C
comptonspark
Hi have a problem which I hope that somebody can shed some light on.
New install on existing TT supply, with two DBs fed from an SWA sub main with 100mA S type RCD and 100A switchfuse at the origin (no other loads on supply).
DB 1 is for a new install and all circuits are protected with 30mA RCDs. DB2 is a new board for a number of existing circuits again all 30mA RCD protected except for two further sub mains which are just on MCBs with 30mA RCDs at the far end. Both boards and sub mains etc test out ok and 30mA RCDs all trip in the required times.
The problem occurs when DB1 has all circuits on and some load (mainly IT equipment and some lights (its a small office) and DB2 is commected with the main switch on and the two RCDs on but all MCBs are off. After a while the 100mA S type RCD trips. It seems ok with only one RCD on but not both. Can also get some MCBs on before the S type trips.
I've tried checking connections, checked wiring, retested IR of circuits, but to no avail, I still can't seem to find out what is causing the trip. Even clamped the tails at the S type and only get 10mA to 15mA leakage and the max hold function dosen't record any larger values.
So anybody got any suggestions? I was thinking of getting another S type and trying this otherwise I'm scratching my head on this one.
thanks
New install on existing TT supply, with two DBs fed from an SWA sub main with 100mA S type RCD and 100A switchfuse at the origin (no other loads on supply).
DB 1 is for a new install and all circuits are protected with 30mA RCDs. DB2 is a new board for a number of existing circuits again all 30mA RCD protected except for two further sub mains which are just on MCBs with 30mA RCDs at the far end. Both boards and sub mains etc test out ok and 30mA RCDs all trip in the required times.
The problem occurs when DB1 has all circuits on and some load (mainly IT equipment and some lights (its a small office) and DB2 is commected with the main switch on and the two RCDs on but all MCBs are off. After a while the 100mA S type RCD trips. It seems ok with only one RCD on but not both. Can also get some MCBs on before the S type trips.
I've tried checking connections, checked wiring, retested IR of circuits, but to no avail, I still can't seem to find out what is causing the trip. Even clamped the tails at the S type and only get 10mA to 15mA leakage and the max hold function dosen't record any larger values.
So anybody got any suggestions? I was thinking of getting another S type and trying this otherwise I'm scratching my head on this one.
thanks