In the process of decorating a room, I installed 2 elec sockets & an extra phone socket. The wires run fairly close and the phone seems to be getting interference from the power. Symptom: hum at ~~mains freq, louder when something is plugged in. I dont want to move the phone as this would mark walls & skirt board. Please any ideas on how I might shield? Thank you.
My computer telephone cable has a magnet around it - I have no idea what it does but maybe it is for interference?
Angela,
It's not actually a magnet, though it will look like one (!) - it's a piece of ferrite to stop interferance passing down the cable. Acts as a low pass filter stopping the high frequencies escaping from the PC and mucking up the telephone system.
Andrew Mawson
Did you use proper solid cored twisted phone cable? If you used alarm cables (stranded core) or the flat stranded core cable found in extension kits both are far more susceptible to mains interference.
You could put the phone cable in a soft iron pipe but realistically you can't shield the cable. The only real cure is to separate the phone cable and power cable. If you used any cable except the proper phone cable (or Cat 5) then redoing the run in the right materials would help - but I'd still take the opportunity to get the cables further apart.
First, ensure that you wired it correctly, so that the signal uses a twisted pair of connectors. You can't just connect any old wire to any old connector. The pairing of the cables is essential for noise rejection.
Then, at the master socket end, disconnect the bell ringing wire. This UK specific abomination, which isn't required for modern phones (which are designed to work in any country), leads to an unbalanced signal as it only uses one side of a pair. Unbalanced signals lead to noise.
Christian.
mucking up the
Thanks - nice to know how things work!
Are you sure about this, Christian. - I ask because my answering machine failed when I added an extension and I found out it was because I had accidentally dissed the ring wire, so the phone still worked, but didn't ring, I didn't spot it because the other phnoes did ring.
It's a fairly new DECT model.
Fortunately Argos accepted the new machine back as "not quite what I wanted...."
mike r
Whilst not altogether disagreeing with the sentiment this statement is, to be polite, hogwash. Many modern UK spec phones require the ringing signal on pin 3 to ring.
I've found it pretty rare in the last couple of years. No phone that I've bought recently has required it.
Christian.
Thank you who replied. I am not sure if it was the correct cable I will have to look. I think I recall that the conductors were thin, insulated in stripes blue/white orange/white etc and there were some not used.
Google found the WPP website which gives clear instructions.
bell) when someone pulse dials. It is true to say that most phones will work in two wires.
The original wiring of a phone circuit for multiple extensions involved special wiring and bells in series on effectively a separate circuit to prevent bell tinkle. The use of a third wire to carry the ring signal achieved the same result in a parallel circuit and allowed for much simpler and universal wiring.
Whilst many phones (and most modems) will work on two wire circuits it is by no means universal. Of half a dozen modern phones I have in the workshop less than half will ring on only a two wire circuit.
The easy way around this I've found is to wire two-wire, but to fit master sockets everywhere. Job done.
Hwyl!
M.
Others have mentioned separation for shielding, but how about for safety? If you have wired using a cheap extension kit, chances are that the insulation of the telephone wire isn't up to the job of being run next to mains cable - it needs to be mains rated unless it is separated by (IIRC) a minimum of 50mm or by a suitably rated insulating barrier...
Hwyl!
M.
But if you fit to many master sockets, you amy run into "ring trip"(*) problems or get the line logged as faulty by BTs automatic testers.
(*) Incoming call, all those capacitors take enough current to charge such that the exchnage thinks the line has been answered.
In article , Martin Angove writes
Since you can safely touch the insulation of the mains cable with your finger, I would say that the insulation on the telephone cable is of no consequence.
As far as it goes, the insulation on CW1308 is not mains rated. But the 50mm separation is more to do with physical damage and reduction in induced interference.
It doesn't need to be. The insulation on the mains cable is to protect users from mains voltages. The insulation of the telephone cable is to protect the user from telecom voltages.
No problem, and very valid.
I just said it wasn't 'unsafe' as was implied.
Except that it's what the Wiring Reglulations require...
You may disagree with the regulations. However, they do state that the telecoms wiring must be mains rated if it is to be run in close proximity to mains cables.
Christian.
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