PV Circuit Breaker Tripping

[buzzlightear]

Gutted to have missed out on a reasonably sunny day of solar production yesterday because the circuit breaker linked to my PV system tripped.

Although it was breezy, there wasn't a powercut - I know because it wasn't necessary to go round the house resetting umpteen digital clocks and appliances!

What confuses me (and why i'm posting this message on the forum) is that absolutely no power was produced at all, suggesting that the system might have tripped during start up (7:52am according to Sunnybeam Display). 

Once the circuit breaker was reset on my return home the system seemed to start up without any issues to capture the last few moments of daylight - a whopping 98wh!!

Is this a common experience amongst members? Does anyone have any idea what could cause the PV circuit breaker to trip?   

I'm starting to understand why some people might have been inclined to invest in remote monitoring equipment...

[BruceB]

Unusual for a circuit breaker to trip.
Do you mean a mcb, rcbo or rcd?  And what rating(s) is it?

[Automan]

Unusual for a circuit breaker to trip.
Do you mean a mcb, rcbo or rcd?  And what rating(s) is it?

Indeed,

If not sure, can you post a picture of it?

Or make and model number...

Automan.

[buzzlightear]

Here's a picture of the board and breakers, which I hope will help. It was only renewed in March. All breakers appear to be marked as 30mA.

I know nothing about electrics!

[Justme]

I thought PV was supposed to be connected via a 100mA not a 30mA?

[SolarCity]

The issue could be one of two things.

It could be overloading if you are running a 4kWp system although this is is very unlikely, especially at start up.

The most likely cause is the 30ma RCBO.  This needs to be replaced with a 100ma RCBO instead.  If you're running a 4kWp system then it should be upgraded to a 20A also.

[BruceB]

Those are all rcbos.  As per the previous post they can trip in 2 ways, overcurrent or earth leakage.

It probably went because of earth leakage >30mA, since a 16A breaker will not trip instantaneously even with say 20A flowing through it.

The instruction manual for the 3800 is silent on rcds.  Unless you need one because the cables are buried <50mm deep in a wall then I would normally not use one.  In your case the way to do that would be to substitute the rcbo foir a mcb.  And I agree with the previous poster that 20A is more appropriate than 16A for the mcb protecting the cable for that inverter.  If you have to have a rcd because say you have a TT installation, then try a 100mA rcbo rather than 30mA (if Crabtree do them).

As you say you are not very knowledgable on electrical matters can you get your installer back to look at it under the guarantee?.  If he changed the CU also then even more reason to get him back to investigate.

Regards
Bruce

[buzzlightear]

The issue could be one of two things.

It could be overloading if you are running a 4kWp system although this is is very unlikely, especially at start up.

The most likely cause is the 30ma RCBO.  This needs to be replaced with a 100ma RCBO instead.  If you're running a 4kWp system then it should be upgraded to a 20A also.

Thanks for replies. From what's been said I guess I'm looking for an rcbo which states; C20 100mA on the front?

The consumer unit was replaced by an electrician after PV install. Not a PV installer issue on this occasion. I'll get it looked at again. Thanks for your help.

[BruceB]

That would do it, but I do not think Crabtree make a 100mA rcbo

The only one I could find on a quick google search was a Schneider 100mA rcbo which is 2 modules wide rather than your single width.

You really need to understand from your electrician why there is a rcbo there.  Did he add it?  If there is no good reason, then get rid of it.

Only just noticed that those rcbos are all C type rather than B type.  Not against the regs but an unusual choice for a normal electrician to make.  On the lights it should stop them tripping when a bulb goes.

Regards
Bruce

[SolarCity]

I agree with everything that Bruce has said.  To be fair to the electrician, most of them are not aware of the issue with inverters and RCBOs.  I'm also surprised to see type Cs used.  Unusual in domestic installs but not exactly an issue as long as the Zs readings came out ok.

[GavinA]

personally i'd not install a 20amp MCB unless you've got permission to go above 16amps, otherwise I concur.

[Automan]

How about replacing the PV breaker with a normal Class "B" MCB with the same current rating?

Before changing to a 20amp I would check cable size and run length plus details of any switchgear in the route to the inverter.

Or of course do nothing...

Perhaps it will not trip again...

Automan.

[MrAmps]

The transformerless invertors by their nature of construction have a high built in earth leakeage and this can be up to 20mA in some cases, if a 30mA RCD is then placed on the AC side and there are other items on the the House circuit that have a high earth leakeage ie computers ect then the RCD will almost certainly trip at some point. Even putting it on its own RCBO may not stop this as they can often trip as low as 25mA depending on the quality of the RCBO.  There is no requirement to install an RCD unless the AC cable is burried less than 50mm from the surface or it is located in the bathroom !!! On a TT system that is fitted with a 17th Ed Board ie with 2 30Ma RCDs I would fit a seperate 1 way unit fittted with a 100mA RCD.