DIY telephone wiring (Ireland)

[Adrian Brentnall]

HI Folks We're getting a 'real' telephone/broadband line installed in our shop in West Cork, Ireland.

I'm used to the UK / BT situation - where the telephone provider would normally provide a master socket.

Seems things are a little different over here - man I spoke to @ Eircom (telephone provider) said 'You have three lines going into the property' and claims to have re-enabled one of them for us.

Checking in the property, we do indeed have a 6-core cable coming in - and it terminates in a junction box, but not one with a phone socket. Eircom man said 'you'll have to wire it up to a socket - we don't do that'.

So - couple of questions.

a) To identify the 'live' pair - I guess I just look for a pair of wires with 50v across them ? True ??

b) I'll need to install probably 25ft of cable from the junction box to a phone socket. I have 'stock' of 6-way, solid core 'alarm' cable, as well as some 4-core stranded cable. I've seen mention of twisted pairs being used in 'proper' phone cable. Do I need to find some of that - or will either of the above cables suit instead?

Thanks Adrian

[Graham.]

True

Use proper twisted pair telephone cable, it's widely available. Solid core CAT5 network cable is also suitable. Twisted pairs help with immunity to interference originating externally. Google "common mode rejection".

[Frank Erskine]

The easiest way of doing that is to connect the +ve of your meter to a nearby earth, then probe with the -ve to find the "B" wire. Connect up the B wire to your meter, then probe the rest of the wires to find the "A" wire. You should find that the pair is lightly twisted together, and there may be some commonality in the colours, e.g. white/blue and blue/white, IYSWIM.

Avoid alarm cable. Since the wires aren't (normally) twisted into pairs you're much more likely to suffer interference, especially with a longish run as you describe.

Proper telephone cable is dirt cheap.

HTH -

[Bob Eager]

Just to add; don't attempt to use the stranded cabel, as it won't work properly in punch-down blocks (e.g. the phone socket).

[John Rumm]

I would expect so... if in doubt wire a phone across em and listen ;-)

Assuming you are fitting a UK style master socket, then you will need a solid core twisted pair really. Your alarm cable might do, but then again the proper stuff (CW1308) is cheap and usually easy to get (CPC have it)

[Mike Tomlinson]

En el artículo , Adrian Brentnall escribió:

Yes. You can use Cat 5 network patch cable as an alternative.

They'll work, but it's a bad idea.

[Graham.]

If you specify "patch" CAT5 you will probably get stranded cable, which, as John has pointed out is not ideal in Krone type connectors.

Mind you, it's not as bad as trying to crimp conventional RJ45 plugs onto solid cable as I often see people trying and failing to do.

[Dave Liquorice]

They must be doing summat else wrong then. I've only had one RJ45 to solid fail here and that's was because I got the plug on "upside down" so it went 87654321 instead of 12345678. B-)

All the Olympic Broadcasting Services provided commentary positions were connected via heavy duty screened solid Cat5 into RJ45's fitted on site.

Agree it's not recomended but it does work, just don't expect it to be as robust in repeated flexing as a stranded.

[Andy Burns]

Presumably fitted by someone who knew the difference between solid RJ45 plugs and stranded RJ45 plugs?

[Mike Tomlinson]

En el artículo , Dave Liquorice escribió:

There's two different types of plug - one for stranded cable and one for solid. If you look at the pins under a magnifying glass, the plugs for stranded cable have a pair of small prongs that pierce the insulation. I forget what the ones for solid cable look like.

If you use the wrong type for the cable you get a poor connection.

[The Natural Philosopher]

its worse. there are - or were - slightly different RJ45 plugs and sockets out there.

Fortunately they all see similar now.

[Dave Liquorice]

Nope, me(*) for the venue I was at. But then it was supplied kit of bits, drums of cable, bag of connectors... So one would assume the correct connector was supplied.

(*) Quick google later and I now know the difference. Stranded has two spikes in line. Solid has three spikes, the end two offset one way the center offset the other.

I didn't look *that* closely at the connectors supplied by OBS.

All the ones I've used here on solid cable are really stranded ones but as I say the only failure has been when I got the orientation wrong. They are all more or less static cables though not regularly moved, unplugged, plugged etc.

[Graham.]

I chose my words carefully and said *conventional* RJ45 meaning the more common type with the blade in line with the conductor designed to penetrate the insulation and conform the strands it mates with without cutting them.

You have to be quite lucky to get a reliable connection with them on solid core, mind you we did have a surplus of luck in the Olympics.

[Graham.]

Probably true for branded types you pay a resalable amount for. I have to deal with some cheap crap sometimes.

Last week I encountered some sockets that had an interference fit with the plugs I was using. In practice it meant I found it almost impossible to insert them by feel, and had to get into an uncomfortable position to see what I was doing.

[Bob Eager]

Apropos of not all that much (but given that there are a lot of ex-UKC people here), two of our CS students spent their Year in Industry working at the Olympics. A real plum job - they were Deputy Venue Technology Managers at the Excel and O2 (sorry, North Greenwich!).