Wiring for garden office - can I spur off an external socket?

[thatsimpsongirl]

Hi,

I’m not an electrician so seeking advice as to whether my requests were actions correctly or if I need to arrange for additional / remedial work to be done.

During the first fix of a renovation I told the electricians working on my project that I planned to put an office / studio in the garden at a later date & could they run something outside that would be suitable. They told me that they’d install an external socket and that any connection could be spurred off that for an office constructed at a later date.

I am now in the process of getting quotes for the studio and not sure if the external socket will be enough? The renovation isn’t quite finished so although it would be a real pain to run another cable from the fuse box it would be easier to do it now rather than later.

I attach pictures of the cables that are running to the outside as well as the external socket (this one OA036AG) . We would be planning to have a couple of 230v sockets (charging laptops etc) and some lights.

Would be grateful for any advice,

Nikki

 

[pc1966]

It depends very much on what you want to have in the office.

A feed off that socket is likely to be limited to 13A so OK for powering a decent amount of LED lights, a PC or laptop, and a single 2kW heater (not full 3kW). So quite small and limited, but if that is all you plan on doing there it is fine.

If you want a lot more (hot tub, several heaters, etc) it is going to need a dedicated feed and a lot more design information for sizing that.

 

[brianmoooore]

Whether or not you can spur off of that socket depends on what the existing wiring an circuit arrangements are to the socket.
If it is an unfused spur off of a ring final circuit, which is what most external sockets would be, you cannot extend to your studio, unless you install the fused spur BEFORE this existing socket.
Looking at the size and quality of the building you are constructing, I feel it would be a mistake not to install a decent size feed (min 10mm2) direct from your electricity meter.

 

[thatsimpsongirl]

Thanks a lot for taking the time to reply, much appreciated.

I plan to have 4/5 double sockets, some led spotlights, 2 x wall lights and a heater.

I’m afraid I really don’t know if it’s a fused spur from a final ring circuit - the whole place was all re-wired and this external socket was done at the same time as that...

In any case it sounds as if I am likely to need more power than that provided by spurring off the external socket - but I will obviously ask a specialist to come and assess things.

Thanks again,

Nikki

 

[westward10]

I don't understand if you flagged this up when the first fix was being done why they didn't include putting in a dedicated supply.

 

[Pete999]

Hi,

I’m not an electrician so seeking advice as to whether my requests were actions correctly or if I need to arrange for additional / remedial work to be done.

During the first fix of a renovation I told the electricians working on my project that I planned to put an office / studio in the garden at a later date & could they run something outside that would be suitable. They told me that they’d install an external socket and that any connection could be spurred off that for an office constructed at a later date.

I am now in the process of getting quotes for the studio and not sure if the external socket will be enough? The renovation isn’t quite finished so although it would be a real pain to run another cable from the fuse box it would be easier to do it now rather than later.

I attach pictures of the cables that are running to the outside as well as the external socket (this one OA036AG) . We would be planning to have a couple of 230v sockets (charging laptops etc) and some lights.

Would be grateful for any advice,

Nikki
View attachment 64886
View attachment 64884

Is the outside socket you want to spur off ofa spur already, or is it part of the RFC??

 

[loz2754]

I thought the same thing as @westward10.
Still it's a bit too late for recriminations I guess...

 

[ipf]

I thought the same thing as @westward10.
Still it's a bit too late for recriminations I guess...

.....even if you were told a load of bunkum by the original spark!!

 

[Pete999]

I thought the same thing as @westward10.
Still it's a bit too late for recriminations I guess...

What did W10 SAY then can't see his response.

 

[thatsimpsongirl]

@Pete999 I'm sorry I'm afraid I don't know. The external socket has its own wire from the fuse box if that means anything?

Yes @loz2754 @westward10 I don't know why they didn't either, I definitely asked for it though, I remember the conversation as I had to ask them to explain what spurring was as it wasn't something I was familiar with.

To be honest it's not really surprising (although doesn't make it less frustrating) as there were quite a few things I asked for that they didn't do / did differently to how I'd asked for them to be done (socket placement etc.). I managed to get the main contractor to get them to change most of it to the way I'd asked but I had no idea that the external socket might not be enough until I started getting quotes for the work outside.

But hopefully I will be able to find a solution (or rather get another electrician who can!).

 

[mattg4321]

That socket having ‘it’s own wire from the fusebox’ is a good sign if true. It all depends what size it is though as to how much power it can take!

 

[brianmoooore]

If there is a breaker in the CU (fusebox) that is labeled outside socket only, and this is true, then you can go on from it to your studio. Not even a fused spur is required, as long as the cable to the studio is of an adequate size for the rating of the breaker.
This would be fine if you were building a small garden shed, but I still say you'll eventually regret it if you don't give this place its own largish dedicated feed.
What is the rating of the breaker? (likely B16, B20 etc.)

 

[Spoon]

The external socket has its own wire from the fuse box if that means anything?

As above, things are looking better if this is true.
As above, see what size breaker it is wired to.

 

[Dustydazzler]

For the sake of a few hundred quid , I would buy some 4mm swa and put in a dedicated 30a supply

you are spending thousands on a nice outbuilding , why skimp now

 

[brianmoooore]

For the sake of a few hundred quid , I would buy some 4mm swa and put in a dedicated 30a supply

you are spending thousands on a nice outbuilding , why skimp now

Costs little more to stick in 10mm2 or 16mm2. I wouldn't bother with 4mm2

 

[Spoon]

For the sake of a few hundred quid , I would buy some 4mm swa and put in a dedicated 30a supply

you are spending thousands on a nice outbuilding , why skimp now

The outside socket might be wired in 4mm... We may find out...

