Breaker on line side of ATS

[electrofelon]

So I know this has come up before: The question of if I can put, say, a 400A OCPD ahead of a 200A transfer switch. It seems article 404 would cover an ATS and there is no requirement to protect a switch at its rating with an OCPD. However, I have also agreed with most that theres a 99% chance the manufacturer instructions will require protection at the ATS rating. I guess I kinda assumed this without ever actually seeing it. So I am looking at a kohler RXT transfer switch. Unless I missed it, I didnt see anything in the manual requiring OCPD protection at its rating. Also look at the attachment which is the SCCR ratings. They seem to be allowing an 800A OCPd on a 400A switch. Any comments?

 

[augie47]

One approach ! Full size or reduced size conductor to the ATS ?
If it's not full size then the 240,21 tap rules require termination in an overcurrent device.

 

[electrofelon]

One approach ! Full size or reduced size conductor to the ATS ?
If it's not full size then the 240,21 tap rules require termination in an overcurrent device.

Thats a good point, I didnt think of that angle: probably cant terminate 400A of conductor on a 200A switch, so theres going to be a point only so high you can go. Maybe with some pin reducers and CU conductor you can get somewhat over......

 

[dkidd]

Take a look at https://forums.mikeholt.com/threads/400a-ats-and-600a-bkr.2563594

 

[electrofelon]

Take a look at https://forums.mikeholt.com/threads/400a-ats-and-600a-bkr.2563594

I see the switch you referenced in that thread is a Cummins. What model is it? I just looked at a Cummins manual and could not find such a statement. In fact it had a chart saying the OCPD can be bigger than the ats rating.

Edit:. Ok I see, your says protected by OCPD but not "at its rating". The OCPD can be larger.