MPP 6548 selecting the correct AWG

[sabo]

The MPP manual says to use 4 AWG for the AC Input and Output. I assume that is because they assume I will be building a 100 amp system. I have 1 inverter now. I have 6 AWG running from the main panel to my sub panel. I already ran a 6 AWG run off that sub panel for a second sub sub panel. I am now planning on using that 6 AWG run for my inverter and not for the second sub panel as originally planned. If I add an inverter at some point in the future I would run 4 AWG from the main to the sub panel and then again from the sub to the inverters. Are there any problems with this plan?

TIA

 

[BentleyJ]

The MPP manual says to use 4 AWG for the AC Input and Output. I assume that is because they assume I will be building a 100 amp system.

MPP 6548 is supposed to have Over Current Protection of 60A max per unit. 6AWG would be the smallest allowed with 4AWG being a conservative recommendation.

I have 1 inverter now. I have 6 AWG running from the main panel to my sub panel.

Which means the subpanel should be protected by a 60A, 2 pole, or smaller breaker.

I already ran a 6 AWG run off that sub panel for a second sub sub panel. I am now planning on using that 6 AWG run for my inverter and not for the second sub panel as originally planned.

That will work as long as the there is a 60A breaker upstream on the Main Panel that feeds the subpanel that feeds the inverter.

If I add an inverter at some point in the future I would run 4 AWG from the main to the sub panel and then again from the sub to the inverters. Are there any problems with this plan.

4AWG would be a recommended, but not required, upgrade from the Main Panel to the SubPanel and the Breaker could be increased accordingly. It depends on how many other loads are on the subpanel and how they are balanced.
From the subpanel to the inverters, 6AWG would still be acceptable. This line of thought is based on the belief your Subpanel is 240/120V split phase so when you add another inverter the new 60A single pole breaker will be on the other bus bar in the subpanel so both Hot legs are being utilized.

 

[sabo]

MPP 6548 is supposed to have Over Current Protection of 60A max per unit. 6AWG would be the smallest allowed with 4AWG being a conservative recommendation.

Which means the subpanel should be protected by a 60A, 2 pole, or smaller breaker.

That will work as long as the there is a 60A breaker upstream on the Main Panel that feeds the subpanel that feeds the inverter.

4AWG would be a recommended, but not required, upgrade from the Main Panel to the SubPanel and the Breaker could be increased accordingly. It depends on how many other loads are on the subpanel and how they are balanced.
From the subpanel to the inverters, 6AWG would still be acceptable. This line of thought is based on the belief your Subpanel is 240/120V split phase so when you add another inverter the new 60A single pole breaker will be on the other bus bar in the subpanel so both Hot legs are being utilized.

I currently have a 50 amp at the main feeding a 40 amp 240 on the subpanel. Do you think I should have all 60 amp breakers one each for the main the sub and one for the subpanel attached to the inverter?

 

[BentleyJ]

I currently have a 50 amp at the main feeding a 40 amp 240 on the subpanel. Do you think I should have all 60 amp breakers one each for the main the sub and one for the subpanel attached to the inverter?

No, that is not necessary at this point. The 50A breaker in the main panel is fine and the subpanel doesn't need a main breaker at all, they are usually fed by connecting directly to lugs on the bus bars. Not sure what you mean by a 40A subpanel? Is that the size of the main breaker or backfed branch breaker? usually subpanels are referred to by their bus bar rating, 100A or 125A, Etc. regardless the size of the OCPD.
Typically the inverter is connected to the subpanel with its own breaker because its the easiest. Although in this case a breaker would not be necessary, you could technically connect the inverter directly to a feed thru lug on the subpanel bus bar since the whole system starting at the main panel is protected by the 50A breaker. Not all subpanels are going to have feed thru lugs though.

 

[sabo]

No, that is not necessary at this point. The 50A breaker in the main panel is fine and the subpanel doesn't need a main breaker at all, they are usually fed by connecting directly to lugs on the bus bars. Not sure what you mean by a 40A subpanel? Is that the size of the main breaker or backfed branch breaker? usually subpanels are referred to by their bus bar rating, 100A or 125A, Etc. regardless the size of the OCPD.
Typically the inverter is connected to the subpanel with its own breaker because its the easiest. Although in this case a breaker would not be necessary, you could technically connect the inverter directly to a feed thru lug on the subpanel bus bar since the whole system starting at the main panel is protected by the 50A breaker. Not all subpanels are going to have feed thru lugs though.

Yes the subpanel is fed on the bus bars. Its a 125 amp panel. The inverter is fed from a 40amp breaker. Now that you mention it I want to feed my new subpanel next to the inverter by the bus bars due to the fact it only has 8 spaces. I thought I needed to feed the new panel by a 240 V breaker to hit both bus bars. This subpanel is also 125amp. Fortunately it has lugs.

 

[BentleyJ]

You can energize both bus bars with the same 120V Hot from the inverter. Of course its still just a 120V panel. You will need a way to properly split the single Hot from the inverter into 2 wires, one for each subpanel bus bar lug.

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