tripping RCD on TT system

Got abit of a problem, fitted system with Power-one 2000 inverter via mini CU. Being TT,(overhead supply) fitted 100mA RCD. Fine for a day or two, then starts occassional tripping. Replaced RCD with type S, problem persists. Double checked all connections - can't find anything wrong. So I'm abit stuck for ideas as to what is causing problem, how to prove it, and possible solutions, though suspect it's something to do with incoming supply rather than PV work? Did phone Power one - they assure me that the inverter has 2 layers of protection to prevent earth leakage, so unlikely candidate? VOELD doesn't trip, but is so old it probably doesn't work!!

Is that inverter suitable for TT? Have you only used the RCD to protect the inverter and not the other circuits?

---------- Post Auto-Merged at 17:28 ---------- Previous post was made at 17:27 ----------

Ive done a few that have had a leakage of upto 97mA, but they were 3phase!

don't think my meter is sensitive enough. My suspicion lies with supply, but can't think whether problem with incoming supply can cause RCD to trip (head so full of PV I've forgotten)

---------- Post Auto-Merged at 17:41 ---------- Previous post was made at 17:33 ----------

Is that inverter suitable for TT? Have you only used the RCD to protect the inverter and not the other circuits?---------- Post Auto-Merged at 17:28 ---------- Previous post was made at 17:27 ----------

Ive done a few that have had a leakage of upto 97mA, but they were 3phase!

Click to expand...

Inverter manufacturer claims 2 levels of protection to prevent leakage within the unit. Circuit is all of about 4 feet long to mini CU with RCD which in turn goes straight to meter tail blocks. Only other possibility that I haven't checked for yet is damaged cable, which is a possibility.

Transient voltages can trip RCDs

Is it an overhead supply?

bad joint up pole can be the culprit

Circuit is all of about 4 feet long to mini CU with RCD which in turn goes straight to meter tail blocks

Click to expand...

can I assume you have that the wrong way around?

the circuit comes from the 'tail blocks' to the CU.

ok, from what I can get out of these manuals it appears that an RCD of at least 100mA should be used under any conditions for a power-one TL inverter,

it also seems on reading some other manufacturers manuals that they are also stating 100mA RCDs to be used for TL type inverters,

Ive only skim read them so my apologieses (???) if Ive got it wrong.

Im trying to find the actual manual now canoey, Ive just found a scrap of paper I wrote on a while back,

I got a stack(well a few) different install manuals for some of the inverters Ive done, but missus decided to tidy up a while back, so, you know....

Transient voltages can trip RCDsIs it an overhead supply?

bad joint up pole can be the culprit

Click to expand...

this is what I am suspicious of as it randomly trips during the day about once a day!!

RCD fitted is type S 100mA, and does not trip out on start-up of inverter which is where I have seen problems before.

Think I have sorted this out now ray

Get to job this morning - nice bright sunny day so panels are well upto some fun.

RCD had tripped out again, so re-set and go look at inverter, which duly fires up after 180s and trips RCD straight out.

Go back inside and remove earth at CU fire up again - perfect, 2kW from 2.16 kWp system. Touch earth to earth bar - trips staright out. Check out RCD seems to be working fine bar ramp test is 65mA. Test IR >299Mohm all conductors. Attach digital multimeter between earth and earth bar - trip... Reset system and wait for it to start, as soon as the sun peaks out from behind cloud, and system rises to measured 5mA - trip???

So leave earth out again and just run system for 30 mins - no problem, it's a windy day here in sunny Devon so overhead cabling getting a good shake. Still no problem. Notice it's not VOELD but early 100mA RCD on existing electrics, so this seems to rule out incoming supply issues. (system is TT, Ra 21 Ohm with bonding attached)

Getting very confused now as I can't find anything wrong with any part of the system. So take wander out to van to inspect the supply of come-in handy MCBs RCDs etc etc. Dig out Hager 30mA RCD on grounds that it may be a 'make' issue.

Fit hager unit - struggle to see bus bar in bottom of Newey MCB (missed it 3 times. Finally get system fired up and hey - presto it's all working with the sun out to play.

Conclusion :-

1/ Control Gear RCds don't like inverters????

2/ We missed busbar and had poor contact between MCB clamp and busbar.

I think it was possibility 2 - unfortunately I didn't notice if it was clamped properly when dropping bus-bar out to change RCD. In my defence the CU is at the back of a fairly dark cupboard. This option I feel fits better with the whole scenario of the more power the panels are making, the more often it trips RCD, and problem was escalating ie tripping more often. Didn't observe any witness marks on bus-bar though. The customer had previously observed that it seemed to trip RCD when sun was out and also fits with the scenario that the system would happily start-up every day and fail around mid-morning (south facing array).

Any way, fingers crossed, no more e-mails from customer so-far ray rayray

So did you leave it with the Hager 30mA RCD or put the original 100mA RCD back?

left Hager in and :run

Should have put other RCD back in to prove point, but time is money and I had better things to be doing like quotes and jobs and paperwork for PV so didn't want to waste any more time than I already had.

yep, but with Hager Type S this time just to make sure :^O