Nuisance tripping solved on PV install. Not sure why?????

[Dan59H]

Sorry for the Lenghty post, in summary. swapped RCD's on a split load board it stopped trippng. Why's that?

Got called back to Air Source Heat pump install that was experiencing nuisance tripping 2 days after a PV install.
It was a split load Eaton board with 2 of the heating circuits tripping on the one side and 1 other circuit and the sockets on the other side,
tripping the same RCD.
Had a look at all the terminations on the heat pump side, they were ok. I treid the sockets and it was every socket that was tripping so thought it was unlikely to be an equipment problem. I thought it might be a faulty RCD so I swapped them over to try and get the same results. Suddenly, no tripping?
The PV installers had chopped things up inside the board a bit, to get there stuff in and I noticed they had a bit of a flash, you can see the blacking but can't see how if it had been damaged that would stop the tripping once i swapped it?

Any thoughts my esteemed friends?

 

[telectrix]

for .a start, in pic 1. that CU wants stripping out and re-doing. it's a monkey's abortion

 

[Dan59H]

I know, preaching to the choir, any thoughts on the tripping?

 

[telectrix]

pssibly an over -sensitive RCD. did you test it before swapping ?

 

[Dan59H]

No didn't ramp test it, once I swapped it it didn't trip at all

 

[Octopus]

Get the PV installers back.

 

[BruceB]

As suggested above, probably one rcd more sensitive than the other. A 30 mA rcd is within spec tripping anywhere between 15 mA and 30 mA.

You may also have cured a minor earth leak in that rats nest just by moving wires around.

 

[Gavin A]

is the PV installed to a shared RCD on the split board?

if so the answer is pretty simple - solar PV inverters ALL result in a degree of earth leakage, usually in the 5-10mA range, but can be higher, particularly with transformerless inverters, and particularly when the panels and roof are wet such as at dawn when they're covered in dew.

They should never be installed to shared RCDs precisely because they are prone to cause nuisance tripping as it effectively reduces the RCD to a 20mA RCD... but 30mA RCD's can actually be anything between 15-30mA in reality, so there could only be a few mA available on a lower rated RCD after the inverter is connected. Which would be why swapping one 30mA RCD for another can appear to solve the problem.

 

[SolarCity]

Further to this, PV installed on a shared RCD can be safety issue. The inverter could be feeding back on to all the circuits which share the same RCD, rendering the RCD reaction times as worthless.