Garage circuit question

[Peter Johnson]

When I first bought this house, nearly 30 years ago, I installed a
socket near the garage doors, wired back to the then existing fuse
box.
Then when two sockets were needed to power the roller shutter garage
doors I wired them back to a junction box placed in the socket
circuit. Subsequently I installed an external grade socket, with a
switch fused spur, at the rear of the original socket.
When the fusebox was upgraded a few years ago the circuit got its own
mcb.
Given that the cirecuit is, in relative terms, rarely loaded, and only
lightly loaded at that, should it be upgraded to be a ring main?
Opinions/advice appreciated. It the answer is yes I'll have it done.
Won't diy.

[Andy Burns]

Post by Peter Johnson
Given that the cirecuit is, in relative terms, rarely loaded, and only
lightly loaded at that, should it be upgraded to be a ring main?

Doesn't sound like there's any need for that, what is it a 16A or 20A
radial, using 2.5mm^2 cable?

[Peter Johnson]

Post by Andy Burns

Post by Peter Johnson
Given that the cirecuit is, in relative terms, rarely loaded, and only
lightly loaded at that, should it be upgraded to be a ring main?

Doesn't sound like there's any need for that, what is it a 16A or 20A
radial, using 2.5mm^2 cable?

30a

[Andy Burns]

what is it a 16A or 20A radial, using 2.5mm^2 cable?

30a

That's not right then, it would need to be 4mm^2 cable for a 30A radial,
if it's 2.5mm^2 you ought to drop it to a 20A MCB/RCBO.

[John Rumm]

Post by Andy Burns

what is it a 16A or 20A radial, using 2.5mm^2 cable?

30a

That's not right then, it would need to be 4mm^2 cable for a 30A radial,
if it's 2.5mm^2 you ought to drop it to a 20A MCB/RCBO.

The devil is in the detail...

Say the original circuit was a 30A fused ring circuit feeding sockets
elsewhere in the house. The addition of a spur in 2.5mm^2 cable to feed
a garage socket would be fine. (Even if the connection point of the spur
was at the fuse in the CU rather than at an accessory / JB on the circuit).

However, when that original garage socket was augmented with an
additional one for the roller shutter, that technically became a spur
feeding a spur. (probably not an actual risk in the grand scheme of
things - however to be properly compliant the split to feed both sockets
could have been done with a fused connection unit to turn the pair of
sockets into a fused spur, or the single socket could have been replaced
with a double since one double socket is permitted on an unfused spur)
--
Cheers,

John.

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[Andy Burns]

Post by John Rumm
The devil is in the detail...
Say the original circuit was a 30A fused ring circuit feeding sockets
elsewhere in the house. The addition of a spur in 2.5mm^2 cable to feed
a garage socket would be fine.

I can't remember now, but I think we've been told the garage has now
become its own circuit?

[Chris Green]

Post by Andy Burns

Post by Peter Johnson
Given that the cirecuit is, in relative terms, rarely loaded, and only
lightly loaded at that, should it be upgraded to be a ring main?

Doesn't sound like there's any need for that, what is it a 16A or 20A
radial, using 2.5mm^2 cable?

30a

If it has a 30 amp MCB then it should be wired with 4sqmm cable, I
doubt if it is. Change the MCB to a 16A or 20A one.

[Chris Green]

Post by Peter Johnson
When I first bought this house, nearly 30 years ago, I installed a
socket near the garage doors, wired back to the then existing fuse
box.
Then when two sockets were needed to power the roller shutter garage
doors I wired them back to a junction box placed in the socket
circuit. Subsequently I installed an external grade socket, with a
switch fused spur, at the rear of the original socket.
When the fusebox was upgraded a few years ago the circuit got its own
mcb.
Given that the cirecuit is, in relative terms, rarely loaded, and only
lightly loaded at that, should it be upgraded to be a ring main?
Opinions/advice appreciated. It the answer is yes I'll have it done.
Won't diy.

Quite unnecessary. If it's wired with 2.5sqmm cable and is protected
by a 20 amp MCB it's exactly as it should be.

I think radial circuits like this are much more sensible than ring
circuits, easier to test etc.

[Peter Johnson]

Post by Chris Green

Post by Peter Johnson
When I first bought this house, nearly 30 years ago, I installed a
socket near the garage doors, wired back to the then existing fuse
box.
Then when two sockets were needed to power the roller shutter garage
doors I wired them back to a junction box placed in the socket
circuit. Subsequently I installed an external grade socket, with a
switch fused spur, at the rear of the original socket.
When the fusebox was upgraded a few years ago the circuit got its own
mcb.
Given that the cirecuit is, in relative terms, rarely loaded, and only
lightly loaded at that, should it be upgraded to be a ring main?
Opinions/advice appreciated. It the answer is yes I'll have it done.
Won't diy.

Quite unnecessary. If it's wired with 2.5sqmm cable and is protected
by a 20 amp MCB it's exactly as it should be.
I think radial circuits like this are much more sensible than ring
circuits, easier to test etc.

Thanks

[Tricky Dicky]

Post by Peter Johnson
When I first bought this house, nearly 30 years ago, I installed a
socket near the garage doors, wired back to the then existing fuse
box.
Then when two sockets were needed to power the roller shutter garage
doors I wired them back to a junction box placed in the socket
circuit. Subsequently I installed an external grade socket, with a
switch fused spur, at the rear of the original socket.
When the fusebox was upgraded a few years ago the circuit got its own
mcb.
Given that the cirecuit is, in relative terms, rarely loaded, and only
lightly loaded at that, should it be upgraded to be a ring main?
Opinions/advice appreciated. It the answer is yes I'll have it done.
Won't diy.

