Garage supply

[Stephen-d]

Hi all,

Just wondering if some one could help me out on this one, i have a split load RCD board in the house and I plan on putting a new supply to the garage. I am thinking of running a 6mm SWA off a 32a MCB (RCD protected from the board) to a new garage CU, the garage CU will have a;
main isolator switch
20a RCD - radial circuit
6a RCD - lighting circuit

On the radial it will have 5 double sockets with such items, TV, small fridge, dryer and a plug in heater, they won't be used all the time just as and when.
The lighting circuit will just have 1 6ft LED strip light.

The SWA will be clipped direct outside and the cables in the garage will be in conduit. I planned on 4mm for the radial and 1mm for the light.

Is this over kill or am I on the right path?
Any help and advice is greatly appreciated. Thanks

 

[pc1966]

There is nothing especially worrying about your suggestion, but for the cable calculations you need to consider the length and so the impact on voltage drop and/or the earth loop fault impedance to make sure it will disconnect in under 0.4s on a fault to earth.

Sounds like it is just general living/recreational use, but if important (say working with tools, etc) you might want to consider a LED baton light that already has emergency battery back-up included so any loss of mains power does not result in total darkness.

However, if you are in England & Wales then I think adding a new circuit comes under the Part P building regulations and so is notifiable. Realistically you will be cheaper to get a professional sparky in to do that and notify than to try and deal with it yourself (assuming you are not a member of any of the "competent persons" schemas).

 

[Stephen-d]

Thanks pc1966, the swa run is about 15 meters. Thank you for the advice I will take it all into consideration ?

 

[Spoon]

You say

20a RCD - radial circuit
6a RCD - lighting circuit

Do you mean RCBO's.

Just to add to the above, your house CU has RCD protection, so the circuit to/in the garage will have it.
If the above is true then why fit RCBO's? You need RCD discrimination (or Selectivity).

 

[Stephen-d]

Hi spoon, yes the house CU is is a split board each protected by a RCD.
My thoughts were that the garage radial would trip the rcbo (in the garage CU) first not the RCD in the house CU

 

[Spoon]

Hi spoon, yes the house CU is is a split board each protected by a RCD.
My thoughts were that the garage radial would trip the rcbo (in the garage CU) first not the RCD in the house CU

No mate. I'm guessing it would be a flip of the coin as to which trips first, as they are the same type.
If you have a spare way in your house CU that is not on a RCD, you would always fit a 32A breaker (as the SWA cable doesn't need RCD protection) and then have RCBO's in the garage.
Or just have normal breakers in the garage and use the house RCD for protection.
If you want to make it a bit safer then you could fit an small emergency light, as mentioned above.

 

[Stephen-d]

Thanks spoon it makes sence now. There is no spare non RCD ways on the board, so the circuits in the garage would have to be on MCB, so as long as the disconnection time and the Zs meet the requirements this would be ok?

 

[Spoon]

Thanks spoon it makes sence now. There is no spare non RCD ways on the board, so the circuits in the garage would have to be on MCB, so as long as the disconnection time and the Zs meet the requirements this would be ok?

Yep, but as mentioned above, this is a new circuit so it falls under Part P and is notifiable.

 

[Stephen-d]

Much appreciated, thank you!

 

[telectrix]

To notify, or not to notify, that is the question:
Whether 'tis nobler in the mind to suffer
The slings and arrows of outrageous NICEIC membership,
Or to take Arms against a Sea of LABC Red Tape,
And by opposing end them: to die, to sleep;
No more; and by a sleep, to say we end
The heart-ache, and the thousand natural shocks
That arise from kitchen fitters and builders electrics,,
That Flesh is heir to? 'Tis a consummation
Devoutly to be wished. To die, to sleep, no more.

 

[Stephen-d]

To notify, or not to notify, that is the question:
Whether 'tis nobler in the mind to suffer
The slings and arrows of outrageous NICEIC membership,
Or to take Arms against a Sea of LABC Red Tape,
And by opposing end them: to die, to sleep;
No more; and by a sleep, to say we end
The heart-ache, and the thousand natural shocks
That arise from kitchen fitters and builders electrics,,
That Flesh is heir to? 'Tis a consummation
Devoutly to be wished. To die, to sleep, no more.

Late reply sorry but it was notified, I found someone who certified and registered the work ?