"Get an electrician" - Wiring Questions :) CU, Outdoor Cable, etc.

[dlockers]

Hi folks,

Just looking for some guidance on how deep I need to dig in my pockets - diagram below:

The problem statement is: I need to hook-up the garden room to power; for lights, sockets (laptop/tv/monitor/usual home office stuff) and potentially a split AC unit.

I think the most correct answer is to run a new armoured cable from Garden Room to CU, however I really want to avoid this for a while. I would mean quite a bit of upheaval as it means emptying the log store, digging up the side return (which is pure concrete) etc etc. I need to fix the side return in general but don't want to tie all the jobs together if I can avoid it.

It seems the current setup has worked perfectly for 2 decades or so, so presumably it was correct at some point. I had an EICR done as part of my house CU change, and he did test the sockets at the far end of the armour cable (it used to terminate in the old shed).

I suppose therefore my question is whether I can take the armour that comes out the back of the workshop and stick it into a mini CU to drive some lights/sockets - and possibly a split AC unit in the fullness of time.

There is no load on the workshop typically, other than an Alexa/cameras/PoE switch.

Thanks!

 

[Oh Ed not again.]

How long is the run from the CU to the workshop? I'd be looking at armoured cable back to a consumer in the workshop where you can properly distribute to the loads you need in the workshop and garden room.

A/C, power tools etc. can have quite a draw and I think 13amps is aiming a bit low.

 

[dlockers]

How long is the run from the CU to the workshop? I'd be looking at armoured cable back to a consumer in the workshop where you can properly distribute to the loads you need in the workshop and garden room.

A/C, power tools etc. can have quite a draw and I think 13amps is aiming a bit low.

The actual SWA is about ~2m. Distance to the CU from there-on is ~8m. Total ~10m.

Are you thinking upgrade/remove the 13amp fuse spur (it is chased into the wall but I am sure it is possible) and then terminate the SWA into a mini CU in the workshop? That sounds plausible, just not sure how much cable I have to play with. Good thought!

 

[Oh Ed not again.]

I think the correct way to do this is a separate breaker in the main CU feeding the garage, armoured cable to a smaller CU in the workshop.

Then from the work shop RCBOs to protect your circuits. You could probably get away with radials for ease, provided you use the correct rated cabling for the load. Quick read suggests 2.5mm for 20A and 4mm for 30A.

However, IANAE. I'm pretty sure there's a couple of here who will be along soon

 

[Richie]

I'm no electrician but I would do it the way suggested - essentially keeping the "home" electrics separate from the "outside" electrics

Extra benefit is, if you happen to trip the electrics when you do something you're not meant to (), at least it wont trip the house and give you an angry wife to also deal with

 

[Simon42]

What are the conductor sizes in the existing SWA as that external size could be 1.5mm or 2.5mm?

The current capabilities of SWA are higher than standard T&E and I would be looking at 32Amp+ to the shed to supply its mini CU and then onto the summer house (which would mean a larger internal cable from the house CU). The A/C size has a big impact on this (and the distance to it) as the larger units will need more when starting and you need to allow enough for larger tools as mentioned. You don't want to be tripping out a breaker on peak loads.

 

[dlockers]

I think the correct way to do this is a separate breaker in the main CU feeding the garage, armoured cable to a smaller CU in the workshop.

Then from the work shop RCBOs to protect your circuits. You could probably get away with radials for ease, provided you use the correct rated cabling for the load. Quick read suggests 2.5mm for 20A and 4mm for 30A.

However, IANAE. I'm pretty sure there's a couple of here who will be along soon

I think you're right - the annoying thing is the SWA to the workshop is cut quite short/chased into the walls of the utility room, so I am back to digging up the side return.

-------------

Sounds like a heath robinson solution may be the only way in the interim (take the SWA out of the workshop and pass it into the garden room). Doesn't seem like there is a half way solution that is more correct.

I guess I am "safe" as there is a 13amp fuse right at the beginning of the run, so it'll never catch fire etc. It is also into a 16amp RCBO at the CU.

 

[dlockers]

What are the conductor sizes in the existing SWA as that external size could be 1.5mm or 2.5mm?

