Growatt 24v Vagueness with breakers

[griftin]

I apologize if this has been discussed but I could not find a specific answer to this question. I have a growatt 3000 watt 24v all in one system. I'm powering it using two 12v 200 amp hour lithium ion batteries set up in series. I am running a 200 amp breaker between the battery and the inverter. I am now working on the AC output, not the input. I am planning on powering a small cabin and just want to run some lights and other small electronics. Based on the 3,000 watts and 120 volts, my understanding is the max breaker I want to use is 30 amps. I planned on putting a 30 amp two-post breaker into a standard breaker box, and then feeding the 120 directly into the breaker and jumping it to the other side of the breaker and using that as the main switch. I would then add single pole 20 amp breakers that would feed out to the lights and outlets. However, I was watching a video and saw some discussions in here where someone was using a 60 amp for the master, and someone mentioned using a 40 amp as well. Now I know the 40 amp is also the suggested size for the AC input. My question is what are the right sizes?

If you need to know any other details, please let me know as I'm relatively new on this website so I don't know what kind of details are expected. Thanks

 

[rmaddy]

3000W / 12V = 25A. A 30A breaker is 20% more than 25A. The only reason I can see using anything bigger than 30A for the main breaker is if your inverter supports more than 3000W for 30 seconds (or similar) and you wish to be able to take advantage of that higher power.

Also keep in mind that even if you are adding multiple 20A branch breakers, the 30A main will help protect things if you plug in too many loads. For example, let's say you plug in three different 15A loads into 3 different outlets on three different branch circuits. No one load will trip its own 20A breaker but the combined load of 45A will trip the 30A main breaker because it's too much. And the inverter won't like trying to push out 30A anyway. So using something like 40A or 60A as your main breaker would be a problem because it would allow those three loads to try to pull too much from the inverter. This might actually be an argument to use a 25A main breaker since that's the most the inverter can provide (other than possible short term surge loads).

 

[John Frum]

30 amps requires 10 awg minimum, hopefully that is compatible with the minimum size for the main lugs of your panel.
The master breaker is intended to protect the wire.
If you move up in wire size you can(optionally) move up in breaker ampacity.

 

[griftin]

30 amps requires 10 awg minimum, hopefully that is compatible with the minimum size for the main lugs of your panel.
The master breaker is intended to protect the wire.
If you move up in wire size you can(optionally) move up in breaker ampacity.

I'm planning on using 8 gauge as that's the suggested gauge in the manual. That should keep me protected for the 30 amps.

 

[griftin]

3000W / 12V = 25A. A 30A breaker is 20% more than 25A. The only reason I can see using anything bigger than 30A for the main breaker is if your inverter supports more than 3000W for 30 seconds (or similar) and you wish to be able to take advantage of that higher power.

Also keep in mind that even if you are adding multiple 20A branch breakers, the 30A main will help protect things if you plug in too many loads. For example, let's say you plug in three different 15A loads into 3 different outlets on three different branch circuits. No one load will trip its own 20A breaker but the combined load of 45A will trip the 30A main breaker because it's too much. And the inverter won't like trying to push out 30A anyway. So using something like 40A or 60A as your main breaker would be a problem because it would allow those three loads to try to pull too much from the inverter. This might actually be an argument to use a 25A main breaker since that's the most the inverter can provide (other than possible short term surge loads).

I'm in the same mindset. Even though I'm only going up 10 amps, I think the 30 amp in front is a good safety measure. I just I'm so confused by someone would use a 60 amp on a 3000w 120v inverter. Thought maybe there was something I just didn't know

 

[rmaddy]

I'm so confused by someone would use a 60 amp on a 3000w 120v inverter.

Many 3000W inverters support a brief 6000W surge. If that's something someone would want to make use of then a 60A breaker makes sense. Of course that requires proper wiring and everything else to make that safe.

 

[740GLE]

What breaker service panel are you using? Typical spout phase 100/150a panel?

Sounds like you will just be back feeding a dual pole “240v” bkr but with just 120v going to both legs of the service panel?

 

[740GLE]

Many 3000W inverters support a brief 6000W surge. If that's something someone would want to make use of then a 60A breaker makes sense. Of course that requires proper wiring and everything else to make that safe.

I’d wager the surge is quicker than the operating of a 30a bkr.

 

[griftin]

What breaker service panel are you using? Typical spout phase 100/150a panel?

Sounds like you will just be back feeding a dual pole “240v” bkr but with just 120v going to both legs of the service panel?

Just a standard 6 slot. I'm putting a 2 pole 30 amp breaker and feeding the live directly through that. The rest will be 1 pole 20 amps. Once I get it built, I plan on posting it on show and tell for a final opinion

 

[Cornwallav8r]

30 amps requires 10 awg minimum, hopefully that is compatible with the minimum size for the main lugs of your panel.
The master breaker is intended to protect the wire.
If you move up in wire size you can(optionally) move up in breaker ampacity.

Right. Choose conductor that carries full load from 75c column. Then protect upstream with 125% larger breaker over conductor ampacity.

 

[Cornwallav8r]

Many 3000W inverters support a brief 6000W surge. If that's something someone would want to make use of then a 60A breaker makes sense. Of course that requires proper wiring and everything else to make that safe.

Understand what a circuit breaker is. It's a time inverse device, meaning the higher the current the shorter the time to trip. All good breakers come with an actual trip curve showing amps versus time, it comes in handy in coordination studies. Rarely used except complex industrial installations, to prevent say a 20a single pole breaker for example, from tripping the whole building 2000a main. Point is, it's just a bimetal switch and works on a time to heat principle.