 

[Spoon]

Costs little more to stick in 10mm2 or 16mm2. I wouldn't bother with 4mm2

32A should be enough for a small office.. 4mm should be enough.

 

[brianmoooore]

How about the hot tub/sauna?

 

[Dustydazzler]

i like working with 4mm swa and 30amos is plenty for most domestics

10-16mm is overkill for domestic office power

 

[brianmoooore]

i like working with 4mm swa and 30amos is plenty for most domestics

10-16mm is overkill for domestic office power

There's the cable length to consider as well.

 

[thatsimpsongirl]

Thanks to all of you for your replies.
I’ve attached a photo of the fuse box & the cables coming out of it...Not totally sure what I’m looking for?!

 

[brianmoooore]

B32 looks promising!

 

[Spoon]

Outside socket is on a 32A breaker

Bugger, @brianmoooore beat me to it.

 

[Dustydazzler]

You might be in luck of the outside socket is in 4mm cable you could piggy back off this

 

[thatsimpsongirl]

How about the hot tub/sauna?

? that's for the next reno

 

[brianmoooore]

You might be in luck of the outside socket is in 4mm cable you could piggy back off this

With no fused spur required

 

[thatsimpsongirl]

You might be in luck of the outside socket is in 4mm cable you could piggy back off this

Thanks. How would I find this out?! Here are the cables before the kitchen units were put in - it’s one of these...you can see the hole in the wall to the outside. I’m not sure if this is what you’re asking me though!

 

[Spoon]

I'm not sure what I'm seeing in that picture. It looks like coils of cables with about 4 cables going into the wall from the coil.
Is the outside socket behind the coils?

 

[brianmoooore]

If the outside socket is sized according to the regs., then it is a minimum of 4mm2.

 

[thatsimpsongirl]

I'm not sure what I'm seeing in that picture. It looks like coils of cables with about 4 cables going into the wall from the coil.
Is the outside socket behind the coils?

Sorry it’s not that clear is it! The outside socket is directly behind the wall with the wires on it - the kitchen is in now (well nearly - as you see) and the induction hob and a socket will be in this island bit, hence all the wires.

 

[loz2754]

What did W10 SAY then can't see his response.

Post number 5 I think Pete.

 

[brianmoooore]

Very roughly, what is the distance from the external socket to the new studio?

 

[thatsimpsongirl]

Very roughly, what is the distance from the external socket to the new studio?

About 5m. So not too far.

 

[brianmoooore]

In that case, a 32A supply to your studio should be possible. Go on from the outside socket with 4.0mm2 or 6.0mm2 3C SWA to a small non RCD consumer unit in your studio.
Only downside, is that the RCD for the studio will be indoors on the main CU, so if it trips you will lose all power to the studio, including lights, and you will have to go indoors to reset it.

 

[Pete999]

In that case, a 32A supply to your studio should be possible. Go on from the outside socket with 4.0mm2 or 6.0mm2 3C SWA to a small non RCD consumer unit in your studio.
Only downside, is that the RCD for the studio will be indoors on the main CU, so if it trips you will lose all power to the studio, including lights, and you will have to go indoors to reset it.

I'm surprised Brian that you would condone changing the size of the cable at the point of connection to the outside socket, not one person has asked if this outside socket is a spur or whether it is part of an RFC, apart from myself post 6, sorry for the disagreement to your reply.

 

[loz2754]

Hi Pete. I believe the OP has stated that the socket is fed directly on its own 32 amp MCB in the consumer unit.

 

[Pete999]

Hi Pete. I believe the OP has stated that the socket is fed directly on its own 32 amp MCB in the consumer unit.

 

[Pete999]

Right thanks for that must have missed that,

 

[brianmoooore]

It's not been verified that the existing outside socket is the only connection to a 32A MCB, wired in 4.0 or 6.0mm2 T&E, but the signs are promising. My last post does depend on this being true, of course.

 

[pc1966]

If, as it appears to be, it has a dedicated 32A MCB feeding it then it should be at least 4mm cable and plenty capable of feeding the garden office. When all of the current work is done the completion certificate should confirm that, along with various other measurements that would allow the correct design of the office electrics.

The only possible issue is what @brianmoooore pointed out - the RCD protection is in the house's main CU (fuse box) and shared with other circuits. Not normally a problem, but an extra inconvenience if a fault does develop (compared to separate RCD).

For sockets and lights in a small office style arrangement you almost don't need a 2nd CU in the out building as the lights could come off a FCU (fused connection unit), but for all the cost of a CU it provides a handy place to isolate and test circuits, even if the MCBs in it have little selectivity with the feed from the house.

 

[thatsimpsongirl]

Thanks @pc1966 and @brianmoooore - and thanks in general to everyone for all the replies, I didn't expect to receive so much good advice in such a short space of time!

I note your points re the cable size / whether there are any other connections to the 32A MCB / RCD protection (annoying but not insurmountable). The completion cert is not yet done as there are a few things still to be connected up (kitchen appliances etc.) but will show this to whoever does the work outside once I receive it.

Obviously I will be getting a qualified professional for all the studio electrics but it does seem to make a difference in how seriously I am taken on site if I'm well informed (at least as far as I can be as a non-specialist). Just wish one of you guys had been my electricians in the first place!

Thanks again

Nikki ?