The current capabilities of SWA are higher than standard T&E and I would be looking at 32Amp+ to the shed to supply its mini CU and then onto the summer house (which would mean a larger internal cable from the house CU). The A/C size has a big impact on this (and the distance to it) as the larger units will need more when starting and you need to allow enough for larger tools as mentioned. You don't want to be tripping out a breaker on peak loads.

I can't tell this second, I will check that out though. Is 12.3mm at the light end? I hear people talking about SWA but I guess they must be referring to wire diameter not external.

 

[Oh Ed not again.]

I think you're right - the annoying thing is the SWA to the workshop is cut quite short/chased into the walls of the utility room, so I am back to digging up the side return.

-------------

Sounds like a heath robinson solution may be the only way in the interim (take the SWA out of the workshop and pass it into the garden room). Doesn't seem like there is a half way solution that is more correct.

I guess I am "safe" as there is a 13amp fuse right at the beginning of the run, so it'll never catch fire etc. It is also into a 16amp RCBO at the CU.

Is the CU on an outside wall? Can you go out the back and route armoured cable to the workshop?

 

[jpaul]

Longer term - are you planning a higher power ev charger for front garden, so main CU may need an update too/soon ?
can you have the Armoured cable above ground in a steel box on edge of property ... had watched this at w/e on back of Motors thread

ZAPPI EV CHARGER installation UK - It WASN'T easy - find out WHY

A home EV charger installation is a trade-off between where you can park an electric car and where the power supply to the property is located.In this projec...

youtu.be

 

[dlockers]

Is the CU on an outside wall? Can you go out the back and route armoured cable to the workshop?

Yeah it is - the "drama" I have is digging up the concrete sidereturn to bury it (and the rules that go along with that lol). Basically I am fully committed to doing it properly, but I am just not sure I have budget/time to do it properly RIGHT now.

Seems consensus is the 2.5 T&E to the spur probably not great, and then the SWA may be undersized, and actually I need a CU in the workshop anyways. There isn't any half way half of me achieving any of that I don't think - it just needs to be properly at the right point.

Longer term - are you planning a higher power ev charger for front garden, so main CU may need an update too/soon ?
can you have the Armoured cable above ground in a steel box on edge of property ... had watched this at w/e on back of Motors thread

ZAPPI EV CHARGER installation UK - It WASN'T easy - find out WHY

A home EV charger installation is a trade-off between where you can park an electric car and where the power supply to the property is located.In this projec...

youtu.be

Main CU has already been upgraded/made ready for an EV. I have a dedicated 2.5 T&E to an outdoor 13amp at the moment.

 

[jpaul]

Main CU has already been upgraded/made ready for an EV.

hadn't realised you had consciously chosen granny versus 7kw future proofish
that vid shows news install with rcbo on every circuit , surge protection, & armoured car, all in one cu.

 

[b0rn2sk8]

@dlockers I know you like a good temporary solution, so how about going overhead to the workshop until a point that you can bury the cable?

If you leave enough slack in the cable at one end, you’ll not need to call anyone back to rework the cable when you [eventually] bury it to finish the job

6mm out to the workshop will give you 40A, you can then run another 6mm out to the garden room from the workshop sub board. That will give you 40A across the two buildings but also the ability to draw the full 40A in each location. That should be plenty.

You’d need to run a catenary wire to attach the cable to but you can take it down later.

 

[Richie]

@dlockers I know you like a good temporary solution, so how about going overhead to the workshop until a point that you can bury the cable?

If you leave enough slack in the cable at one end, you’ll not need to call anyone back to rework the cable when you [eventually] bury it to finish the job

6mm out to the workshop will give you 40A, you can then run another 6mm out to the garden room from the workshop sub board. That will give you 40A across the two buildings but also the ability to draw the full 40A in each location. That should be plenty.

You’d need to run a catenary wire to attach the cable to but you can take it down later.

You do realise that, to @dlockers, temporary tends to mean permanent... The words are interchangeable

 

[b0rn2sk8]

You do realise that, to @dlockers, temporary tends to mean permanent... The words are interchangeable

I know, that’s why I said he would need to run a catenary wire rather than just lashing it in

 

[dlockers]

hadn't realised you had consciously chosen granny versus 7kw future proofish
that vid shows news install with rcbo on every circuit , surge protection, & armoured car, all in one cu.

