in Art 100 definitions and 240 Overcurrent Protection.

 

[hillbilly1]

A distribution panel is not defined in the NEC. But I suspect the MMS is related to arc energy reduction, it’s not an area I am familiar with. I would start by looking in Art 100 definitions and 240 Overcurrent Protection.

Correct, may not be an NEC thing, but an OSHA

 

[petersonra]

240.67 (B)(2). It is one option if using fuses rated 1200 A or higher with a clearing time of more than 0.07 seconds.

0.07 seconds is about 4 cycles.

effective date jan 1, 2020.

 

[hillbilly1]

It is used to reduce the arc flash energy while the equipment is being serviced. Probably to a level that PPE can be used.

 

[David Castor]

I'm aware of NEC 240.67 (Fuses) and 240.87 (Breakers) regarding arc-energy reduction. These requirements are for devices 1200 A or higher.

 

[don_resqcapt19]

I'm aware of NEC 240.67 (Fuses) and 240.87 (Breakers) regarding arc-energy reduction. These requirements are for devices 1200 A or higher.

And they are the only requirements in the NEC.

 

[tom baker]

We were told that the NEC requires an MMS on all distribution panels. I cannot find the provision, even with the NFPA Link. Help?

Good question, thanks for asking. When someone tells you that MMS are required on all distribution panels, or similar, ask fora reference. Or ask here, that way we can all learn…