Solar PV "Power failure"? Technicians in North East? Help!

debitcardmayhem

Just ring one of the solar people that have been found for you . 

paul991

Are you actually trying to cure a problem or just on here to get attention?

Qyburn

paul991 said:

The mcb protects the cable and circuit supplying the inverter. So should only be changed by a electrician who can take into account other things like installation method ect

While agreeing that cable size etc needs to be checked to confirm disconnection times can be met, I'll just point out that at least one vendor (Solaredge) specifies that the protective device should be 20% over the rated current of the inverter. Obviously cable needs to match as well.

Qyburn

Telegraph_Sam said:

That being so it's unfortunate that, playing "safe" I have purchased a replacement 16 A MCB together with an RCD both to the original spec. 

I believe that breakers for solar inverters are now require to switch both L and N. That’s what I was told when ours was being replaced. Ours is an RCBO, so I'm not 100% sure the same applies to an MCB, but I don't see why it wouldn't.

Just while talking about this, a note about your RCD. We haven't seen a schematic but normally where you have separate RCD combined with MCBs for the final circuits, normally the RCD protects multiple circuits. So if it trips randomly that could be triggered by something elsewhere in the house

Netexporter

I checked my G98 inverter and was surprised to see the breaker was rated at 25A. The consumer unit was fitted as part of the install.

NedS

Qyburn said:

paul991 said:

The mcb protects the cable and circuit supplying the inverter. So should only be changed by a electrician who can take into account other things like installation method ect

While agreeing that cable size etc needs to be checked to confirm disconnection times can be met, I'll just point out that at least one vendor (Solaredge) specifies that the protective device should be 20% over the rated current of the inverter. Obviously cable needs to match as well.

That was my point. My 3.0kW FoxESS inverter has a 20A MCB, and Tesla specify a 20A MCB for their latest PW3 when limited to 3.68kW, so it's not at all uncommon to specify a 20A MCB on a 3.6kW inverter.

Netexporter

Probably as well the breaker on mine is a bit bigger as they seem to have forgotten to set the inverter at 3.68kW, so I get the full 4048W maximum continuous rating, on the rare occasions the sun shines properly.

Telegraph_Sam

Heedtheadvice said:

No no NO!

Do not replace the 16A  breaker ( MCB) with  20Amp version.

The 16 A breaker is rated to protect the wiring  ( and hence the subsequent equipment, but by design the wiring ). A 16A breaker ( as I wrote previously) reacts to the level of current passing through it and the duration of the overload. Typically it will break the circuit at twice the rating after a couple of seconds overload I.e. 32A for  16 A breaker and thus protecting the wiring from over heating 

 20 Amp breaker reacts similarly but at 40A.

The inverter, under normal  generation circumstances will limit it's output to comply with the G98 spec of 16 A nominal.  Even under limit failure case it's output will not significantly increase more than the solar PV max output ( kWp ) so there is no need to increase the mcb rating and it could be positively dangerous to do so if the inverter were to fail and draw high current from the grid.

At the moment your mcb is either doing it job ....or is itself in need of replacement specifically with the correct ratings.

I think that the best route would be to get an electrician to replace the existing 16 A MCB with the identical new one in case there is a fault with the former - and/or any external fault responsible for the erratic behaviour. Ditto RCD.

Telegraph_Sam

I think the task will be to establish if there is an "external fault" and/or a fault with one of the original breakers. Does the same [16 / 20 Amp] limit apply to both the RCD and the MCB, or can they differ?

Qyburn

Telegraph_Sam said:

Does the same [16 / 20 Amp] limit apply to both the RCD and the MCB, or can they differ?

The current rating of an RCD is simply a rating for the maximum current it's designed to carry. Typically 63A or more. It doesn't trip if that limit's exceeded.