Basic garage rewire and CU installation.

[Coliander]

I'm about to start the process of refreshing my single detached garage. Currently the power to the garage is supplied from an RCBO in the house, via SWA to an old metal clad isolator (FCU?) similar to this:

Which then feeds out to a couple of lights and a double socket.
The plan is to fit a Garage Consumer unit in place of the old switch to service the existing lighting circuit and a radial mains circuit. The mains circuit won't have any kinds of crazy loads (Chest Freezer and occasional power tool usage/18v battery charging).
In regard to populating the consumer unit, will the standard RCD and a 6A/16A MCB setup be appropriate for this? Will an RCD be necessary, considering the supply is coming off an RCBO?
Am I completely mental for considering doing this myself?

Ta.

 

[winston1]

Definitely no need for a RCD. May not even need a garage CU. Radial mains circuit needs a 20 MCB (could be the RCBO in the house if 20 amp). Garage lighting circuit on a FCU with 5 amp fuse.

 

[oldbutnotdead]

How far from the house is the garage and what size is the SWA? As above, no need for local RCD, no real need for garage CU.

 

[SUNRAY]

How far from the house is the garage and what size is the SWA? As above, no need for local RCD, no real need for garage CU.

However I would suggest a local isolator of some description should be in place (although not explicitly required) for future 'maintenance', especially if it's a long walk to the RCBO.

What size is the RCBO and the existing feed cable from it to the garage?

 

[Coliander]

How far from the house is the garage and what size is the SWA? As above, no need for local RCD, no real need for garage CU.

I haven't measured it, but from memory I'd estimate that it's most likely 4.0 - possibly 2.5mm. The SWA terminates into 2.5mm T&E under the bedroom floor which has its external wall directly across from the garage. Again an estimate, but the garage is approximately 5M from the outside of the property and no more than 10M from the main CU.

 

[Coliander]

However I would suggest a local isolator of some description should be in place (although not explicitly required) for future 'maintenance', especially if it's a long walk to the RCBO.

What size is the RCBO and the existing feed cable from it to the garage?

I'd definitely be fixing an isolator of some sort at the very least. Unsure on the RCBO size (at work currently) but I assume 20A would be sufficient? The feed is 2.5mm at its narrowest (CU to SWA termination).

 

[oldbutnotdead]

If it's a 20A RCBO at the CU you're fine. Local isolator is a good plan, you already have one (can't remember if those are single pole or double pole, if it's a single then put a double in).

 

[Coliander]

If it's a 20A RCBO at the CU you're fine. Local isolator is a good plan, you already have one (can't remember if those are single pole or double pole, if it's a single then put a double in).

Cheers. I'll probably replace it anyway as it's 40+ years old and starting to rust! Will likely just swap it with a rotary.
If I go without the CU, I take it I can just take the FCU for the lighting circuit off the mains radial via a socket/junction box?

 

[SUNRAY]

I'd definitely be fixing an isolator of some sort at the very least. Unsure on the RCBO size (at work currently) but I assume 20A would be sufficient? The feed is 2.5mm at its narrowest (CU to SWA termination).

If it's 2.5mm² minimum right through to the 13A sockets and 20A RCBO then as others have said further fusing/MCB is not really required for the power circuit and in fact a SFCU can be included directly in the radial and used in place of a light switch.
An isolation point is good.

 

[oldbutnotdead]

Cheers. I'll probably replace it anyway as it's 40+ years old and starting to rust! Will likely just swap it with a rotary.
If I go without the CU, I take it I can just take the FCU for the lighting circuit off the mains radial via a socket/junction box?

Yep, that'll do it.

 

[Coliander]

If it's 2.5mm² minimum right through to the 13A sockets and 20A RCBO then as others have said further fusing/MCB is not really required for the power circuit and in fact a SFCU can be used in place of a light switch.
An isolation point is good.

Good idea re: SFCU as a switch. Fingers crossed the sparky put in a 20a RCBO for that circuit. Will be cheap enough to have him swap it out if not, though!

Cheers.

 

[markyd1]

So who is going to test and certify the work

 

[Coliander]

So who is going to test and certify the work

The cat.