Cable Question

[Rendezvous]

Hi All,

 

I have a brief question in relation to some cable I have been trying to source. I need to run it between lampposts. Here is exactly what I'm needing

Need to be Figure 8 Twin Core so I can tap into it using splice connections at various points

Has to be black (because I like black!) and to be waxed or coated to deal with outside weather and strain so it does not break or snap in the cold

Has to be strong and perhaps the cable being steel conductors instead of copper if it's stronger over distances?

 

I'm using it for stringing up some high impedance P/A speakers. I have seen other people use it but cannot think for the life of me what it's called or where to get it from?

Something around the 3amps mark sounds about right for ratings.

 

Thanks a lot in advance.

Josh

[david.elsbury]

High impedance??? Normally one would use 100v or 70v line systems for this application.

 

You could look up 'messenger wire' - this is the stuff with an integrated catenerary wire for suspension, I.e telephone lines.

 

David

[Dmills]

70 and 100V systems are both sometimes referred to as high impedance systems.

A 100V system running with 100W total load will after all by definition present a 100 ohm load to the power amplifier, a single 10W speaker would be a full 1000 ohms.

 

Possible google phrase "Drop wire", "CW1378", "Dropwire 10B" often comes with 2 pairs so fails your figure of eight requirement but meets the rest of it, and it is cheap (This is the stuff BT use from the pole to the house).

 

Regards, Dan.

[Owain]

BT Drop Wire No. 2 or No. 6 - specs CW 208 or CW 1247 - are copper coated steel figure-8 section with a rib for polarity identification.

 

http://www.caledonian-cables.co.uk/telephone/Indoor/CW1166.htm

 

 

[Rendezvous]

Thank you for all your replies.

 

Owain your near on the mark. just the stuff.. only problem, it just has to be multistrand, if the single core snaps for whatever reason? I am stuffed - Any other ideas?

 

Many Thanks.

 

I think I have found the solution. http://www.choulink.com/b2b_cpinfo.asp?id=36 and it would be the one on the left. Only problem is, it does not have polarity indication, but being telephone cable I would assume it would have something indicative? Thanks, Josh

[Shez]

Owain your near on the mark. just the stuff.. only problem, it just has to be multistrand, if the single core snaps for whatever reason? I am stuffed - Any other ideas?

If BT are happy to wire up umpteen million homes with the stuff, I suspect the risk of it snapping is pretty minimal...

[paulears]

With 100/70V systems generally used for systems with large distances between speakers - I've never given much thought to polarity due to path lengths being long enough to introduce far more delays than the polarity swap introduces?

[grizzly]

Only problem is, it does not have polarity indication, but being telephone cable I would assume it would have something indicative?

 

It may well have ridges or similar running down one side to indicate polarity.

Not too easy to tell from the bobbins picture on the website http://www.blue-room.org.uk/public/style_emoticons/default/smile.gif

[Rendezvous]

Thank you all so much for your responses. The drop cable it is!

 

Many Thanks.

Josh

[Owain]

The DW No. 2 or 6 have been superceded by No. 10 etc; I can't see No. 2 or 6. for current sale.

 

http://www.pmcteleco..._dw103250m/2708

 

If you are running over miles rather than metres then you may want to look at correcting for the transmission line impedance to prevent frequency distortion.

 

http://upload.wikimedia.org/wikipedia/commons/thumb/1/11/Transmission_line_element.svg/220px-Transmission_line_element.svg.png

 

If L/R = C/G then frequency no longer affects the calculation and matching to the line will work at all frequencies. Otherwise transformer matching to the line will only work at one frequency. Adding inductance of the value L=CR/G to achieve this. It is advisable to use lump loading in several places along the cable rather than one inductor at the end.

 

Depending on the layout of the area it may be possible to run the cable as a ring rather than a radial circuit, this will reduce the losses in the cable and also guard against a wire break. You might also want to fuse individual speakers as would be done in a voice alarm system, or to fuse at imtermediate points in the system, to prevent one speaker short-circuiting (or vandalism?) taking out the entire system.

 

Is this for temporary or permanent installation? Have you had any difficulty getting permission to use lamp-posts?

 

And remember, always wear a flat cap when up a pole ;-)

 

 

http://www.britishtelephones.com/gpo/overhead.htm

 

 

[dwright2104]

Owain your near on the mark. just the stuff.. only problem, it just has to be multistrand, if the single core snaps for whatever reason? I am stuffed - Any other ideas?

If BT are happy to wire up umpteen million homes with the stuff, I suspect the risk of it snapping is pretty minimal...

 

 

Our BT Line come into the back of the house and the external cable goes through two trees, and every 6 months or so BT are out to replace the cable.

[Shez]

Our BT Line come into the back of the house and the external cable goes through two trees, and every 6 months or so BT are out to replace the cable.

To be fair, being continually battered by tree branches is a tough job for any cable. Does it actually snap in the middle or suffer connection issues at one of the ends?

[kerry davies]

To be fair, being continually battered by tree branches is a tough job for any cable. Does it actually snap in the middle or suffer connection issues at one of the ends?

 

They wear out through friction rather than snap and noise and earth faults usually become apparent before disses occur. There is still AFIK a two-core dropwire called HV Blue (high voltage) which is good for this purpose but whichever DW is used the correct clamp needs to be used. See ebay for "curly wurly" or "pigtail" clamps.

 

Tree cutting was one of my favourite summer jobs and I spent many happy days up in my platform, elevating, No. 5, mangling foliage and renewing up to 80 spans of dropwire in some beautiful countryside. Damn sight better than carrying ladders across fields and rivers in February downpours trying to find a rectified short circuit.

 

Be careful when tensioning any dropwires, on longer spans and by tricks of the trade I could bend poles or pull the screws out of bargeboards with a single DW 10. They will easily pull over a scaff tower when winding them onto the clamps.

[Ynot]

Our BT Line come into the back of the house and the external cable goes through two trees, and every 6 months or so BT are out to replace the cable.

To be fair, being continually battered by tree branches is a tough job for any cable. Does it actually snap in the middle or suffer connection issues at one of the ends?

Indeed.

As Kerry alludes, the problems with tree 'damage' are usually confined to the insulation being worn down by the branches and causing partial and full short circuits due to direct contact and/or HR contact due to damp ingress etc. It's highly unlikely that a BT dropwire will break under far more than any reasonable use. You'd struggle to bend it with your bare hands, if I'm honest!

[Jivemaster]

ebay twin wire red black, black red speaker wire, over 1000 lots and cheap