Tools & Installation


Apart from normal hand tools to attach the boxes and cable to the wall you will need an insertion tool if you are using IDC connector boxes.  Using the right tools IDC are much more reliable than screw connector boxes.

When using IDC connectors do not strip the cable ends, the insulation is pierced by the blades in the socket and is needed to ensure a sound joint.

Shown  on the left is the correct tool to use, unfortunately they are expensive, about 20, but well worth getting if you have much cabling to do (they work for Cat 5 network cabling as well).  We sell these.

Below the proper tool is the nasty plastic thing supplied with sockets or sold for a few pence.  I have never had much success with these.  Even used with great care they are only good for about 10 to 20 insertions (that individual terminals not sockets - so about 2 sockets and that's your lot).

In the past I've made ad hoc tools by taking a small screwdriver and cutting a slot in the middle of the blade with a  Hacksaw.  Not as good as the real tool but better than the plastic one although it takes a bit more skill to align it properly. DONT try to push the wire in with a screwdriver blade without a slot, you will simply push the IDC blades apart and make an unreliable connection.

Incidentally IDC connectors should ideally only ever have one wire inserted, certainly no more than two and both should be idenitical diameter solid cored wiring.  Don't mix telecom cable and Cat 5, they have different diameters and mixing them in the same blade makes the joints on one of the wires unreliable.     For this reason extension junction boxes should be used to join cables.

Avoid using stranded (alarm) cable with IDC connectors meant for solid core telecoms cable.

IDC proper tool
IDC plastic thing
How IDC Works


This is the easy bit.  Just remember to connect all the numbers together, so 2 to 2, 3 to 3, 4 to 4 and 5 to 5.  Connectors 1 and 6 have nothing to do on a plain telephone circuit.


Make sure you use telecoms cable (single solid core) and not alarm cable (different colour code and stranded wire),  Alarm cable is not twisted in pairs and has quite poor noise immunity compared with telecoms cable.  It also won't reliably fit in IDC connectors.  Cat 5 cable, if you have it, is nothing more than very upmarket and expensive telecoms cable and works fine (and gives you spare wires!).

It is important (especially for modem use) to ensure you keep pairs together.  Telephone cables rely on having pairs twisted together to reduce noise so pins 2 and 5 should always be on matching colours (ideally orange/white, acceptably blue/white) NEVER blue on one and orange on the other.

DON'T cross any wires - crossing 2 and 5 for instance (so 2 in one box goes to 5 in another) creates a situation where either socket will work by itself but once a phone is plugged into both they will either continuously ring or not work.


A common complaint is that one phone will work in an extension yet another plugged into the same socket won't.  Usually this is because either the extension has been wired up with only terminals 2 and 5 connected or 3 has come adrift.  Some phones originally designed for the overseas market will accept a ringing signal on 2 and 5 only (they usually only have those two wires connected) and so will work, others designed to use pin 3 for the ringing circuit won't ring but they will dial out and you can speak on them.

IDC junction box

IDC Junction box

These small boxes (about 1" by 1.5") are used to join cable.  Pin 1 on the left is connected to pin 1 on the right and so on.

Note the placing of the wire from the inside going out in the connector.  This is the correct way of fitting it.

Junction boxes come in varying sizes from 4 pairs to the 8 pair shown.  I tend to always use  8 pair, they cost only pennies more than 4 pair and are useful if you need to add more later.

Fault Finding

No ringing

Terminal 3 disconnected

Phone ringing continuously

    Terminals 2 and 5 swapped (2 at one socket connected to 5 on another and vice versa)

Very poor speech quality, possibly poor bell.

Terminal 3 and 2 or 3 and 5 transposed

Ringing but no speech (or very poor speech) and can't dial out.

Wire between terminals 2 or 5  broken.


Testing the cabling

This is terribly obvious once explained (and not so obvious beforehand!)

You have an installation where the main socket works and the remote in the garage roof doesn't.  You need to test the continuity of the circuit.  So you can get a verrrry long lead for your test meter - or cheat.

  • Firstly, disconnect the BT line completely.
  • In the remote end bridge any two terminals (make a note of which two).
  • Measure continuity between these two wires at the master socket end - should be no more than a few ohms.
  • Repeat for the second pair of wires.
  • If either show a fault swap the combinations - so if you tried 2 and 4 and that was OK, and then 3 and 5 and that failed, you know 2 and 4 are both good so trying 2 and 5 and 2 (or 4) and 3 will show you the faulty wire.


OK - so you have tested the cables and there is 150 yds of cable buried in the newly decorated wall and only 2 wires have continuity - what do I do??

This is about the only occasion where you cheat and use a second master socket.  Ideally you use one designed for PABX use but beggars can't be chosers, it's normally 19:30 and mother in law is due to arrive in twenty minutes.  Nip down to your local DIY shed and buy a MASTER socket.

The second master gives you back your ring signal so connect the two working wires to terminals 2 and 5 on the new master and hope for the best!

Ringer Equivalence Number (REN)

REN measures the load a device places on the line when ringing.  A normal BT line will support a REN of at least 4, in other words at least a total of 4 phones/fax/modems should work on any line so long as their REN figures added together don't exceed 4.  The REN is normally found on a label at the base of the machine (near the green approval symbol).

In practise you can quite often exceed this number because devices with an REN of 1 may actually have a real REN of only a fraction of 1.  This is an anomaly of the test procedure used.  Moreover many lines can drive an REN of more than 4.  Note that some elderly fax and answering machines can have very high REN's (and they really are high!).  If your phones all don't ring, or some ring very anaemically then its possible you have exceeded the REN.  Try unplugging devices until they work.  You can get REN Boosters which will increase the ringing capacity of a line if desired, although if you get to this stage you should probably be thinking of installing a small PABX.

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