Repairing low voltage cables (computer, phone etc)

[listerofsmeg01]

Hi all,

Can anyone give tips on repairing such cables?

In the past all I have done is strip back the insulation, twist each inner copper pair together and insulate each pair, and then the whole lot with electrical tape.

The problem with this is that once a pair is twisted together, I have to bend the twist back against itself in order to lie flush against the wire (ie when I twist them, the twist is perpendicular to the run of the wire). This doesn't seem good practice somehow, so I wondered what the correct way to repair such things was.

Also, any advice on stuff like USB cables which have thin metal shielding running just inside the outer insulation? Will lack of shielding in the repaired section cause problems?

Thanks, Lister

[Peter Crosland]

Repairing any screened cable ifs difficult and is unlikely to be satisfactory in the long term. USB cables, particularly USB are very well screened which is one reason they can carry data much faster than USB 1. Buy a new one.

Peter Crosland

[Ian Stirling]

It doesn't really matter.

Soldering, then insulating can leave a neater join.

Usually it'll work - mostly. However, for high speed stuff - USB2/firewire/ and the like, it may well be very unreliable. Or just marginal, and stop working for no apparent reason in a few months.

[Brian Reay]

In general, I'd recommend you replace rather than repair. However, if you must repair, use a length of "heat shrink" before you strip the two parts and lay the conductors side by side and solder. Slip the heat shrink over the joint and heat to shrink.

For screened cables, fold back the screen, treat repair as able, then fold screen back over the heat shink. Make sure the screen overlaps well and use more heat shrink.

However, these are temporary / emergency approaches in my view.

[Jason]

Probably the *most* correct way of repairing them, is not to. If you can replace the run of cable with a new run, then that would be the best choice for safety, mechanical strength and reliability.

-- JJ

[The Natural Philosopher]

take each strain, and slip a bit of heat shrink over one of the ends to be joined, and twist together 'in line' and SOLDER. then use the heatshrink to insulate the individual strands, and tape the whole lot up afterwards

Twisting wires together is not good practice - corrosion generally gets you in the end.

[The Natural Philosopher]

The actual effect of a short length on unscreened is not great. Especially if you wrap it with wire or something conductive afterwards to 'repair' the screening.

A lot depends on what sort of cable it is: If the screening is to reduce interference, then that is more than good enough. If it is an RF cable then you will get small reflections off the join, and this will lead to slight gain variations with the wire length and frequency. In non critical applications that is not a big problem. In critical ones it may be. I wouldn't for example care to do that to a satellite down lead.

[Graham]

As you say, not good practice, but it works fine, and my floorboards conceal several such bodges.

[John Rumm]

USB 2.0 at 480 Mbps would be well into "RF" I would have thought!

[Owain]

The correct way is to twist the wires together along the length of the wire, and stagger the joints so you don't end up with a big bulge.

site: ignore where it says "Wire nuts are acceptable for home applications")

[Terry]

You make it sound as if this a frequent occurrence as far as you're concerned! Can't you fix whatever is causing the problem?

Cables which are twisted or screened are made that way for a reason and it is best to either replace the cable or fit the correct connectors and couplers to maintain the integrity of the cable. They will also give you peace of mind if they are hidden!

An exception here is telephone wiring as the twist is minimal over a short distance and signal frequencies are low (unless your running ADSL over it!)

You might not be so lucky with CAT 5E Ethernet cables though!

Terry

[Harry Bloomfield]

[e-mail] formulated on Sunday :

Rather than twisting them at right angle to the cables, you could do an in line splice. Put one end along side the other without bending them, so that the two ends face towards the far end of its opposite number, then twist them, even better add a small blob of solder to the joint to make it more reliable.

If jointing more than one wire, space the joints out such that none is next to another one. A single layer of tape is usually enough to insulate between cores, then a layer or two over the top of all of them.

[meow2222]

Thats nuts, wire they recommending that?

NT

[The Natural Philosopher]

Yes, but its a lot higher power. A bit of loss here and there won't make it too bad.

Its when your data is encoded into very subtle variations in phase that you get into trouble. You probably don;t even WANT to examine how a DSL modem works...