# Specific cable for three phase (indoors)



## gmgmgm (3 Sep 2018)

I have 3ph at my workshop, and the first 3ph machine coming soon to make use of it.

The machine (Startrite) needs 3 live cables plus earth, though I'd like to wire in neutral now for the future. It will be wired to 4-pin 16A commando sockets.

2.5mm csa is sufficient (run is about 10m). I've looked for suitable cables on Screwfix, but the only multi-core cable is armoured SWA, which feels excessive for indoors.

Is there a suitable multi-core cable available, or does everyone just use multiple sets of 2.5mm twin+earth? I've seen some twin brown cables + earth but I don't know if this is acceptable.

Any links to suitable cables would be appreciated.


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## Sideways (3 Sep 2018)

Take a look at SY cable. It's multicore with a steel woven braid. This provides some extra protection compared to simple pvc, but much more flexible than SWA. It is widely used in practice for connections to motors and aircon outdoor units where there is vibration and a need for some flexibility. I like it for connections between VFD's and motors as an alternative to singles inside flex conduit. If you are using it with CE style plugs, choose 3 core + earth for a delta wired motor or 4 core + earth as you want a neutral available for the future - so the braid can be cut off and used only for protection. There are special glands suited to SY cable when it's installed without plugs that help in terminating and earthing the braid. 
SY is NOT equivalent to SWA in terms of physical protection. Think of it as a robust flex.


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## sunnybob (3 Sep 2018)

This is a star or delta question.
One uses three lives and no neutral. the other uses three lives AND a neutral.
Both should have a ground / earth wire from the body of the machine to the earth of the system.

The plug will be either a 5 or 4 pin commando type.
You need to be very clear which way your machine is wired, because they aint interchangeable.


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## flh801978 (3 Sep 2018)

Bob its nothing to do with star or delta
sometimes machines need a neutral for control gear or for single phase accesories
I would wire in with 4 or 5 core swa to a 4p + e commando socket 16 amp
if your machine is a 3 phase only just use the 3 lives
if you need a neutral for a machine in the future then you will have the neutral allready there for use
It goes without saying that you should use the earth terminal
use 4 core swa if you are happy with using the stranded outers as earth or 5 core if you would rather have a dedicated conductor for earth.
I usually use the extra conductor unless the customer is exceedingly tight


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## sunnybob (3 Sep 2018)

I'm 10 years out of date now, but i used to install 3 phase machinery and it had to have a braided outer sheath connected at one end to the earth circuit with clear plastic over the braid.

Mind, it was 4 mm 5 core cable, which might be a tad excessive for a table saw. :roll: :roll:


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## Sideways (3 Sep 2018)

sunnybob":1n7l37jt said:


> I'm 10 years out of date now, but i used to install 3 phase machinery and it had to have a braided outer sheath connected at one end to the earth circuit with clear plastic over the braid.
> 
> Mind, it was 4 mm 5 core cable, which might be a tad excessive for a table saw. :roll: :roll:



There is not and has not been a requirement like that in UK IET wiring regulations within the last > 10 years Bob. You may well have been working to a factory standard however. Clear sheath over braid is typical of SY cable. Earthed at one end only would suggest an attempt to use the screen to reduce electromagnetic interference emitted by the cable - especially if the motor was being fed from a VFD - they create high frequency electrical noise that normal mains does not.

For clarity - I read the OP to be asking about how to connect his new machine to an existing fixed installation. Assume the fixed wiring, circuit breakers and sockets all to be in place.
If an extension to the fixed installation is needed and you have to ask for advice online, you should be getting a sparky to do it. The installation has to comply with the wiring regs (colours, cable size calculations, installation methods and testing ...) whoever does it. In a home workshop new circuits are notifiable work under building regs. In a commercial workshop, you have HSAW, EAW, Duties of Care and more to think about. Best to get someone qualified to do it.


