3000Tl problem

[edexlab]

We've a system installed 2 months ago 3000 Tl and 240 REC panels on a TT system array earth taken to the Met
which worked well for 6 weeks and then started shutting down
the error/event messages read residual and high discharge currents thus activating the RCMU ,so I've been through all the commissioning tests (Ac and Dc) again

I checked the Ze which was higher than I would have left it
( another electrician working for us installed this system and everything bar this seems ok)

So more rods and its now 26 ohms , rang SMA and spoke to several of their engineers who seem happy its not the inverter after resetting the rcmu and a few other tests
ie voltage between N and PE is low enough and I've sent them the file from the events in Sunny explorer to look at

although they have run out of suggestions as to what it could be ,they have sent us another inverter which due to current situation have not had time to change and
I'm concerned that changing the inverter won't be the answer and will probably end up using a transformered inverter which would eliminate this problem,
but we will try the replacement first
I would be interested to hear if anyone else has had the same problem and what caused it or even any possible theories

 

[SolarCity]

I've not had this specific problem yet. I'd be interested to hear how you get on.

Out of interest, did SMA suggest a Ze reading which they feel should be the limit when installing a TL inverter on a TT system?

 

[edexlab]

No sorry they did'nt
they initially asked me what the Ze was and I did mention that it had been 134 ohms even though I had reduced it to 26 ohms as I thought this may be a contributing factor .
As with any TT system I always try to get the reading as low as is possible before I walk away as I have always thought it could be a problem with the Tls and if the reading is coming down nicely I'll even screw on another rod and go as far as I can with it , I've had one recently where an Electrician has recorded readings of 199 ohms on the cert, I tested and it was 1.2Kohms , he'd left it with the clamp bolt sheared off as well anyhow 10 mins 3 rods later and we had a reading of 23 ohms .

the only limiting factor that I've seen is the N to PE voltage to be lower than 30v this is on the gridforms (compatibility) pdf I don't remember seeing a maximum Ze but when I went there in the seminar 100< ohms was mentioned but I'll have to check my notes to be sure.

 

[edexlab]

Finally got the report back on this inverter and thought I'd post just in case anyone else should have the same problem
It was an internal fault with the RCMU and the associated processor monitoring pcb.