RCBO timing too high

shocked · Mar 4, 2014

Hi All
just done a c/u change fitted with 8 RCBO's and when testing the trip times 2 of the RCBO times were too high (40a 30ma =40.8 ms . 32a 30ma = >40 ms )on X5 ? changed the 2 x trips and retest exactly the same times ?! disconnect the circuits and retest trip times perfect, ok so retest circuits all ok ??! phone control gear and speak to tech it could be the cooker hood (double insulated ) or the w/machine, they don't like them. in my case it was the (40a) electronic shower (32a) combi boiler .
just letting you know
John

jamie-spark · Mar 10, 2014

shocked said:
Hi All
just done a c/u change fitted with 8 RCBO's and when testing the trip times 2 of the RCBO times were too high (40a 30ma =40.8 ms . 32a 30ma = >40 ms )on X5 ? changed the 2 x trips and retest exactly the same times ?! disconnect the circuits and retest trip times perfect, ok so retest circuits all ok ??! phone control gear and speak to tech it could be the cooker hood (double insulated ) or the w/machine, they don't like them. in my case it was the (40a) electronic shower (32a) combi boiler .
just letting you know
John

I asked same the IET same question years ago when I was silly and here is the reply I got. Hope it helps

jamie-spark · Mar 10, 2014

Hi Jamie

Please see the reply from Hager technical manager I received earlier. I recall a megger engineer on the national committee mentioned something similar about the meters being affected by this when loads were in circuit

Hi Richard,

Quick reply as I am in and out of company meetings!!

I hope the following answers the questions. Out of interest, please can you tell me the type of connected load.

I am assuming that your comment "it fails to trip at 150ma (x5) within 40 mS" means it trips, but appears to exceed the maximum time?

This is a well known phenomenon attributed to the load (capacitance) influencing the RCD tester.

This is why the correct RCD test procedure prescribed in GNs states:"The load supplied should be disconnected during the test".

The ESC are currently investigating this, please see attached, page 15 "Influence of connected loads".