Garage electrics

[Multiplex]

Spent a few hours doing my research on this, so would just like confirmation this is okay.

House side:
Garage electrics to be spurred off kitchen ring with 2.5mm SWA (already laid now, 4mm was not available unfortunately).

Kitchen ring is protected by RCBO.

Spur is taken from 13a switched FCU in kitchen.

Garage side:

Garage consumer unit, 40A RCD 1 x 6A 1 x 16A MCB's
http://www.screwfix.com/app/sfd/cat/pro.jsp?ts=31107&id=33248

1mm cable for lights and 2.5mm for sockets. I guess a radial circuit in the garage is sufficient, or is a ring better for any reason?

Question: Is it okay to have a garage CU with a 40A RCD when the ring already is on an RCBO?

Since the cable (9m run) is only 2.5mm, even though its protected by a 13a FCU is there any point in having a garage CU? If I'm mowing the lawn and run over the electric cable is it going to make any difference? Also, if the pond light trips would the garage RCD trip and NOT the RCBO, hence saving the contents of my freezer? Is this how it works?

Thanks,

Simon.

 

[ban-all-sheds]

Garage consumer unit, 40A RCD 1 x 6A 1 x 16A MCB's

I don't think you'll get discrimination between the 16A MCB and the 13A fuse.

I guess a radial circuit in the garage is sufficient, or is a ring better for any reason?

No reason whatsoever.

Question: Is it okay to have a garage CU with a 40A RCD when the ring already is on an RCBO?

No - you won't get discrimination - a fault could trip either, (or possibly both?).

Since the cable (9m run) is only 2.5mm, even though its protected by a 13a FCU is there any point in having a garage CU?

Not really - you might as well just take the cable straight to a the sockets, and another SFCU for the lights.

If I'm mowing the lawn and run over the electric cable is it going to make any difference?

No.

Also, if the pond light trips would the garage RCD trip and NOT the RCBO, hence saving the contents of my freezer? Is this how it works?

No - there's no guarantee of that - you could easily lose the supply to the freezer.

What type of supply earth do you have?

 

[Multiplex]

The earthing is PME (the house is a new build).

If I put a security light on the side of the garage, the type that turns itself on automatically when it gets dark, how would I prevent a blown bulb from tripping the RCBO on the ring main? I.e. I don't want to wake up one morning to find the freezer flooding my laminate flooring!!

Is there any way of guaranteeing this or not really?

Simon.

 

[ban-all-sheds]

The earthing is PME (the house is a new build).

See this http://supplychain.org.uk/phpBB2/viewtopic.php?t=41 for info about exporting PME earths.

If I put a security light on the side of the garage, the type that turns itself on automatically when it gets dark, how would I prevent a blown bulb from tripping the RCBO on the ring main?

I.e. I don't want to wake up one morning to find the freezer flooding my laminate flooring!!

Is there any way of guaranteeing this or not really?

Don't have it on the same circuit as the F/F.

A lamp failure isn't going to result in an imbalance that would trigger the RCD in the RCBO. Does anybody know how likely it is that the surge from a large lamp failing would take out a B32?