cable core colours for 3 phase motors

I intend to replace the cable on my J&S grinder motors. The existing ones (or certainly the sheathing) is hard enough to crack when bent, probably from oil and ageing.

The colour coding on the existing cables is three browns and a yellow/green earth. (This last one is a true earth, fixed to the casing, not a neutral.) I can't seem to find this spec anywhere and I suspect that's because the regulations have changed. Can anyone advise me what combination I should be installing now please?

Also, my preference is for rubber sheathing for oil resistance and flexibility. Am I being a bit old fashioned ?!

I wouldn't consider rubber to be oil resistant. In fact I'd be surprised if you can still get it. Google will give you the current colour codes

Old-style rubber best avoided even if you can find some. It goes hard, cracks and the insulation falls off. Not good with heat and not really oil resistant. Silicone rubber is OK though.

The colours don't matter much because there's no need to distinguish between phases. When flexible wires are used, one of the conventions is Brown, Brown, Brown. Another is Red, Yellow, Blue.

Non flexible cable usually Red Yellow Blue or Red White Blue.

Dave

The UK harmonised standard is brown, black and grey for phases, blue for neutral and yellow/green for earth.

Andrew

Red Black Blue went out more than 15 years ago. Now it's Brown Black Grey.

Red, Blue, Yellow phase colours went out more than 15 years ago. Now it's Brown Black Grey.

Edited By Dave T on 18/09/2022 15:10:42

red yellow blue went out when we were persuaded to harmonise with the EU, who have a very sketchy standard of electrical safety anyway, still using unshuttered sockets, which we changed in 1947!! Now we are no longer in the EU we should go back, but for the fact that brown grey black are easier for colour blind electricians to recognise. Having said that colour blindness and electrical engineering hardly go together even though my dad was both!

Oh dear. There's no doubt now that I've passed my "Best Before" date...

The current best practice cable for this application would be "SY" 4 core (3 + PE) e.g.

https://www.tlc-direct.co.uk/Products/MF1dot5slash4.html.

The phase colour code is for supplies. Ideally it should not be used on a motor that might be reversed. The SY cable linked to has one Green/Yellow for the Protective Earth (PE) and 3 blacks which have numbers printed on them.

Robert G8RPI.

HOFR cable is not hard to find and is a rubber type cable that is Heat Oil Flame Retardant hence HOFR. I doubt that it is a natural rubber to meet that requirement but it is nicer than PVC cable for power tool flex.

Mike

Only for Low Voltage !! (0 - 1,000 volts) anything higher in the UK is still Red Yellow Blue - thankfully

It was the most by most ill thought through changes that happened in Electrical Engineering it causes all sorts of issues when connecting 'new' to 'old'

Old Harmonised

Red = Brown (L1)

yellow = Black (L2)

Blue = Grey (L3)

Black = Blue (N)

No prizes for spotting where the mistakes can creep in !!!

(Yet another example of the EU imposing a change on the UK that was stupid !!)

Does anyone know the reasoning behind the 3 blacks for phase power idea. Seems potentially dangerously confusing to me. Especially when done with 3 unidentified single cores pulled through conduit. Back in the day 3 red singles seemed to be common for factory et al installations.

My workshop is single core in conduit but its all brown, black, grey connected to the L1, L2 and L3 outputs of the phase converter with blue for neutral. So everything is the same. If any motors ran backwards I changed the internal motor connections, not the supply cables, making sure the control gear followed the same conventions and was laid out as per the wiring diagram in the manual.

I can do without surprises like things starting up backwards if plugged into a different socket for any reason. All my machines connect via 5 way fully populated plugs and socket with a proper lever disconnector immediately upstream of the socket. I may not currently have anything that needs the neutral connector but its there, properly connected and ready to go. Proper connection and safe termination of anything to do with 240 / 440 volts is a religious matter for me!

I use the bright yellow Lewden disconnectors with the big red lever so I can see right across the workshop if something is on or off. Having a plug on the machine lead means that I can simply pull the plug if I really, really want to be sure something is off.

Have absolutely zero desire to verify that getting tangled up in something spun by a 3 hp motor hurts. My imagination will do just fine thanks!

Clive

Edited By Clive Foster on 18/09/2022 16:38:15

I have used SY cables for many power supply connections and are my preferred connection cable especially where there is possibility of movement. There are many sizes of cable with many numbers of cores but all have an extra layer of protection with a braided steel sheaf in the middle which is earthed with the correct cable gland as extra protection and the cable is not affected by oil etc. Every core is numbered its full length and it is easy to attach a rubber or shrink tube sheaf to each core if you wish to code by colour.

