new washing machine trips 3 phase rcd incomer

[graham1]

Hi Chaps,
Got called to an interesting one today, customer has bought a new miele washing machine for a farm building. It is a straight swap for an older machine, trouble is during its cycle it trips the 3 phase rcd 30ma incomer. The socket it is connected to is fed from a single phase breaker connected to L1. Funny thing is if you plug the machine into a socket on a different phase all is ok. Have ramp tested the rcd from both circuits & get the same results (trips around 24mA) but it only evers trips when using first phase!
Any ideas how each phase could affect the rcd differently?
Thanks!

 

[Engineer54]

Probably there is more leakage on L1 phase from other circuits on the same phase, be it natrual or otherwise. That's what you need to find out, by your fault finding exercise...