Washing Machine trips RCB - I think!!

[Captain Mike]

I'm not an electrician but I do have a problem with an RCB that keeps tripping. The RCB is incorporated in an MEM LB6301 Consumer Unit. In the last 6 weeks, we have suffered sevaral trips of the RCB during the time when the washing machine has been operating. Having reported the fault to our electrical appliance insurers, an engineer visited and replaced the washing machine motor. The machine has since been used on 3 occasions without a problem but now on the fourth usage the RCB has again tripped right at the very end of the cycle just as a relay sounds to operate and switch off the cycle. Before sending for the engineer again, does anyone have any suggestions as to which direction to point him in or which tests/checks he should be carrying out?

When I say "trip", the RCB does not move from its upward position but has to be manually moved from the up to the down and then back to up to restore power.

 

[Malc]

I think that in some RCDs the handle doesn't move so as to stop you holding it on when it wants to trip.

You don't say what is the trip current of the RCD?

Water and RCDs is a bad mix. Things like water heaters can have a standing leakage so the trip may be caused by having the HW tank on as well the washing machine (or the oven or the grill as all elements can leak earth current).

BTW is there any sign of water leaking that could be causing the problem? You wouldn't need much.

As for tests the obvious is to measure the earth line current with a sensitive clamp on meter while the washing machine goes through its cycle. Whatever causes a jump in the current must be suspect. Or if there is a large current to start with, say from the EMC filter at the cable input.

 

[Captain Mike]

Thanks Malc
It looks like 30mA

 

[Malc]

I thought it might be 30mA. I enventually gave up on the 30mA in my consumer unit and changed it for a 100mA. The I got 30mA plug in RCDs for the sockets used in the garden. The 30mA was very prone to nuisance trips and it was always a worry that the freezer would be off when got back from a holiday .

I measured my trip and found it went at about 25mA, and the HW tank heater was about 7mA of leakage AFAIR. Anyway, turn on the HW tank, the dishwasher and the washing machine and the RCD was on a hair trigger.

 

[plugwash]

I thought it might be 30mA. I enventually gave up on the 30mA in my consumer unit and changed it for a 100mA.

bad boy

The I got 30mA plug in RCDs for the sockets used in the garden. The 30mA was very prone to nuisance trips and it was always a worry that the freezer would be off when got back from a holiday .

thats why a freezer should be on a dedicated cuircuit the non-rcd side

I measured my trip and found it went at about 25mA, and the HW tank heater was about 7mA of leakage AFAIR.

7ma thats rather high either replace it or put it on the non-rcd side and give it a suplementry 4mm earth cable back to the CU

Anyway, turn on the HW tank, the dishwasher and the washing machine and the RCD was on a hair trigger.

mmm sounds like it with the way your HW tank was

 

[Malc]

Bad boy? Why? I'm on PME which AFAIR does not need any RCD, unless that has changed. True 30mA is the ideal level as that is the maximum guaranteed not to kill you, probably. However, let's be practical. The choice was between a huge rewire job or going to 100mA trip, which still offers quite a lot of protection, plus 30mA trips for danger areas. Add to which my childern are all that much older now so there is not some much need for a 30mA trip (which I originally put in BTW).

In hind sight, or were I doing a big rebuild job, then I would probably give the freezers, washing machine, dishwasher, HW tank, cooker, all a non-rcd or 100mA rcd circuit, and reserve the 30mA circuit for the rings etc. But rewire the house just for that? I don't think so.