Yeah there was no way I'd spank a grand on a charger for our use case - just didn't make sense. Granny charge over night at 8.5p; it never gets lower than ~20% and its always in the healthy slow charge/never above 80% range.

@dlockers I know you like a good temporary solution, so how about going overhead to the workshop until a point that you can bury the cable?

If you leave enough slack in the cable at one end, you’ll not need to call anyone back to rework the cable when you [eventually] bury it to finish the job

6mm out to the workshop will give you 40A, you can then run another 6mm out to the garden room from the workshop sub board. That will give you 40A across the two buildings but also the ability to draw the full 40A in each location. That should be plenty.

You’d need to run a catenary wire to attach the cable to but you can take it down later.

Ah yes I do have some leftover pipe from the drain fix

I had considered overheard but it feels way too bodge, even for a temporarily dlockers job. I also don't need 40amp in each location - not in any pressing kind of way.

Sounds like the "half way" job is as much effort as just digging the concrete up and doing it properly. The problem is I expect a sparks will want silly money...........Hmmm.

Maybe I pause the "proper" job as I intend to whack solar on the workshop at some point, and I'll probably need more than a basic CU to make that happen.

You do realise that, to @dlockers, temporary tends to mean permanent... The words are interchangeable

 

[Syla5]

Personally i would take armoured out the back of your CU in the house and to the workshop where it feeds a new CU, which you can then run circuits off of, 2 for the workshop (lights and sockets), 1 additional armoured out to the Garden room with its own CU for lights and sockets. That way you have a failure in the Garden room you know were it is, workshop the same, and in both cases they are separate from the main house as well.

Plus if your house main CU is up against the exterior wall then its a very easy solution to go straight out the back with the armoured. You dont even need to trench it until you get to the end of the house to where you need to run it from house to workshop.

 

[b0rn2sk8]

That’s what I was trying to suggest but put more eloquently.

If you don’t want to trench it in yet or go overhead, perhaps a cable protector is more up your street as a temporary measure e.g.

https://www.screwfix.com/p/coba-europe-cablepro-gp1-medium-duty-cable-cover-3m-black-yellow/

If you didn’t go 6mm, you’d probably need to go 4mm @ 32A. 2.5mm @ 16A/20A doesn’t give you much headroom to run AC and loads.

You also need to consider voltage drop of the run.

 

[radderfire]

Apart from the AC, another option might be a portable power station, which can also recharge using solar:

Jackery Portable Power Station for Camping and Home | Jackery UK

Buy the new Jackery Solar Generators, Portable Power Stations and Solar Panels, Shop now with fast&free shipping and enjoy the exclusive extension warranty.

uk.jackery.com

 

[dlockers]

Personally i would take armoured out the back of your CU in the house and to the workshop where it feeds a new CU, which you can then run circuits off of, 2 for the workshop (lights and sockets), 1 additional armoured out to the Garden room with its own CU for lights and sockets. That way you have a failure in the Garden room you know were it is, workshop the same, and in both cases they are separate from the main house as well.

Plus if your house main CU is up against the exterior wall then its a very easy solution to go straight out the back with the armoured. You dont even need to trench it until you get to the end of the house to where you need to run it from house to workshop.

100% this is the correct way, I agree. I am trying to discover an interim method that is 1) worth the effort, 2) at least on bearing for "end state".

I am definitely touching the garden room end imminently, so maybe that's how I start - I can quite easily run a brand new SWA from Garden Room into Workshop, and get that all tidy and ready for a new SWA into the workshop when I get to it.

In diagram form:

So phase 1 -
* New SWA from new CU into workshop.
Question - I guess I don't need SWA inside of the workshop, so I could revert to something else. I have no idea how much SWA is, am I saving anything doing it this way?

Then phase 2 when I dig up the side return, I can run a new feed of armour into the workshop.

Phase 1 no worse than what I have now but future proofs the garden room end and means I never have to touch it again. This feels like progress vs. my other plan!