Downsizing Main Breaker

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JoeNorm

Senior Member
Location
WA
Hi All,

I have been at this awhile so have downsized a main breaker or two in my day.

The current job I am installing consists of 25 AC modules each rated at 1.33 amps a piece. 25x1.33= 33.25amps 33.25x1.25= 41.56amps

It is hard to downsize a main breaker over 1.56 amps..........is there anything I am missing that might allow this on a 40amp breaker, and therefore not require a downsize of the main?

Main panel is a QO with 200 amp main breaker.

Thanks
 

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
FYI square D does make a QOM2175VH 175-Amp (I see people downsize to a 150).
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
FYI square D does make a QOM2175VH 175-Amp (I see people downsize to a 150).

I did the same thing a year ago with 175 amp breaker but I believe it was a ge breaker. I am pretty sure all manufacturers make them but they are not usually a stock item
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
If it was less than half of one amp over then I think you could make a case for rounding off but I think you're stuck downsizing unless you have a very accommodating AHJ.

I agree about 175A, I never downsize to 150.
 

JoeNorm

Senior Member
Location
WA
Yes, we stock QO 175 on the vans because we do this so often. We're just usually never this "close" to not having to downsize so I was making sure.

I'll go ahead and install the 175. It's hard knowing the array will likely never produce more than 30 amps, let alone 40-50
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Hi All,

I have been at this awhile so have downsized a main breaker or two in my day.

The current job I am installing consists of 25 AC modules each rated at 1.33 amps a piece. 25x1.33= 33.25amps 33.25x1.25= 41.56amps

It is hard to downsize a main breaker over 1.56 amps..........is there anything I am missing that might allow this on a 40amp breaker, and therefore not require a downsize of the main?

Main panel is a QO with 200 amp main breaker.

Thanks

The short answer is no. You can downsize the main breaker or you can upsize the MDP bus.

But we have documentation from Eaton that their Cutler-Hammer panels from 150A to 225A all have the same 225A bus. Maybe you could query SQD and ask them if they do something similar?
 

Carultch

Senior Member
Location
Massachusetts
The short answer is no.

The long answer, is to get your inverters derated by the factory/firmware to have slightly less output current than their standard rating, with a letter for your AHJ to accept. Probably not something that will happen for microinverters/AC modules, and not something practical for a system at this scale.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
The long answer, is to get your inverters derated by the factory/firmware to have slightly less output current than their standard rating, with a letter for your AHJ to accept. Probably not something that will happen for microinverters/AC modules, and not something practical for a system at this scale.

He is using microinverters.
 
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