RCD minimum times...

[silentboarder69]

Hi,
I'm investigating an intermittent problem in a flat. Every once in a while the RCD trips. The tenants have narrowed it down to one circuit, the electric hob. However, it never trips whilst I'm there, even after pouring water on the hob. I've carried out 500v insulation resistance tests, and all OK. I then carried out a ramp test and the RCD trips at 21mA. Is this too sensitive?
The RCD did trip once whilst I was there, but wouldn't trip again.

 

[telectrix]

intermittent fault on one of the elements when warm. only way is to track it down by trial and error. turn 1 element on at a time till you find the 1 that trips the RCD. 21mA is not bad. there could be a small leakage elsewhere.

 

[Deleted member 26818]

Black iron heating elements absorbe moisture which can cause earth leakage.
You will also find leakage to earth when the elements are on their way out.
I would switch on each element and look for bright spots which would indicate wher a fault is developing.
If there is no bright spot, then it is most likely just moisture absorbtion.

 

[tony mc]

Do you have a earth leakage clamp meter to see how much its leaking could be if you only have 1 RCD on the CU its the total amount thats sometime putting it over the 21 mA with other appliances switched on.

These faults can be time consuming and frustrating to say the least maybe a RCBO on that circuit if possible to minimise inconveniance!