3 core SWA cable colour coding..

[tony sayer]

Cut a very long story short;!. We need to tap of a small amount of power from a county car park lighting system for a CCTV unit. This is fed with a 3 core SWA cable where they have the three conductors arranged as;

Red = Switched Live

Yellow = Earth

Blue = Neutral

They have a box which has a photocell and infra red detector arrangement that switches the live line to power the lights. What we need is a continuously available mains supply at one end of this lot around a 100 metres away.

Question..

Is it OK to change this so that the Yellow now carries the live or swap that for the Red and make the Yellow the switched live and use the Steel wire of the SWA cable as the Earth protective conductor?..

So now this becomes;

Red = Permanent live

Yellow = Switched live

Blue = Neutral

SWA wires = Earth

And of course label it all to denote that one is switched and the other is live etc?..

Cheers..

[Tim S]

tony sayer coughed up some electrons that declared:

I think the real question is will the SWA be suitable for the earth provision? No problem that I can see with the alterations to the use of cores - just sleeve red and black as appropriate.

The answer is probably. How big is the cable and can you estimate how long the longest run is, back to the breaker? What is the breaker (type and amps) There's some stuff in the Wiki that covers some of this.

Your stated colour scheme is quite sensible (= predictable to the future uninitiated).

Also, do all the existing lights reliably have the cable armour made off properly *and* is the armour connected to the earth terminal and/or metalwork of the lamp (if any)? They might just have earthed the armour at the feed end, if they knew they were going to use one of the cores as the CPC...

Sure there might be some more gotchas - hang about for some extra opinions...

Cheers

Tim

[Dave Osborne]

Sounds good to me. I wonder why they didn't use two-core SWA in the first place? Good that they didn't, hey?

You might need to get your knickers in a twist with labelling dual colour schemes if your new cabling is brown/blue or brown/black/grey...

[Owain]

As what Tim S says.

Suggestion - are the car park lights on often and long enough to recharge a battery at the CCTV location?

Is the CCTV cabled or wireless? If cabled can it be powered through the video cable - it could easily if it was an IP camera - PoE

Owain

[John Rumm]

Check this has not been paralleled with the armour!

Sheath with appropriate a colours and it ought to be ok. You will need to check the earth (i.e. armour) continuity.

More relevant stuff here:

?title=Terminating_SWA

[george (dicegeorge)]

It would work but it would be illegal in my opinion.

Use of a battery which charges when the lights on sounds the best idea to me.

[g]

[John Rumm]

Which bit? and illegal why?

[nightjar]

That is three-phase cable (old colours) and the sheath would have been the intended earth connection had it been used for three-phase. Provided the connections have all been properly made, there would be no problem with your suggested changes. I would put a red sleeve over the ends of the yellow wire, in case any of the labels come off or become illegible.

Colin Bignell

[george (dicegeorge)]

I had assumed the yellow was designed to be an earth, and the casing for physical protection, but now I realise I was wrong, the 3 wires were all designed for live 3 phase, so perhaps it is OK, if all the connections are changed and checked.

whoops

[g]

[Tim S]

george (dicegeorge) coughed up some electrons that declared:

Yes - that main thing is that the armour has continuity to all parts where a CPC is expected (as I said previously) *and* that the L-E resistance (R1+R2) is sufficiently low that on a L-E fault, th ebreaker opens within the correct time which is either[1] 0.4s or 5s depending on circuit function and type/size...

Usually this works for smaller sizes of SWA but I'd hate to take things at face value, which is why I asked if the max circuit length, SWA size and breaker size/type are known :)

[1] There's a 3rd timing, IIRC, but not one that's relevant to me right now so I've forgotton.

Cheers

Tim

[ARWadsworth]

[tony sayer]

OK thanks to all who replied..

No, the lights aren't on long enough for battery charging and we have tried that as one location does have a lump of CAT 5 cable which is pushing the length for the CAT 5 spec at 115 metres and thats through a very thin duct and it only just went in there with no problems to get power or another cable is a no go..We tried POE but the drop is too great even at 50 odd volts..

And we need mains volts for the cameras at different voltages and for a remote network VCR and a wireless link, we could I suppose have a collection of DC to DC converters but its all messy and whenever you just need mains to plug in the test monitor!...

The "3 conductors and sheath earth" principle is a good one so thats fine, in fact we'll more then likely have spare earth stake or so in order to cope with lightning discharge potentials as this is in a hilly place;!

The switched line is fused at 16 amps due to the 2 kW lighting load and I think the cable is pushing it for that spec anyway!

In fact where this comes off the SWA cable they who put it in originally have just used twin and earth to feed the lights with no extra protection so we'll sort that and this being publicly accessible too!..

But the continuous live will be fused at 6 amps as were never likely to take more than a half amp off it anyway and the whole will be on a RCD as muggings will be working on this alone .. and out in the wilds so;))

And what does the team think re the actual old cable colours and sleeving it with the new ones?.

It would seem more logical to me to have Red as live and Yellow as switched live..

Is there a colour code standard for this anyway live line and switched in this sort of allocation?..

cheers...

[David Hansen]

On Sat, 20 Jun 2009 12:46:34 +0100 someone who may be tony sayer wrote this:-

The joints are made outside the lighting columns? In what and mounted where?

I suggest that you test the armour carefully with a proper tester, to make sure it is up to the job.

I would sleeve the cores in the correct colours, rather then harking back to the days of old.

