Screening control cables

[SheffSimon]

From some training notes...

Some drive manufacturers have recommended specialised cables using one or more braided copper screens. Measurements at Control Techniques have consistently shown that low-cost steel-wire armoured cable, as widely used in the UK, gives equally good results. The reason for this appears to be that although the steel wire is a less effective screen (Z[SUB]T[/SUB] is higher than for the copper braid), the losses in this frequency range are higher so that the actual current flowing in the screen is less.

Also,

http://www.brookcrompton.com/pdf-files/GAMBICA_Installation_Guide_Power_Drive_Systems.pdf also suggests that galvanised steel wire armour is an effective screen, and cables with open woven braids are not suitable.

I would class SY as an open woven braid......discuss

 

[Darkwood]

A good little link... points I noted .. SWA would satisfy only if tightly wound, very few SWA's meet this criteria and only the more expensive brands - I have been in debate not long ago about poorly manufactured swa where all the armour had clumped together instead of the usual small gap between steel strands and left a 10mm open unprotected area. So if you are going to use swa I can see it been acceptable but only on a tight wound construction.... as you rarely stipulate this or know what armour you will get (cheapest per meter wins) then I would say a lot of the SWA on the marker for LV applications would be unsuitable due to the competitive market and corner cutting to reduce manufacturing costs.

The braiding about open woven been not acceptable then yes... cannot argue that - some SY has very poor coverage , I do use the tight woven brands where the underlying insulation is completely covered.

 

[shanky887614]

dark isnt it only dw swa that would comply?

i havent seen any swa that has the armour all the way around except on old installs.


you can get sy with a black covering to offer uv protection but this would have to be a special order from the manufacturers

 

[netblindpaul]

OK, fair cop, I was always taught that SWA was no good, and as a manufacturer, we would not accept it for connection between our drives and motors, our documents forbid it.
However, I doubt that adequate EMC screening would be achieved with a "normal" SWA purchased from your average wholesaler at the moment in the UK, and installed by a "normal" electrical installer in the UK.
There is too much time pressure on them to throw it in rather than terminate it in accordance with the requirements such as that in the Gambica documents.

I would add that if you are going to connect a BS5467, (or a BS6346 which is no longer) cable to a vibrating device then you must ensure that the manufacturer agrees that the cable is suitable for connection to a vibrating device.

 

[UKMeterman]

The problem with steel wire armour is that it just forms a very long thin slot for the radio interference to leak through, any decent emc coverage is in the form of a mesh.

 

[Darkwood]

dark isnt it only dw swa that would comply?

i havent seen any swa that has the armour all the way around except on old installs.


you can get sy with a black covering to offer uv protection but this would have to be a special order from the manufacturers

As I don't use it as a choice myself so knowledge of it for this purpose is limited but do know some SWA is compatable although the cheap standard SWA you get everywhere IMHO wouldn't be good enough, you can also get SWA with integral screening but the cost is rising beyond simply finding an alternative method. A lot of my cables of choice are suitable for energy track and screened to the teeth and so many ranges and styles that all installs can be catered for.

 

[shanky887614]

As I don't use it as a choice myself so knowledge of it for this purpose is limited but do know some SWA is compatable although the cheap standard SWA you get everywhere IMHO wouldn't be good enough, you can also get SWA with integral screening but the cost is rising beyond simply finding an alternative method. A lot of my cables of choice are suitable for energy track and screened to the teeth and so many ranges and styles that all installs can be catered for.

nice, by dw i meant double wound. you get swa with a lot more steel in it than normal, personally i would like a screen but then my cable of choice is sy or twisted pair (belden 8760 etc)

 

[SheffSimon]

SY only goes up to a certain size range though I think, and the voltage rating is 300/500, a lot of customers won't accept that.

If you have got big motors on VSD's then what would you use other than 3 core SWA?

 

[shanky887614]

SY only goes up to a certain size range though I think, and the voltage rating is 300/500, a lot of customers won't accept that.

If you have got big motors on VSD's then what would you use other than 3 core SWA?

thats a big motor that needs bigger than 150mm 4c sy

 

[SheffSimon]

thats a big motor that needs bigger than 150mm 4c sy

True, but not uncommon on long conveyors on power stations, quarries etc. We have installed conveyors with 250kW and 355kW LV motors, currents up to 750A, on VSD's. Some long cable runs too, SWA's in parallel, and I've never seen any connected in SY. It would just not be accepted by the customer engineer, nowhere near robust enough in that environment.

We always run the protective conductor separately, so 3 core SWA's.

 

[Darkwood]

True, but not uncommon on long conveyors on power stations, quarries etc. We have installed conveyors with 250kW and 355kW LV motors, currents up to 750A, on VSD's. Some long cable runs too, SWA's in parallel, and I've never seen any connected in SY. It would just not be accepted by the customer engineer, nowhere near robust enough in that environment.

We always run the protective conductor separately, so 3 core SWA's.

There are plenty of specialised cables for quarries, mines etc that you won't find in your local wholesalers, if you do this kind of work you will be familiar with the cabling used and how to source them, SWA as we buy at our wholesalers is just one type of many variants of SWA so to simply say SWA as a particular type of cable used is no longer enough info for the direction this thread is heading and more specific info is needed.

 

[shanky887614]

There are plenty of specialised cables for quarries, mines etc that you won't find in your local wholesalers, if you do this kind of work you will be familiar with the cabling used and how to source them, SWA as we buy at our wholesalers is just one type of many variants of SWA so to simply say SWA as a particular type of cable used is no longer enough info for the direction this thread is heading and more specific info is needed.

technically some cat5 is swa but not all swa is cat5


like dw says, ring the supplier and they will help you with a more speciality cable

 

[sysrq]

Only symmetrical conductor arrangement inside the cable should be used with the variable frequency drives, to avoid formation of standing waves and increased voltages. The same thing as with coaxial RF feeders (SWR meter, if reflected wave is higher than 1:1 then it gets inside the RF amplifier output stage which destroys the transistor or losses power and efficiency).
SWA steel armour is incapable of proper shielding against those awful harmonic frequencies asociated with VFD (kinda same effect like with sine wave clipping), so there is a reason why only silver coated copper shielding is used on proper radio frequency coaxial cables, or they use just thin flexible tubes with fine foam as an insulation.

 

[edexlab]

Just read your post sysrq on the other thread re SY cable braiding and noted what you said about CY cable which we use a lot at work for Emergency stops and some other signals etc, the CY we use has steel braid not copper? ??
I'm positive it's not tinned copper as I've blunted a pair of cutters previously on this cable, also the ends are not visibly copper
Are there different classifications of CY?

 

[sysrq]

Just read your post sysrq on the other thread re SY cable braiding and noted what you said about CY cable which we use a lot at work for Emergency stops and some other signals etc, the CY we use has steel braid not copper? ??
I'm positive it's not tinned copper as I've blunted a pair of cutters previously on this cable, also the ends are not visibly copper
Are there different classifications of CY?

Something about different types of metals for shielding. Steel braid is good for low frequencies. http://www.ets-lindgren.com/pdf/emctd_1293_weibler.pdf