What am I missing? Current to house is on worst day of summer is only 37.5A?

[scottvanv]

Hey y'all, I live in Texas, which means that in August, we're drawing a lot of power around 3 PM to power the AC. According to my electric bill, between 3 - 4 PM on the worst day last year, I used 9.96 kWH of electricity. Divide by one hour, and that gives me an average wattage during that hour of 9.96kW. Divide that by 240 volts = 41.5 Amps of current. Even accounting for surge, at double that, say 80A, that's just over only half of what my panel, 3/0 underground wire, and breaker at my meter are rated for, 150A. My home was built in 1980 ... and by the looks of it none of grid-to-house circuitry has been touched since. I'm putting in an off-grid/hybrid system (NOT feeding the grid, but connected to it for backup), my inverters cannot be near my main panel, and I'll be bypassing from the main 3/0 grid input line to an on-off-on switch to the inverters, then back to the main panel (so that I can avoid rewiring my entire house). I'm trying to size the wire run from the switch to my inverters, and that 41.5 Amps seem awful low to me. Just looking for a sanity check on my math ... thanks in advance!!

 

[Ampster]

Your math looks correct. 6AWG is rated for 60 Amps. Is the 3/0 cable from a battery? What voltage is the battery?

 

[scottvanv]

Your math looks correct. 6AWG is rated for 60 Amps. Is the 3/0 cable from a battery? What voltage is the battery?

The 3/0 is what's coming from the grid, underground to my breaker box on my house from my meter at the back of my yard. I've got two MPP Solar 6548s ... specs say they can each take a max of 60A / 150V, and their parallel wiring diagram shows L1 and L2 going into each, below. When I'm looking up the correct wire size, looks like I use 60A, and according to this calculator, that's 4 AWG. Does that mean that my entire house will now be limited to 60A?

 

[400bird]

Does that mean that my entire house will now be limited to 60A?

With the description I read, yes if the max pass through is 60 amps, then the maximum you can pass through the inverter is 60 amps.

The MPP spec sheet is sparse on details. But, it looks like a max output of 54 amps (6.5kw) no continuous rating. Also, it's a high frequency inverter, as such, it probably can't start your AC.

You need to size the wire run for the max load, not expected average load. Plus, if you're running a long distance, you need to consider voltage drop.

 

[scottvanv]

Heh, yep, "sparse on details" is quite the understatement. Per below, it says it handles "2*rated power for 5 seconds" so I'd think the 6500W number is the continuous number. From other dealings with this spec/company, this is an intelligently made box, but man do they have comms problems, as evidenced by total lack of clarity in their specs AND in direct emails with them.

Yesterday I went and put a clamp meter around L1 and L2 in my panel when both my AC and hybrid water heater heat pumps were on (by far the main draws of my house) along with other normal family activity = 32 and 35 Amps respectively. I'm likely good on the 60A per leg, given that I have a soft starter waiting to be put on my central AC, along with the 2* surge rating. I also have 5 hyper efficient mini-splits waiting to be installed (that I'll be running in parallel with the central AC, minimizing its relative inneficiency), each at min 10A (15A CB), with the odds that ALL of them surge at exactly the same time almost next to impossible. I guess what was tripping me out about my original math was WHY were "they" running 150A to a house, and my neighbor (who's meter/main switch is on my property) with the same size house, has been modernized/upgraded to 200A? Given that I'm a family of four with likely more than prototypical usage, what are folks doing that requires 200A nowadays?! (I kind of "get" the 150A 30 years ago ... as they would have been less efficient and also allowing headroom for growth.)

Where do you get the 54A number? 91% efficiency * 60A?

 

[scottvanv]

With the description I read, yes if the max pass through is 60 amps, then the maximum you can pass through the inverter is 60 amps.

The MPP spec sheet is sparse on details. But, it looks like a max output of 54 amps (6.5kw) no continuous rating. Also, it's a high frequency inverter, as such, it probably can't start your AC.

You need to size the wire run for the max load, not expected average load. Plus, if you're running a long distance, you need to consider voltage drop.

Oh, and the voltage drop ... it's only 30 ft, so it looks like around a 1% drop at 4 awg ...

 

[400bird]

54 amps is the rated output current.

6500 watts/120 volts = 54.17 amps.

That spec sheet you've got has even more info than I found.

I'm confused as how they can do 205% for 100ms but also 2x rated current for 5 seconds.
Unless somehow the difference difference in load between 205% and 200% allows the inverter to output for an additional 4.9 seconds.
Spec sheets like that give me lots of doubt.

 

[scottvanv]

54 amps is the rated output current.

6500 watts/120 volts = 54.17 amps.

That spec sheet you've got has even more info than I found.

I'm confused as how they can do 205% for 100ms but also 2x rated current for 5 seconds.
Unless somehow the difference difference in load between 205% and 200% allows the inverter to output for an additional 4.9 seconds.
Spec sheets like that give me lots of doubt.

Yep, like I said, I went through A LOT to understand another spec, an 18A PV input max, which would be quite a stupid number, as most panels today are ~10A, making it impossible to run anything in parallel. Turns out, that max input number is 25A, with the 18A being what it clips at. So, box design smart, piss poor comms. I'm in tech, been dealing with these smart design / comms problems my whole career. I'll presume the same on the surge / protection numbers, especially given that I shouldn't be getting too close to the them anyway ...