More RCD probs

[bhmike]

Just installed 62kW on a roof along with 38kW on ground.
The 62kW feeds 3 X Tri-power 17000TLs Then into a TP&N board via 3 X 40A mcb out through a 300mA incomer.
50mm 4Core sub-main (45 metres long) to a 400A Panel board. The sub-main is protected by a 300mA S-type RCD (on a farm).
The S-Type RCD protecting sub-main trips (not immediately) if more than 2 inverters on. The 300mA RCD on TP&N board is fine.
All RCDs are AC type as SMA say no risk of DC leakage.
What I don't get is why the S type is tripping and not the other.
Probably some highly technical reason for this - any ideas anyone?

 

[DurhamSparky]

Faulty???

 

[bhmike]

No, tried 2

 

[yellowvanman]

You sure you're cable is OK? Does it make any difference what 2 inverters are on?

 

[DurhamSparky]

hmmmmm.........

you obviously sailing close to the wind on MA leakage... cqan you get rid of the 100ma rcd and use the 300ma as protection and locate the 100ma upstream from your invertors...??

im unfortunately guessing as i dont install PV and not fully upto speed with what the regs are for it...!

 

[bhmike]

SWA cable tests OK for insulation etc. Makes no difference which inverters are on.
If all 3 inverters start up together it trips out within a few seconds.
If I stagger the start-up it can take up to 10 minutes before it trips.
If 2 or less all seems fine.

 

[bhmike]

No 100mA RCD there.
The S-type 300mA protecting sub-main is tripping (has to be there as is on a farm)

 

[yellowvanman]

The S type that is tripping is protecting other circuits? Can you isolate all the othr circuits and run just the inverters? If so then as has been said you may have a 'leaky' other circuit and the inverters are pushing the 300mA limit at the mains.

 

[DurhamSparky]

sorry im reading words that dont bloody exist....! been a long day and will be a long nigh..!

 

[bhmike]

No this is a dedicated sub-main.
My thinking is if the inverters were causing the problem why is the 300mA RCD on their TP&N board not tripping.
Maybe the output from the inverter sub-main coming up against grid at panel board is causing some disturbance.
Between panel board and grid is a G59/2 cut-out.
I just don't get why the S-type is tripping and not the ordinary 300mA

 

[yellowvanman]

You may have fixed it by now, but my next suggestion would be to swap the positions of the delayed and non-delayed RCDs and see if the tripping RCD moves, if it does then its something to do with the RCD if it doesn't then there is a problem between the 2 boards.

 

[SibertSolar]

Might be coming into this a bit late (on hols) but you might need to bear in mind that just because SMA say a Type B isn't necessary doesn't mean an AC type will suffice. A Type A is most pobably the minimum required type (germany do not use AC type at all - their default is Type A - check with SMA if you are not sure). Type AC will not cope well with any DC leakage currents....