RCD on a TT system

[andyww]

I believe a TT system must be protected by a 100ma RCD - if it is protected by a 30ma RCD could this cause nuisance tripping?

 

[Spudnik]

If you are installing a CU to the 17th Edition, then 100mA upfront is not required PROVIDING the new CU is of all insulated or class II construction.

 

[andyww]

Thanks jason - not installing a CU - customer has just moved into a new house and the CU is 15th or 16th edition with 30ma RCD main switch already in place (unfamiliar make - by Schneider Electrics). The RCD trips when the washing machine comes towards the spin cycle - I've tested the machine (line to earth / neutral to earth continiuty & ins resistance) and can't find any fault. It's a four bed detached house with only one ring circuit - and earthing is TT (I've advised they should contact EDF for a PME upgrade) - I'm wondering if the cumulative effect of all the household appliances being on one circuit could be causing the tripping - lots of small earth leakage adding up to over 30ma?

 

[Spudnik]

Thats quite possible, however, i would maybe be looking at the pump of the WM.

Normally on a spin the pump operates at the same time to empty the drum, and it could be that breaking down which wouldn't necessarily show up with an Ins test.

 

[andyww]

OK - so being a relatively new electrician I haven't had any experience of testing appliances - how would I establish if it is the pump?