Solar trips rcbo c16

[newfutile]

There are 2 inverters feeding into a dorman smith C16 rcbo , every time I visit this site (communal area power) it has tripped.

it switches on first time and never trips when im on site (though there is cloud cover today).

all the correct DC and AC isolators are present the inverters are a:

Shenzen JFY-TECH JSI-2500TL max power 2000 W 13 amp max current
SUNNY BOY SB 5000TL-21 max power 4600 VA 13 amp max current

i am unable to tell what solar panels are fitted, i also don’t know if the (RCD) Residual Current Device or the overcurrent part of the rcbo has trippped.

anyone have any idea ?

 

[kropaske]

Potentially you have 28A on C16 breaker. It will trip eventually. If you visited the site in the winter months, did the tripping occur?

 

[loz2754]

I'm no solar expert, but if the two inverters are feeding into the same Rcbo at their full current output combined, that could be reason it's tripping. 2kW added to 4kVA translates to around 28 amps.

 

[newfutile]

I have been back to this property today and once again found it tripped, the sma inverter appears to leak a great deal to cpc.

As the wiring is surface/tray and run in 4 or 6 mm twin and earth I propose to change to a C25 mcb and I'm considering a 100ma rcd double pole in it's own enclosure.

I seem to remember that rcbo should not feed an inverter unless it's double pole, can anyone confirm this?

 

[davesparks]

Why is RCD protection required and is there an RCD at both ends?

As you've suggested a 100mA RCBO I assume the RCD is for fault protection only and not additional protection?

I can't see that 25A overcurrent protection is appropriate either if the total load is 28A, surely that would need 32A protection?

 

[newfutile]

I think your right an a 32 amp mcb will be required , its a TN system with a ZS at the inverter isolator of 0.22 ohms . So fault protection is via the MCB and 100ma cant be additional protection in the traditional sense.
the only reason i thought of 100ma was because of the already high leakage currents .
i now have the installation manual and it appears to monitor the leakage current internally.

 

[davesparks]

I think your right an a 32 amp mcb will be required , its a TN system with a ZS at the inverter isolator of 0.22 ohms . So fault protection is via the MCB and 100ma cant be additional protection in the traditional sense.
the only reason i thought of 100ma was because of the already high leakage currents .
i now have the installation manual and it appears to monitor the leakage current internally.

But what would that 100mA RCD protection be for? What is the reason for it having 30mA RCD protection at the moment?

Is there a socket in the circuit? Is the cable buried in the wall less than 50mm deep? Is it in a bathroom?

Just because there is protection in the inverter it doesn't necessarily mean you don't need to install any.

A solar PV circuit is different to most other circuits we normally work on. Most circuits connect to one source of supply at one end of the circuit. With solar PV the circuit is linking two sources of supply together, so an RCD installed at one end of the circuit may not achieve anything as the when it trips the circuit could remain live due to the other source of supply still being connected.

 

[newfutile]

It’s not buried it’s all surface in cup and on tray ,no other accessories other than meters and isolators . The only reason I can think is because the original installers did not understand fully what they was doing hence the C16 RCBO being single pole and underrated for the actual current.
on a side note rcbos must not be able to work with reverse current leakage .

 

[littlespark]

Are you sorting this while you’re there?

 

[newfutile]

Yes I will be , it’s probably just as easy to fix it as to code it

 

[pc1966]

A friend of mine had a solar PV system fitted and it also tripped on a 30mA RCD. I think the fitters just put it in as monkey-see-monkey-do sort of process as it was not needed (SWA to outdoor inverter box) and the manufacturer suggested over 100mA and even a selective one to avoid false trips.

It is common in the EU to have TT systems so maybe the talk of using a 100mA RCD, etc, is all about meeting disconnection in that sort of a system while not taking out something like a 300mA delay incomer?

 

[timhoward]

Could it be the case that the clamp meter readings are in fact measuring the total leakage of circuits upstream that are using the inverters output rather than the inverter itself leaking current to earth?
Have you tried readings with no load (from grid or PV) other than the supply to the inverters and the DC isolator(s) turned off?

 

[newfutile]

I have now changed for a 32 amp mcb and I'm happy to report that the power has stayed on and for the first time in 5 years we are generating power.

 

[newfutile]

I have also used a clamp meter and determined that the sma inverter is the cause of the leakage, this appears to be proportional to the current generated .