Correct discrimination?

[Engineer54]

anyway you shouldn't have two rcd's in line unless they are of different rataings (I an)

Not even then, unless your talking about 500mA upstream and 30mA downstream. I've even seen that arrangement trip out together, if the leakage has been excessive...
The only sure way of achieving discrimination between RCD devices is by time delay!!

 

[dixon9]

Do you have 3 neutral bars in the house CU? If so then put in a 100mA Time delay S type RCD (bit pricey though) and run the shed/cabin supply mcb off this....you could then use a 30mA RCD in the shed/cabin and have discrimination - should a fault develop in the shed/cabin then only the 30mA RCD in the CU there will trip without taking the house out. The cable run from the house to the shed/cabin is also RCD protected.

 

[leokiss]

I've had a proper look at job today I think I'm going with split tail small enclosure with double pole isolater feeds 32amp mcb which feeds armoured to cabin where I'll fit the small garage type enclosure 63amp 30milliamp rcd switch feeding 20 and 6 amp mcb. Cheapest way and easier of options to install. Cheers for feedback

 

[telectrix]

sounds like a plan. just need to decide whether to use 2 coreSWA using armour as cpc or 3 core. ( or even to TT the garage ). i would deffo use 6mm to allow for possible increase in demand.