Inverter cable / circuit breaker

[Greenie]

Hi,
Me again.
I have a 5.6 kW Solar PV system with 7.5kWh batteries and 5kW inverter. My problem is that I think the MCB on my solar circuit is too small.
Originally, my inverter was gagged back to act as a 3.7kW inverter, until I got DNO approval to export more than 16amps, which I now have.
My installer says that they have 'turned up the inverter' to its full potential. So, this weekend, I ran 5kW of kettles on the system to see how it would cope with the load. At the inverter display, the power rating never went above 4kW. I scrolled through the menus and found that the on-grid power is set to 75%. I reckon it should be set to 100%. What does anyone think?
On another point, the MCB protecting the system is rated at 20amps, which seems ok for a 3.7kW inverter but undersized for 5kW. As per page 9 of the instruction manual. My guess is that it should be 32amps.
On another point, the cable is 4mm t&e, which I think looks about right for a 15m run in trunking. Any help would be great.
Cheers

[gumpster1981]

Technically your right, if your putting 5KW t the grid you’d be pushing near 21A through the MCB so technically they should have installed a 25A or 32A, 4mm is fine at those ratings however I would prefer to see a 6mm installed, I suppose practically though it all depends on how often you will be pulling 5KW and for how long, as for short periods you will be fine as you are and yes, you’d want the pier output to be set to 100%

Qualified electrician, 18th edition, 25 years experience

[Lloyd09]

It's great to be a member of the forum, and I also have a question on cable sizing that links into this topic.

I have just bought an all in one 3.7kw system with 10kW of batteries. Looking at the manual, it seems to recommend 10mm cable between the system and the consumer unit and 50amp circuit protection.

This seems way over the top. Am I missing something, and in addition, what type of cable would be advised as I was thinking flex based on the connector provided.

Thanks in advance.

[gumpster1981]

It's great to be a member of the forum, and I also have a question on cable sizing that links into this topic.

I have just bought an all in one 3.7kw system with 10kW of batteries. Looking at the manual, it seems to recommend 10mm cable between the system and the consumer unit and 50amp circuit protection.

This seems way over the top. Am I missing something, and in addition, what type of cable would be advised as I was thinking flex based on the connector provided.

Thanks in advance.




If you have a 3.7 inverter then the most it can provide to the house or draw from the grid is 3.68KW or 16A. 3680W/230V =16A

So based on that a 10mm cable is massive overkill unless your inverter is a very long way from your consumer unit, I would install a 4mm or 6mm if you want to future proof, on a 20A MCB/RCBO. Type of cable will depend on installation but generally for a domestic install you could use twin amd earth or SWA cable to a local isolator next to you inverter then you can flex from the isolator to inverter with round flex cable to terminate into the plug provided

[Lloyd09]

Thanks all for the great feedback.

Do you really need the isolator on the AIO all in one as it does have isolation built in unless you want to switch from flex to armoured?

[gumpster1981]

personally I like to see an external isolator, from a safety perspective if someone needs to work on the AIO itself then it can be isolated at the external local isolator, but for asthetics then if it has a built in isolator you may prefer that, both ways are fine.