AC breaker requirements, max output vs max apparent power from utility?

[Jankzilla]

Hi guys,

I have a question about AC breaker size. My impression was that the breaker needs to be spec'd for the max sustained output of the inverter. So in my case I have a Goodwe GW3048-EM which has a max ouput (while grid supplied) of 3kW. So if I add 25% I get 3.75kW, divided by 230V is 16.3A. Supposedly you can round down if you are less than half an amp over the nearest standard size. So presumably 16A breakers would be fine.

However I am a bit perplexed by something on the data sheet. It says "Max. Apparent Power from Utility Grid - 5300VA". Now I know there is a bunch of stuff related to power factor and the types of loads you run (though you shouldn't be running heavy inductive loads on this inverter at all) resulting in a difference in your real power vs apparent power. But I just don't know where that number comes from. My thought was that it could be a momentary number for a few milliseconds, or perhaps if you are passing 3kW through from the grid and charging the batteries at 2.4kW? My assumption is that is not possible with this inverter, though I could be wrong.
At any rate, if anyone could help explain this or point me in the right direction I would appreciate it. I'm pretty sure 16A would work but I'm trying to make sure I understand what I am doing, not just making something that should probably work.

JZ

 

[RCinFLA]

Depending on inverter and how you use it, breaker amperage is usually based on hybrid inverter maximum pass-through relay amperage.

Actual inverter has its own detection for overload shutdown.

 

[Jankzilla]

Depending on inverter and how you use it, breaker amperage is usually based on hybrid inverter maximum pass-through relay amperage.

Actual inverter has its own detection for overload shutdown.

Thanks RC,

So in this case that would be 3kW correct? I wonder where this 5300VA number comes from.

JZ

 

[RCinFLA]

Breakers care about amperage, not real or apparent power.

 

[Jankzilla]

Right. I overlooked the part where it says 23.6A from grid. That's like 5.4kW at 230V. That seems like a lot for a 3kW inverter.

 

[zanydroid]

Power factor is relevant for breakers if you have significant load because simple attempt to convert from real power to current will not yield accurate result. For most residential loads though, you don’t really need to pay attention to it since most major home appliances have power factor correction.

If you are running motor loads with no PFC or a lot of small switching power supplies without PFC then maybe the apparent power vs real power difference will become meaningful.

 

[time2roll]

Thanks RC,

So in this case that would be 3kW correct? I wonder where this 5300VA number comes from.

JZ

Inverter needs to produce the full 5300VA. Probably should have 6k+ inverter.

Because the load does not pull from the full sine wave more apparent power needs to be available.

Here is a little explanation for a pf corrected charger vs not pf corrected. Same thought applies to any load.
https://xantrex.com/library/inverters/prosine-inverter/power-factor-correction/

OK possibly if the additional apparent power is only needed at start up you could rely on the inverter surge performance to supply the increased apparent power for a few seconds.

 

[Hedges]

32A breaker according to manual.

I think those three models on the data sheet can take different amounts of power from PV and backfeed grid with it,
but all three can pass 5300 VA from grid to your loads. So you should size breakers according to that figure.
For some reason, with grid down and supplying backup power, all three are limited to 2300 VA output.
That seems to come from the 50A (at 48V nominal) battery current limitation.

You would expect PV to support loads while the sun shines, add to available power.
I have a suspicion it is not capable of charging battery from PV while grid is down. Just functions as a battery UPS, and a separate GT PV inverter, but those two functions don't work together as a stand-alone unit. However, manual (slide 3) says "If the grid fails, the system automatically switches to back-up mode, in which the load can be supplied by the PV or battery"

https://en.goodwe.com/Ftp/EN/Downloads/User%20Manual/GW_EM_User%20Manual-EN.pdf

Slide 8 says to use 32A breaker

"AC breaker specification 32A / 230V (e.g. DZ47-60 C32)"

"Accepted Loads:

The EM series inverter is able to supply a continuous 2300VA output or max 3500VA in less than 10 seconds on the back-up side to support back-up loads. The inverter will derate for self-protection at high ambient temperatures.

• Acceptable back-up loads: Television, computer, fridge, fan, illumination lamps, microwave oven, electrical rice cooker and router etc.

• Unacceptable back-up loads: Air conditioner, water pump, heaters, washing machine, electromagnetic oven, compression engine, hair drier and vacuum cleaner etc. Any other loads with high inrush current at start-up are also unacceptable."