If that is all you require it is not worth going for a ring. I have a ring
circuit for my garage only because I have multiple sockets in a large
garage/workshop with attached office. I have a freezer and tumble dryer in
the garage and need to charge my plug-in hybrid with A “ Granny” lead plus
the need to plug in various power tools in a number of locations. The
office section has several sockets mainly for office stuff, laptop, printer
and WiFi access point as well a fan heater when required.

[John Rumm]

Post by Peter Johnson
When I first bought this house, nearly 30 years ago, I installed a
socket near the garage doors, wired back to the then existing fuse
box.

Back to the fuse box on a separate circuit, or as a branch (at origin)
from an existing one?

Integral garage, or detached?

Post by Peter Johnson
Then when two sockets were needed to power the roller shutter garage
doors I wired them back to a junction box placed in the socket
circuit. Subsequently I installed an external grade socket, with a
switch fused spur, at the rear of the original socket.
When the fusebox was upgraded a few years ago the circuit got its own
mcb.

Suggesting it was just a part of a normal "house" socket circuit previously?

Post by Peter Johnson
Given that the cirecuit is, in relative terms, rarely loaded, and only
lightly loaded at that, should it be upgraded to be a ring main?

I can see no benefit in doing so - and possibly some reasons that would
recommend against.

Rings are very good at providing socket coverage over a wide area. Well
suited to diverse and varied loads, that are spread out (in terms of
position on the circuit). They are less well suited to high current
fixed loads at single points - especially if the point is near one of
the ends of the socket.

Typically with things like a garage circuit, it is common to wire in a
radial (which you might class as a "sub main" if running externally to
an outbuilding). The MCB at the origin being adequate to protect the
circuit from both fault and overload current. If you need lots of
sockets at the far end, then another CU fed from the submain would be
the way to go since you could then run a ring circuit on that if required.

Post by Peter Johnson
Opinions/advice appreciated. It the answer is yes I'll have it done.
Won't diy.

So long as the exterior socket has RCD protection somewhere, I can't see
any reason to change.
--
Cheers,

John.

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| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

[Peter Johnson]

On Sun, 13 Apr 2025 14:22:54 +0100, John Rumm

Post by John Rumm

Post by Peter Johnson
When I first bought this house, nearly 30 years ago, I installed a
socket near the garage doors, wired back to the then existing fuse
box.

Back to the fuse box on a separate circuit, or as a branch (at origin)
from an existing one?

Separate circuit.

Post by John Rumm
Integral garage, or detached?

Integral.

Post by John Rumm

Post by Peter Johnson
Then when two sockets were needed to power the roller shutter garage
doors I wired them back to a junction box placed in the socket
circuit. Subsequently I installed an external grade socket, with a
switch fused spur, at the rear of the original socket.
When the fusebox was upgraded a few years ago the circuit got its own
mcb.

Suggesting it was just a part of a normal "house" socket circuit previously?

No, it wasn't. It was provided just for a double 13a outlet originally
but probably shared a fuse with one of the house circuits. I don't
remember, it was over 20 years ago.

Post by John Rumm

Post by Peter Johnson
Given that the cirecuit is, in relative terms, rarely loaded, and only
lightly loaded at that, should it be upgraded to be a ring main?

I can see no benefit in doing so - and possibly some reasons that would
recommend against.
Rings are very good at providing socket coverage over a wide area. Well
suited to diverse and varied loads, that are spread out (in terms of
position on the circuit). They are less well suited to high current
fixed loads at single points - especially if the point is near one of
the ends of the socket.
Typically with things like a garage circuit, it is common to wire in a
radial (which you might class as a "sub main" if running externally to
an outbuilding). The MCB at the origin being adequate to protect the
circuit from both fault and overload current. If you need lots of
sockets at the far end, then another CU fed from the submain would be
the way to go since you could then run a ring circuit on that if required.

Post by Peter Johnson
Opinions/advice appreciated. It the answer is yes I'll have it done.
Won't diy.

So long as the exterior socket has RCD protection somewhere, I can't see
any reason to change.

Thanks.

[John Rumm]

Post by Peter Johnson
On Sun, 13 Apr 2025 14:22:54 +0100, John Rumm

Post by John Rumm

Post by Peter Johnson
When I first bought this house, nearly 30 years ago, I installed a
socket near the garage doors, wired back to the then existing fuse
box.

Back to the fuse box on a separate circuit, or as a branch (at origin)
from an existing one?

Separate circuit.

Post by John Rumm
Integral garage, or detached?

Integral.

ok

Post by Peter Johnson

Post by John Rumm
Suggesting it was just a part of a normal "house" socket circuit previously?

No, it wasn't. It was provided just for a double 13a outlet originally
but probably shared a fuse with one of the house circuits. I don't
remember, it was over 20 years ago.

The fuse is what delimits a circuit - if you have 5 fuses, then that is
five circuits typically.

So even if you take a separate single cable right back to the CU, and
then hook it up to the fuse currently supplying the downstairs socket
ring, then that new cable[1] becomes part of the downstairs socket circuit.

[1] Something you can do - it is called a "spur at the origin" - it
would be subject to the same limitations as any other spur though.
--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/