Any Advice on tripping problem

[Bornagainsparky]

This one has really got me. I changed a Board on a TT system protected by 100mA RCD everything was fine on the old board except more ways were needed. Put the new 17th edition CU in covered by 100 amp main switch and 2 x 30mA RCD's, everything is tripping.

Carried out IR Tests everything is fine, changed RCD's again, same problem.

Re-checked all cables both visually and again with IR test, no problem up to sockets, switches, cooker outlet, showers etc but as soon as switches are made and loads is applied, both RCD's trip, very frustrating

 

[adamwilliams]

Most likely the heater element is corroding/shorting out due to inproper PH balance in the spa. Disconnect the leads going to the heater and see if the GFCI holds. If so replace the heating element.

 

[malcolmsanford]

Most likely the heater element is corroding/shorting out due to inproper PH balance in the spa. Disconnect the leads going to the heater and see if the GFCI holds. If so replace the heating element.

I think your spot on there, and that borrowed neutral on the light was just a ruse.