RCD tripping on split board, strange one

[vini]

I'm not even sure if I can properly explain this one. When the shower is switched on the RCD (1) on the other side of the board trips. The shower continues to work fine and when they come out they reset the RCD until the next person needs a shower.

When the hoover is switched on and plugged into the ring on RCD (1) side of the board the RCD (1) trips, but when the hoover is plugged into the ring on RCD (2) it is fine and works. Apparently the same thing happens with the kettle, sometimes. Other appliances are fine.

They did have a fire about five years ago and the place was partially rewired. A split board was put in about 2 years ago

IR tests are fine.
Neutrals are all correct.
Ring mains are not crossed.

 

[telectrix]

N-E fault on 1 of the RCD1 circuits. prossibly very low reading if you take out the L and N legs of each circuit in turn from CU and IR test,

 

[7029 dave]

IR test, did you test each circuit individually on that side of the rcd, if so what readings did you obtain.?

 

[Ziggie]

As an aside, I had an RCD trip some times on a circuit with a freezer on it when I used a DIY tool or lawnmower in the RCD socket. The trip probably caused by earth leakage current from the freezer which is only operational when the freezer is actively cooling. I removed the RCD and used an extension cable with an RCD and there was not any tripping.

so some RCDs are more sensitive even though they have the same spec.

 

[Strima]

Could also be a poor neutral connection on the supply side. Have you ramp tested the RCDs?

 

[littlespark]

so some RCDs are more sensitive even though they have the same spec.

thats true.
All are marked as 30mA, but when ramp tested some could be 29, 26, even as far down as 19mA

 

[vini]

Mystery solved. An extension cable plugged into a garden shed socket leading out to the garden to feed a water pump in a pond. The extension cable (socket end) wrapped up in a poly bag, left outside in Scotland. Sometimes dry, mostly wet. Never trust customer's explanantion of what is going on in their house holds.

 

[Rockingit]

Rule of thumb for RCD faults that 'just started to happen' is rain, DIY or faulty appliance.

 

[Ziggie]

Mystery solved. An extension cable plugged into a garden shed socket leading out to the garden to feed a water pump in a pond. The extension cable (socket end) wrapped up in a poly bag, left outside in Scotland. Sometimes dry, mostly wet. Never trust customer's explanantion of what is going on in their house holds.

Thanks for the update - very helpful!