Telephone cable stops working intermittently

[johncassell]

Hi all, we are using a Cat5 cable from the patch panel in our server room down to a little office for telephone purposes. The length is about 70 metres. The problem is this - on a morning our staff come in and this particular phone isn't working (faint crackily noise only). We only need to use 4 of the 8 cables inside the cat5 and I so I attempt to reseat the connections in the telephone socket box on the wall. This usually doesn't work. A day later I could try the very same thing again and the phone springs to life. The next morning (something seems to happen at night) the phone has gone back into its crackily state.

There is continuity in the 4 cables back to the patch panel and I know the port in the actual telephone system works fine (as if I plug a phone directly into that, then it works every time). Would anyone have any advice as to what could be causing this to happen? My boss suggested a dry joint so I cut the cable a bit further back and reseated back into the wall socket - I thought this had fixed it but next morning dead again.

Hope someone can help. thanks, John

 

[SLIPSHOD & SLAPDASH]

Try the other 4 cores.

Have you tried a different phone. Then try swapping the socket for a different one

 

[johncassell]

Hi, thanks for the reply.

Yes I've tried a different phone and a different socket. I've also attempted to try the other 4 cores but they don't work (and fail a simple continuity test)

 

[Andy™]

sounds like a damaged cable which would need either replaced or repaired

you say there is continuity, but are they shorting out?

 

[Evans Electric]

I'd say Andy has the answer there ,  if the other cores are damaged there probably an intermittent fault on the ones you are using.

Rewire the line .  

 

[johncassell]

Hi, thanks for these replies. Its quite a difficult route to re-run/replace this cable so I have to put that as a last resort. I'm a bit of a beginner when it comes to testing. How could I test to see if it is shorting out (heard the phrase but don't know what it actually means). John

 

[Doc Hudson]

Hi, thanks for these replies. Its quite a difficult route to re-run/replace this cable so I have to put that as a last resort. I'm a bit of a beginner when it comes to testing. How could I test to see if it is shorting out (heard the phrase but don't know what it actually means). John

How did you test the continuity you described in your opening post, if you do not understand how to test if something is shorting out I was wondering how you have managed to test the continuity? Or do you mean you just plug a phone in and got a tone? Do you have, or have you used, any test equipment of any sort?

Doc H. 

 

[Bruspark]

Notwithstanding the 'difficult route' if the phone handset works at the other end of the cable it is probably the cable and if some cores are faulty then 99% they are all intermittent or faulty.  Rodents, heat etc many causes.  Is a cordless phone not an option ? -  They go a long way if the base station is line-of-sight to the handset. 

Shorted out is indeed a bit meaningless - usually means two or more of the cores connected together via error or fault.  A simple resistance test meter can tell you if this is the case (disconnect both end of the the cable to test it or the  ~ 50V DC voltage on the phone line will cause confusion)

If you really have no option to replace the cable then use a terminal block to group 4 cores into one phone 'wire' and the remaining 4 cores as the other at each end.   i.e. each phone 'wire' actually travels over 4 cores.   (Do try to group the same ones!)

 If there is a short you need to ensure the two shorted cores are both on one 'wire'.  

 

[Sharpend]

As a thought, most cordless handsets need only two cores, so if possible change the phone to cordless?? 

 

[Andy™]

a corded cordless phone?

 

[Sharpend]

The digital phones only need two cores at the telephone point so if he has two good cores then problem solved, normal phones require 3cores. 

 

[Andy™]

a normal phone needs the 3rd core for the ringer. you can get round that problem by using 2 cores then fitting a master to get the 3rd core again

 

[Bruspark]

For lovers of detail /history /pedantry (guilty m'lud)

Actually the Need for the third 'ring' wire has died out over the years - It existed to ensure that dialing a rotary telephone did not tinkle other bells in the house.

For a while British touch tone phone makers continued to use it as the 'ringer wire' because  

a) the GPO said it should be so  

b) it saved a few components in each phone.  

Almost nowhere else on the planet did this - they all took the 75V AC ring voltage (and filtered out the tinkle before the 'sounder') from the A / B (numbers 5/2) 'voice' lines as was.  

So the US market / far eastern manufacturers had thus already ensured that their phones would ring from the 2 and 5 wires and the 3 (ring) wire if fitted was not actually used or needed.  It also meant they could ship their phones to more countries.

So it is 90% certain a modern phone would ring using a 2 wire cable carrying only connections from terminals 2 and 5 and near 100% certain any newly bought 'far eastern' phone will ring on 2 and 5.

There is no magic in the ring wire - it's a capacitor to the B wire and a resistor to the A wire and while these will pass the AC ring pulses down the ring wire they are not filtering anything from 2 and 5 in any way.  As others have said for the last few % of old/weird phones fitting a master at the far end (or indeed an ADSL filter) will recreate the ring line connection.  For ADSL use this is actually preferred as disconnecting the ring wire at the master socket balances the line in the premises.

 

[Sharpend]

As I said with the cherry on top !  :Applaud

 

[Blue Duck]

I do lots of extensions and have never used the 3rd wire, I understand it's best practice I don't see the point and don't get alloted a great deal of time for these jobs, never had any problems or complaints with my superior test equipment; an Argos value telephone and 17070.

 

[Evans Electric]

I stopped connecting the 3rd wire  years ago TBH  , as said , I too believe it was to stop bell style extension phones fom tinkling in sync . with the dial . 

Sometimes punch them down for neatness though.

Most phone wiring ends up with spare cores which can prove very useful for another line  or overcoming damage. 

Your PC uses just one core on the BT line I'm told.   So you can have a working PC but no phone.

 

[Bruspark]

Your PC uses just one core on the BT line I'm told.   So you can have a working PC but no phone.

Broadband is a more like a radio signal on both cores than power transmission.  I had just one of the 2 phone wires broken between the BT cabinet and my house.  No calls, No Dial tone or line voltage but still used broadband to report the fault !

 

[Evans Electric]

Yes , same here  thats how I found out . 

 

[SLIPSHOD & SLAPDASH]

Except, in this case its a system phone using 4 cores.