Inverter output breaker sizing

[hhsting]

I have 9kW inverter at 208V three phase. Full load amps is 24.9A. When I take 24.9x1.25=31.22A. Next standard rating would be 35A breaker however plans shows 40A. Would 40A be acceptable or not?

 

[rickb101260]

As a Plan Reviewer, if it says 35A, that's what it needs to be, "Next Size Up" based on Inverter Maximum Continuous Output Current rating. 2014 NEC 240.4(B). With that said though, the 'Rona has put a hurting on suppliers and for some reason, 35A are impossible to find or at least here in Central Florida they are. As an inspector, I'm okay with a 40A IN THIS CASE.

 

[jaggedben]

40A is fine if it protects the wire according to 240. 705 puts a minimum size on the wire and overcurrent protection. The only reason you'd have to use a 35A breaker instead of sizing everything to 40A or higher would be if the manufacturer had a maximum OCPD size on the label or instructions.

 

[hhsting]

40A is fine if it protects the wire according to 240. 705 puts a minimum size on the wire and overcurrent protection. The only reason you'd have to use a 35A breaker instead of sizing everything to 40A or higher would be if the manufacturer had a maximum OCPD size on the label or instructions.

Inverter is Solaredge and so manufacturer instruction says 125% and next higher standard rating I think for sizing

 

[jaggedben]

Inverter is Solaredge and so manufacturer instruction says 125% and next higher standard rating I think for sizing

I don't recall that for single phase inverters but if you've got the docs then so be it.

 

[hhsting]

I don't recall that for single phase inverters but if you've got the docs then so be it.

I don’t and inverter is three phase

 

[Carultch]

Inverter is Solaredge and so manufacturer instruction says 125% and next higher standard rating I think for sizing

Unless it specifies maximum, that could be a guideline as opposed to a limit.

On PDF page 13 (printed page number 12) of this document, it indicates the following, which answers our question. I don't know why they don't specify this in the same context as where we found 125% calculation spelled out, as that would make it a lot easier to find.

https://www.solaredge.com/sites/default/files/se-single-and-three-phase-inverter-user-manual-na.pdf

Three phase 9, 10, 20 kW inverter must be connected to a dedicated AC branch circuit with a maximum Overcurrent Protection Device (OCPD) of 40A. Three phase 14.4, 33.3 kW inverters must be connected only to a dedicated AC branch circuit with a maximum Overcurrent Protection Device (OCPD) of 60A.

The reason the 10kW and 20kW inverters are grouped with the 9kW inverter, is that they are the 480V counterparts to the 9kW inverter for the 208V grid. Likewise, 33.3 kW is the 480V counterpart to 14.4kW inverter at 208V.

The related inverters whose essential difference is grid voltage have similar output current ratings, similar internal components whose selection is governed by ampacity, and similar criteria for the output circuit construction. You can expect power rating to be scaled, as a result of the same amps at a different voltage. You will also notice that the 208V SolarEdge inverters to run at 600V and less on the DC-side, while their 480V counterparts have 1000V strings.