Screening control cables

[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

 

[sysrq]

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

In general ferrous metals like steel are prone to formation of eddy currents which generate heat especially at the VFD harmonic frequency range, roughly from 4kHz to 30kHz.

 

[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.

Even when the same symmetrically arranged cable or coaxial cable is squeezed at one point then good standing wave ratio can be ruined.

 

[edexlab]

Had a good look at the CY screen today and it is copper, from the look of it and the way I blunted my snips I thought it was fine steel wire!
Think I'm going to return those side cutters!!!

 

[shanky887614]

Had a good look at the CY screen today and it is copper, from the look of it and the way I blunted my snips I thought it was fine steel wire!
Think I'm going to return those side cutters!!!

pound land special?

bahco hdg or knipex snips (160/180mm)

behco hdg snips are rated to cut piano wire and they can cut small chain down easily as well

 

[edexlab]

These are Bahco I don't buy cheap rubbish from eBay or anywhere else, I expect tools to last and don't mind if the price matches!
I've not had them long and only cut control cables and flexes with them I use a different pair of croppers for steel braid

So they're going back I'll try another pair just in case they're a dodgy batch, quite disappointed really as I do like this brand!
Although their customer service isn't great......
Recently I enquired direct about a replacement box for the 1/4" socket set I've had for 4/5 years the hinge wore out, so I contacted them re buying another to replace it,the guy said they didn't sell them and he'd see if he could sort one out for me ,I've emailed him several times with no response at all, which is pretty poor I think !

 

[shanky887614]

These are Bahco I don't buy cheap rubbish from eBay or anywhere else, I expect tools to last and don't mind if the price matches!
I've not had them long and only cut control cables and flexes with them I use a different pair of croppers for steel braid

So they're going back I'll try another pair just in case they're a dodgy batch, quite disappointed really as I do like this brand!
Although their customer service isn't great......
Recently I enquired direct about a replacement box for the 1/4" socket set I've had for 4/5 years the hinge wore out, so I contacted them re buying another to replace it,the guy said they didn't sell them and he'd see if he could sort one out for me ,I've emailed him several times with no response at all, which is pretty poor I think !

which bahco snips?

i use these and they are very good 20hdg

 

[edexlab]

180 ergo

 

[shanky887614]

180 ergo

take them back if you can, the hdg can cut a lot harder metal and cost about £20 on amazon etc

 

[sysrq]

In general ferrous metals like steel are prone to formation of eddy currents which generate heat especially at the VFD harmonic frequency range, roughly from 4kHz to 30kHz.

Actually, as far as I ''know'' it's more of an issue with single core cable and steel armour, with multi-core cables it's not so significant cause electromagnetic waves induced in steel armour from two conductors cancel each-other out.

How do you normally terminate the pigtail of sy cable steel armour to commando plug at the supply end only to protect against cable mechanical damage?
I couldn't find anything about connecting two dissimilar metal wires (green-yellow earth conductor with galvanized steel armour). I think crimping them in to one ferrule is not the best thing do.
The pigtail should be as short as possible to reduce inductance, only thing is it depends on frequency range you want to screen against with considering that steel works better at low frequencies. SWA cable steel armour is connected at both glands cause there is a 360 degree connection. If you don't have a EMC grade glands for sy cable then there is no other choice but to use pigtails and connect with short one only at the supply end to avoid ground loops.