# Granny flat sub board supply & discrimination of protective devices



## ohiosparky99

Let me grab a dictionary and I'll get back with ya


----------



## electricalperson

can you post some pictures of your irish electrical systems?


----------



## frenchelectrican

10mm² conductors for 63 amp fuse IMO that will not fly with it.

More like about 40 or 45 amps depending on which chart I use.

And I am not sure if you are aware that the UK requirement is simair to your location and it have to be RCD or RCBO protected now per modern codes.

Merci,
Marc


----------



## frank

Fitting a 50 amp type B mcb at the mains will take care of discrimination for you if you are going to use 10mm 6242Y. You need to calculate the possible maximum demand of the flat then apply a Diversity Factor to see if 50 amps has sufficient loading for your 10mm cable. If not you may have to upgrade to 16mm T/E. and use a 63amp type B mcb. Do not forget that since you are adding a seperate dist board you will need to a 10mm 6491X along with you as a p/ll circuit for the earth lead. If you want to be really posh you can also install a time delay type S rcd at the sub main end so as not to have Granny Flat residual earth faults causing neusance tripping to the main dwelling.

Frank


----------



## JNV

yeehaa_electrical said:


> Hi all Im new to to the site hopefully i can learn a few new things and share abit of wisdom when i can.
> I am an irish electrician converting a garage to a granny flat and unsure of a few things. I am going to install a sub board fed from the main board in the house. Irish regs state domestic installations require main neozed fuse to be rated at 63amps. I was planning to run in a 10mm pvc/pvc cable to the sub board fed through a switch fuse for isolation and protection of the cable.
> 
> My question is what is the max size fuse at sub board to provide adequate discrimination and is 10mm cable sufficient?
> 
> The flat is to have a small kitchen with electric oven, pumped shower, possible under sink instant water heater with the usual socket & lighting points etc.


I would fit a time delay rcd at the origin and a 50 amp mcb . Then a 30 ma rcd in the new distribution board in the flat or rcbo's in dist board . There are some ced rcbo' at about £ 15 each cew wholesaler .


----------