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## gmgmgm (4 Sep 2018)

Thanks all. This is actually to extend the fixed installation (about 12m, to a new socket on the wall). The machine will then plug into the socket with its own wire.

The machine uses 3p+e (4 wires), so no need for Neutral. But it seems that 5-pin connectors are standard so I may as well put in the neutral wire now.

Seems like consensus is to put in a single multi-core cable (like SY / SWA) from the Consumer Unit to the socket on the wall instead of separate cables. (The machine already has its own flexible wire which looks like SY).

5-core SY cable: £23 for 10m from Toolstation: https://www.toolstation.com/shop/Electr ... ble/p88779

Annoyingly I need about 12m. Screwfix doesn't seem to sell SY cable. Other vendors have a few options, so I'll keep looking. 4-core cable is clearly easier to find than 5-core, and I'd prefer to have five clearly-coloured cores to adhere to the colour regs.


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## mbartlett99 (4 Sep 2018)

RS Components will sell the cable you need - whether its at a reasonable price is another thing.


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## Normancb (4 Sep 2018)

Try your local branch of TLC Electrical. They do 5 core 2.5mm by the metre in both PVC and SY sheath


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## Sideways (4 Sep 2018)

Hi. As it's extending the fixed installation, even though you think it's overkill indoors, I recommend that you use either SWA or the other standard method is single stranded conductors inside conduit. A length of SWA and a couple of glands will probably be cheaper than buying four or five reels of single core in the 3 phase colours. I wouldn't use SY for fixed wiring. 
And don't forget that the size of wire is dictated by the circuit breaker that's protecting the wiring, not the load that you intend to connect. So if you're decided to do the work yourself, use a cable size that is at least the same conductor areas as the wiring that you are extending.
Cheers


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## Myfordman (4 Sep 2018)

you need 3185Y in the correct current rating for the job.


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## n0legs (4 Sep 2018)

SWA the same size as already installed, to extend the fixed wiring.
Correctly terminated in the appropriate glands please.
Running a neutral with all 3 phase is a good idea and costs little.
The steel wire armour may be used as the CPC/"earth" depending upon size of conductor. In most occasions it will be adequate. My, and many other engineers, preference is for a 5 core cable to be used (3ph, N and E). This is due to seeing many poorly terminated armoured cables. 
SY cable is not favoured for fixed low voltage wiring, I'm pretty sure this is in BS 7671.
If the SY cable is used, the outer braid should be earthed. If the clear outer sheath is breached, the braid becomes/is an exposed conductive part. As is a metal gas pipe and metal water pipes. 
A side note,
As an apprentice I was taught that by taking to the extreme the issue of crossbonding, even Crittall steel window frames could/should be bonded. 
Why??
Husband decides to hoover the car out. Throws the cable through the window and plugs in. Wife decides window is open too wide. Think about it.


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## Sideways (4 Sep 2018)

3185Y
:-(


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## gmgmgm (5 Sep 2018)

Thanks everyone for your help.

Myfordman, I don't think 3185Y is suited - it's an unprotected flex, but thanks.
SY isn't suited for fixed installations, so SWA (or single wires in conduit) is the preferred approach. There is dissension in the electrical community (see IET) about whether SY meets BS7671 for wall<>machine flex, but that's a separate issue, and it's certainly commonly used for the purpose.

I've bought the SWA, along with the suitable glands and clamps. 5-core "6945x" was indeed hard to find (TLC have stopped stocking it), so have ended up with 4-core "6944x" , using the cover/CPC as earth. Not as ideal as 5-core, but I understand it meets the regs. I need neutral in case I pull a single phase supply off in the future.

For anyone else looking for suitable 4-core cable, TLC & Screwfix has good stock. Toolstation are temporarily out of stock. Best site I found was Edwardes Bros, where it's easy to select the right size clamps and glands to go with the wire. And they have a fitting video online. There's also a good guide at http://wiki.diyfaq.org.uk/index.php/Terminating_SWA but be aware of competency!


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