2.5mm SWA as garage lighting

[FooManChu]

Hi

I've scanned through some of the previous posts and noted when people wish to run armoured cable to sheds. Noted the 10mm recommended thickness as well that seems to be mentioned in most instances.

I have about 5 double sockets, all weatherproof linked with SWA underground cabling running throughout my garden, all tested by a spark and certificate provided. The intention is to use these sockets merely to plug in lighting and such that I don't have to bother getting a spark to connect fixed lighting connections each time.
I also would like to light a few garden sheds using the same sockets by running 2.5 mm swa underground from one socket (via a three pin plug) to a shed and simply having those sheds lit by way of an extension from one of the sockets. All sockets are on a 15amp (I think) circuit.

My question is would 2.5mm 3 core SWA be sufficient for this purpose? I've seen smaller armoured cable but I'd like to run it underground as opposed to surface.

 

[Taylortwocities]

Swa is not suitable for connecting to a 13A 3-pin plug.

 

[FooManChu]

ok thanks. So what would your suggestion be?

 

[SimonH2]

Connect the SWA into one of the existing sockets, using the correct gland for outdoor use.
In the shed, connect the other end into another socket and add a switched & fused spur (FCU, Fused Connection Unit) which can act as the switch for the lights as well as proving the fusing required. Repeat for each shed.
In principle, as this is a radial circuit, you can tee off it at any point (ie another shed or socket as most convenient. However, you need to be aware of how adding extra length to the cable make affect protection - there is a maximum resistance allowed to ensure that any fault current is sufficient to trip the fuse/circuit breaker in a timely manner - and so you may be restricted in how far you can extend the length of the circuit. There are also volt drop considerations.
However, in terms of protection, it is the distance (as the cable runs) to the furthest point that matters; not the total length of all the cable used. So tee'ing off a socket close to the house is unlikely to be an issue, but extending the end of the circuit from the furthest socket might be.

 

[Notch7]

Connect the SWA into one of the existing sockets, using the correct gland for outdoor use

I dont know if thats notifiable or not, but if you are doing it yourself bear in mind terminating SWA is awkward without the correct tools. Ive used a plumbers pipe cutter to score the steel armour wires -Im sure pro electricians would cringe but its worked for me.

 

[FooManChu]

Thanks SimonH2. Would connecting to a socket via a gland be classed as Part P notifiable. I rather think it would be as its classed as a permanent connection. I take your point on the farthest length of cable and will look at the relevant tables to check for the voltage drop. One socket at the moment is fastened to one shed already but I intend to move that shed around 30 feet away. I have another socket closer but not as convenient to run cable from. I don't suppose running a cable to a shed with its own trip switch would be a good thing to do would it?

So what is the smallest armoured cable I could use in a 13amp plug? 1.5mm perhaps?

 

[FooManChu]

Thanks Notch7.

 

[FooManChu]

Incidentally I've seen this kind of thing used before. Its not the sort of cable to bury but it has some armour protection.

http://www.batt.co.uk/products/view/773/VO-YMvKasmb-flame-retardant-braided-power-cable

I could run that from one socket which is close to a fence and then run it along the fence to the shed.

Or.....could I run a small piece from a socket to a junction box and run SWA from a gland from that junction box? Technically the entire extension would be temporary and outside of Part P.

 

[SimonH2]

I dont know if thats notifiable or not, but if you are doing it yourself bear in mind terminating SWA is awkward without the correct tools. Ive used a plumbers pipe cutter to score the steel armour wires -Im sure pro electricians would cringe but its worked for me.

Actually it's not far off the method I was taught - substitute hacksaw for pipe cutter and it's the same process. The trick is to only score (or perhaps go half way through) the wires all the way round, then flex them till they break off. If you cut all the way through then it's very easy to go too far - as I've seen on a "professional" install of an aircon unit at work. It had been working fine for several years, then started tripping the supply breaker. One of the outside sparkies we use tipped me off on what to look for, and sure enough there were tell-tale scorch marks behind the cable where the installer had damaged the insulation and in damp weather it was arcing across to the metalwork

Would connecting to a socket via a gland be classed as Part P notifiable. I rather think it would be as its classed as a permanent connection.

