Garage CU and RCD in series

[Matthew]

Evening all - got a question that i think i no tje answer but need some assurance!!
Putting a sub main (garage CU) with standard sockets and lights.
Feed to garage CU from suitable MCB in main board that IS RCD protected.
Now........testing ... Most garage CU come with RCD, my understanding is RCD in series a pain so looking for the correct way to test - or is it easier to get a sub main with a 100A main switch no RCD? Thanks

 

[buzzlightyear]

what is the cable to the garage ?what system from DNO ,water ?

 

[Matthew]

Nothing yet as haven't installed but probably 6mm T&E - garage is attached and very short run from DB to garage

 

[Matthew]

TNC-S no water

 

[A032701]

you could feed the garage of a 32/40 amp mcb that isn't rcd protected then your garage has its own rcd protection.
the mcb in the main cu would protect the 6mm from overcurrent

 

[telectrix]

agree. as long as the sub main feed don't need RCD protection ( i.e. SWA or T/E surface, then just RCD the garage end.

 

[Matthew]

Thanks both - problem is the main DB is split load 2xRCD board so all MCBs are RCD protected gggrrrrrr!

 

[Wilko]

Hi - If it's attached, maybe simpler to extend the existing circuits into the garage?

 

[Matthew]

I need 2 x new circuit and would rather leave current wiring alone

 

[TJ Anderson]

Thanks both - problem is the main DB is split load 2xRCD board so all MCBs are RCD protected gggrrrrrr!

No biggy really. Just put standard double pole main switch in the garage DB as you have the RCD protection upstream. There's loads and loads of garages like that.

 

[A032701]

Thanks both - problem is the main DB is split load 2xRCD board so all MCBs are RCD protected gggrrrrrr!

i have a mk sentry metal db dual split rcd and just slid the rcds and mcbs up the din rail to make room for an mcb between the main switch and the first rcd. put a short buzz bar to connect it.

 

[Pete999]

Evening all - got a question that i think i no tje answer but need some assurance!!
Putting a sub main (garage CU) with standard sockets and lights.
Feed to garage CU from suitable MCB in main board that IS RCD protected.
Now........testing ... Most garage CU come with RCD, my understanding is RCD in series a pain so looking for the correct way to test - or is it easier to get a sub main with a 100A main switch no RCD? Thanks

Yes Change to Main Switch

 

[Matthew]

Thanks all for your advice - a couple options there. Really useful .

 

[Matthew]

How would you record the install? MWC for the main DB to garage DB ( assuming using MCB that is there already and has 6mm cable just re-routing) and EIC for garage DB

 

[buzzlightyear]

How would you record the install? MWC for the main DB to garage DB ( assuming using MCB that is there already and has 6mm cable just re-routing) and EIC for garage DB

try a EIC cert for that, not a minor .

 

[Fitzy]

How would you record the install? MWC for the main DB to garage DB ( assuming using MCB that is there already and has 6mm cable just re-routing) and EIC for garage DB

House CU to garage is “new circuit” and garage DB is a “new CU”, so both require an EIC to be issued and LBC notified.

 

[Deleted member 26818]

i have a mk sentry metal db dual split rcd and just slid the rcds and mcbs up the din rail to make room for an mcb between the main switch and the first rcd. put a short buzz bar to connect it. View attachment 47518

How does the RCD like sharing the Neutral with the stand alone MCB?