No Discrimination

[normanton]

Evening guys,
Query with discrimination. Main DB with 30m/A RCD feeding another sub board with 30m\A RCD. The RCD in the main DB is tripping out before the sub board RCD. Am I able to change the Main DB RCD to a type S? (All that Main RCD is feeding is two sub boards, twin and earth fed in an office. Thanks in advance..

 

[Sintra]

Is the t&e surface clipped or buried?

 

[westward10]

What is the earthing system. It's selectivity these days

 

[normanton]

T&E is in the stud partitioning and under floor boards. Earthing System is PME....

 

[Deleted member 105166]

If the final circuits in the two sub mains are all RCD protected, do you even need the upstream RCD?

 

[Sintra]

Then unless the cable is in earthed metallic protection or more than 50mm from the surface if in a wooden stud or in a metal stud then it requires additional protection by a 30mA RCD. You can’t get a type S 30mA RCD.

 

[westward10]

How long do you think the rcd in the main board has been there.

 

[normanton]

#5 You wouldn’t need the main RCD or you wouldn’t need the sub RCD?
It’s a two year old installation by the way. Was thinking about changing the main 30m/A RCD to a 100m/A type S but obv can’t because it need additional protection. Hmmmmm

 

[westward10]

If it's only a couple of years old sounds like poor design for a submain to require additional rcd protection. If it had been pre additional protection for cables in walls you may have had an argument although tenuous for removing it but as it stands it would be a bad idea.

 

[normanton]

So any suggestions to stop this nuisance tripping? Think it’s a big fat no haha

 

[westward10]

You need to know what is causing the tripping fault or combined excess natural leakage. Is it both supplies or just one. Do you have an earth leakage clamp meter.

 

[davesparks]

So any suggestions to stop this nuisance tripping? Think it’s a big fat no haha

Yes, replace the distribution circuit with a different cable type or route so that the rcd protection is not required.