Permanent has nothing to do with it (since 2013 when the building regs were changed again). There is not, and never has been, any such thing as "Part P notifiable" "Part P" refers to Part P of the building regs which is just one paragraph that essentially says electrical work must be safe - nothing more. What's more, the requirement in Part P to do electrical work safely applies whether or not the work is notifiable.
The Building regs of 2005 introduced a complicated list (in Schedule 4) of things that were and weren't notifiable - but that's nothing to do with "Part P". One of the things that was not notifiable was a system using factory made assemblies that just plug together - so very quickly vendors came out with various plug together systems that were (for some of them) as near to being the same as a permanent installation while obeying the letter of the regs. Of course, some of the vendors were not at all shy at pushing a sometimes misleading interpretation of the regs in order to persuade the general public to part with their cash.
It was seemingly recognised by TPTB that the 2005 regs were too restrictive and this was having too many negative effects, so in 2013 they were relaxed significantly. Now (in England, other parts of the UK vary) there are only three things that are notifiable :

• Work within the zones of a bathroom
• Replacement of a consumer unit
• Addition of a circuit

And that's it Adding sockets to your existing circuit is not notifiable - but it must be done safely (Part P applies to ALL electrical work in domestic properties).

So what is the smallest armoured cable I could use in a 13amp plug? 1.5mm perhaps?

SWA is not suitable to terminate into a 13A plug. You would have to strip back the pouter sheath and armouring to get down to a round 3 core cable. But then you'd have no way of connecting the armour to anything. To solve that latter issue you'd need to fit a gland on the end of the armouring and an earth tail - which you'd struggle to fit into the plug alongside the 3 core cable (to meet regs, this separate earth would need to be 4mm²).

 

[SimonH2]

Pedant mode on ...
If you strip back the armour, then what you have left is a rather stiff 3 core sheathed flex. If you don't accept that argument, then I can lay claim to have terminated SWA network cable into "RJ45" plugs

 

[FooManChu]

Right ok. So forget SWA into a 3 pin plug. Silly idea and I'll accept any further recommendations as to possible alternatives. If glanding it via the socket is feasible then will 2.5mm SWA be sufficient or are there alternatives via a 3 pin plug.

Thanks

 

[Risteard]

If you strip back the armour, then what you have left is a rather stiff 3 core sheathed flex.

It isn't a flex in any sense.

 

[bernardgreen]

Re that cable

Applications: power cable for use in industrial applications, Suitable for underground laying

but it does not come with a green / yellow conductor for the Earth. Using the braid as the only Earth runs the risk of the braid being corroded away and thus no Earth to the installation supplied by the cable. This can happen if there is any damage to the outer sheath that allows moisture to get into the braid,

 

[Harry Bloomfield]

I dont know if thats notifiable or not, but if you are doing it yourself bear in mind terminating SWA is awkward without the correct tools. Ive used a plumbers pipe cutter to score the steel armour wires -Im sure pro electricians would cringe but its worked for me.

A full size hacksaw works on the larger SWA and a junior works on the smaller cables. It is how the professionals do it and it works fine. The idea is to just nick the steel armour, just enough to weaken them so they can be bent back and forth to break them. The only special tool is like a G clamp, with a blade, but few bother with one. - Says he who has made off thousands of SWA ranging from the smallest to the largest available.

 

[SimonH2]

It isn't a flex in any sense.

No, it's not a "flex" like you'd have on something like a domestic iron - but it is a flexible cable which would be suitable for the limited amount of movement that a permanently plugged in and non (or limited) movement item would have. Context is everything - which is why I said it would be a "rather stiff" flexible cable. It would also be quite difficult, but not impossible, to terminate into a 13A plug.
In any case, it's not a method I'd recommend, especially as the OP has (I assume, we don't know the size and type of sockets) the option of glanding the cable directly into one of the existing sockets (or adding a suitable JB).