I would sleeve them both in brown. I would use the red as the permanent live and the yellow as the switched live.

[tony sayer]

In article , David Hansen scribeth thus

The lighting "columns" are in fact old telephone poles and are 20 foot high. They had to use them and limit the height at the insistence of the planners who have a thing about light pollution;!..

The lights are identical to the halogen floodlights that you'd have at home. But without the switch. Two on the one pole one on the other.

The cable/s come from underground clipped to the wooden pole then into small plastic encloses, the cables to the lights are done in 1.0 mm T&E just clipped to the poles with no extra protection..

Indeed..

Right tho that doesn't sound too logical, or does one assume that both are to be treated as live?..

[tony sayer]

OK according to their cable calculator this setup is from electricity supply in a small brick built housing to the first light pole is 20 metres..then another pole 70 metres, and the CCTV supply a further 10 metres.

Total load for Three core PVC SWA which in effect will be two core is 1.5 kW total load plus the 10- watts for the CCTV .. but as only 1 kW of light is on that pole then thats all OK for that bit as the existing cable is 1.5 so thats a max load capability of 3.5 kW over 20 metres so assume a total load capacity of say 2 kW then to the first pole thats well within .. the second pole will draw 1 kW well 500 watts of light and a max of 500 to the other equipment which will be far less then that..

So 70- metres from the fist pole will still be within the capabilities of the

1.5 cable?.. which is taking 2 kW from the supply to the first pole then 1 kW of light on that then a further 70 metres to the second pole with a 500 watts light load and up to say 500 watts absolute max for the other equipment?..

What do Queens regs say about that end having a an isolator and a single MCB of say 6 amps feeding a dual 13 amp outlet socket not that anyone would plug any more load in that then say 100 watts total?..

If it were possible to connect the gear in there directly to a cable outlet then I'd do that but as their bloody wall warts .. not possible;(..

[tony sayer]

OK according to their cable calculator this setup is from electricity supply in a small brick built housing to the first light pole is 20 metres..then another pole 70 metres, and the CCTV supply a further 10 metres.

Total load for Three core PVC SWA which in effect will be two core is 1.5 kW total load plus the 100 watts for the CCTV .. but as only 1 kW of light is on that pole then thats all OK for that bit as the existing cable is 1.5 so thats a max load capability of 3.5 kW over 20 metres so assume a total load capacity of say 2 kW then to the first pole thats well within .. the second pole will draw 1 kW well 500 watts of light and a max of 500 to the other equipment which will be far less then that..

So 70 metres from the fist pole will still be within the capabilities of the

1.5 cable?.. which is taking 2 kW from the supply to the first pole then 1 kW of light on that then a further 70 metres to the second pole with a 500 watts light load and up to say 500 watts absolute max for the other equipment?..

What do Queens regs say about that end having an isolator and a single MCB of say 6 amps feeding a dual 13 amp outlet socket not that anyone would plug any more load in that then say 100 watts total?..

If it were possible to connect the gear in there directly to a cable outlet then I'd do that but as their bloody wall warts .. not possible;(..

[David Hansen]

On Sat, 20 Jun 2009 14:49:41 +0100 someone who may be tony sayer wrote this:-

I would replace them with high pressure sodium lights, powerful enough to get the necessary light level for the CCTV in the whole area. I assume the CCTV is not infra-red.

The lights will presumably be left on for long periods with CCTV, in which case (as well as making the electricity meter spin round quickly) they will need to budget for someone to constantly replace the failed lamps. Having lamps come on suddenly will probably cause the camera trouble for a few seconds, probably at the worst moment.

Is the continuity of the armour maintained across the small plastic enclosures? If not then after the first plastic enclosure the armour is floating.

Hmmmm. I would either fit conduit, or replace with cable suitable for outdoor use.

It sounds logical to me. One will be live at all times, the other will be live when the lamps (either the current ones or new ones) are energised. Whether there is a detector or photocell energising this wire I would treat it as live at all times, unless I had taken steps to make sure it cannot be energised.

Brown, black and grey (and numbering systems) are used to differentiate between different phases on multi-phase AC circuits (for DC circuits they do much the same thing). You are working on a single phase circuit.

[John Rumm]

Yup, if you just want live, neutral and earth you would usually use a two core swa and use the screen as the earth. Some applications may however require use of a core in addition to the screen. The colours are frequently not what you would ideally want and will need over sleeving.

Its a particular nuisance when you have a mixture of old and new colours as well as a mixture of two and three core, where you notionally have black and blue both potentially being line and neutral. (in these cases I sleeve new cable to match the old colours)

[<me9]

Metal halide wuld give a more natural colour rendition, akin to the existing lights, but would have a lot of the advantaged of the sodium lamps. They would probably give less light spill, and please the planning authorities and neighbours.

[John Rumm]

So we have :

----20m---------P1-------70m----------P2----10m-----CCTV

Is it 1kW on pole 1, 500W on pole 2, and an allowance of 500W on the CCTV?

Voltage drop is an issue here. With 1000W load (4.35A) at P1 you have

2.52V of drop at that pole. With 500W (2.17A) at P2 you have another 4.4V of drop there (assuming a drop of 29mV/A/m).

So by the second pole you are already a little under spec on voltage to be strictly in compliance with the regs. In terms of cable carrying capacity the cable is fine.

You need to check disconnection times as well. What earthing system is at the head end of the cable?

As long as you label the socket appropriately you should be ok.