Which power rating of the MP-II 5000VA 120vac 24v do I use to size an incoming power breaker for Grid Supply (this system is used for backup power)?
Do I use it’s 5000VA to size this incoming breaker?
OR do i use it’s published max 9000w(peak, short term, but not sure the max time for this rating) for sizing the grid feed breaker?
Thanks!!
Shawn
Size it at least one step lower than your grid fuse from your grid supplier, and look at what the multi can max passthru in data sheet
I would size for 5kVA continuous. 5000 ÷ 120 x 1.25 = 52A. So use a 50A or 60A breaker with appropriately sized wire or cable. The breaker will handle short-term surges depending on its trip curve rating.
No, the unit has 95a transfer capabiliy, so imho he should go for a 125a fuse.
That’s only true if he’s passing through 95A. Shawn said the inverter is used for backing up loads. I assumed the loads will not exceed the capability of the inverter. If he’s passing through power to loads that will not be inverted, then yes, he should size for max pass-thru. But I don’t think that’s what Shawn is intending.
I’d assume being a backup supply, he’s intending to use this as a UPS on the main feeder. If that’s the case the breaker should be sized to the mains breaker or the transfer switch capacity (lower of the 2 of course)
Shawn, time to be more specific about your plans 
I assume you pull some critical loads from the main breaker panel to a critical loads panel connected to the Multi. Dave and Ludo are assuming you want to switch an entire 120V leg coming into the main breaker panel. That doesn’t make much sense, but please let us know your thinking.