David

If you dig into it, SY cable is not certified for power supply. It is for use as a control cable only. If you buy 24 core SY cable, it will have 23 black conductors labelled from 1-23. The numbers are printed about every 4" on the cable so difficult to be confusing.

I think the proper cable to be used for power supply is H0xRN-F, where x is most commonly 5 or 7 (hundred volts).

See, for example:

https://uk.rs-online.com/web/generalDisplay.html?id=ideas-and-advice/sy-cable-guide

SY is popular as a power cable as it is cheap and robust, but technically it is incorrect.

Yes there is a problem wit SY not complying with BS-something or other. Have no fear though it is plenty good enough for power supplies we have been using it up to 100A for our mobile plant at work now for at least 25 years, all in extreme duty situations. It's very robust.

Only just recently have we had an issue with a main contractor insisting we use HO7RN cables instead of SY, and that was only because of an audit.

Most SY cables are appropriately approved. The X cores in black +PE SY cables are not suitable for 230V flexible leads for direct connection to single phase mains, but only because they don't comply with the colour code. You can get 2+PE SY cables that are Brown, Blue & Yellow/Green (and 3 phase colours) and fully compliant.
For connecting between switch gear and a motor the numbered black core + green/yellow is fully compliant. It is also as I stated earlier, incorrect to use the 3 phase colour code between switchgear and motor when the motor is reversable because in at least one direction the colours will be wrong.

https://www.clevelandcable.com/SY-control-flexible-cable-pvc-up-to-95mm/

The use of a single colour in conduit is purely down to cost. It costs more to stock 4 or 5 colours than two or three.

Robert G8RPI.

Edited By Robert Atkinson 2 on 18/09/2022 18:27:51

Thanks chaps for all your input. Your comments have helped me navigate the web more efficiently and now I know hugely more about the subject than I did 4 hours ago. I've also just placed an order for a cheap chunk of H07RN-F, and with no delivery charges which is always nice!

The SY cable is attractive but seemed to have a thicker OD than the H07 for the same wire size. I guess that's to do with the internal braiding. I thought that might compromise its flexibility a little, but I may be wrong. Sometime I'll get a small piece and see - nothing like hands on. Perhaps because SY is not officially for 'power' applications, it didn't have the correct BROWN BLACK GREY core colours as mentioned by Andrew J. Not that this is hugely important, just nice to have some order in life

Gerry

ps, Just noticed from Roberts latest link that the SY can have the 'correct' colour codes (described as 'also available' ) Nothing is ever certain in life is it

Edited By gerry madden on 18/09/2022 18:39:16

Edited By gerry madden on 18/09/2022 18:40:05

BS 7671 requires that the cables comply with relevant standards which could be British Standards or equvalent. SY cable does not have a particular standard. However it is widely used in industry for final connections to machines where inverters (VFDs) are used to control motors. The reason is that the braid on ST cable is earthed and helps to minimise the noise caused by the VFD which could affect other equipment.

SY is a useful cable but should not be considered as an armoured cable as the braid in not as tough as the steel wires in an SWA cable.

Yes, the cores are all black and are numbered but coloured sleeve could be used to identify the cores as Brown, Black and Grey.

Special brass cable glands are available terminating the cable but, in many cases, I have seen plastic stuffing glands used. It is important that the braid is earthed at the origin of the cable and that the terminations are not put under strain if the cable is pulled.

Edited By Richard Taylor 17 on 18/09/2022 21:13:10

Your statement contradicts the link posted above pointing to Cleveland Cables site where it says the cable is made to BS EN 50525-2-11.

Your statement contradicts the link posted above to RS site where it says the correct cable to use if you want to minimise electrical noise is CY (not SY).

You earth the braid on the cable so that if it is damaged and a live conductor from inside the cable touches the braid, it cannot become live and kill you if you touch it.

The really important bit for people to know in all of this is that the braid is not sufficiently sized to act as the CPC (protective earth) and in addition to earthing the braid, a dedicated earth conductor must be provided in the cable itself.

I have seen too many installs where it's been assumed that you can use the braid of SY in the same way as you can the armour in SWA.

.

In any case the use of SY (or other non-standard cables) is to be discouraged unless there's a good reason to do so (and in doing so deviate from BS7671), as documented by the designer of the installation.

This document from Eland Cables explains the situation with respect to BS EN 50525-2-11 (which is a standard for how one makes cables generally, not a standard specifying the design of a particular type of cable) not translating into 18th edition compliance without further consideration.

Edited By Jelly on 18/09/2022 23:49:33