I’ve noticed that the query “How To Wire a Master Socket” crops up frequently on Google.

We’ve blogged on this topic in recent times, so it might be worth taking a look here,too.

As a telephone engineer, it would pay me to make things very complex and difficult for readers, and make it clear that this is a job for “the professionals”. Don’t worry – I won’t.

However, I need to make it clear that strictly, the master socket is property of Openreach. I have blogged on this topic here and here. In theory, no-one should touch it. Meanwhile, in reality…………………. (hello??)…..

Before I Start (Tools, Cable and Voltage)

You will need a proper cable insertion “punch-down” tool to push down cables onto terminals.  These are available on eBay/Amazon – (search for Krone Tool, insertion tool). Don’t use a screwdriver blade – you will damage the connectors!  I have blogged on cable and jointing here and here.  Hazardous current?  Measured in Milliamps. Only enough to give you an occasional “tickle”.


Down from a Pole, or Up From a Hole. What Goes in The Back?

This is how your telephone/broadband service arrives on your property, via a single pair of wires, each containing half a millimetre diameter of copper. Amazing. I’m surprised it ever works as well as it does. These need to go on the back of your socket.

Exactly “Where” On The Back?

On the very back face on your master socket are two terminals marked “A” and “B”. The wire goes here. It doesn’t matter in which order.  Old-style sockets have screw connectors.  Later ones have punch-down or plastic-lever-type connectors.

Help! So Many Colours….

(Don’t worry – it’s fairly logical.)

Colours:- from an underground cable. These are “paired” as “plain blue-plain white”, “plain orange-plain white”, “plain green-plain white”, “plain brown-plain white”, “plain grey-plain white”. It is probable that your service is on the “blue” or “orange” pair. Important – the corresponding white wires can only be identified by whatever colour they are twisted around. Therefore, take care in unbundling them. However, fear not – if you mix them up, simply swap the white ones around until you hear a dial tone.  Much more on underground cable here. 

Colours:- from a pole. Orange and white (normally used first), then green and black. More on “drop wire” here.

What Goes On The Front?

By “front”, I mean the detachable bit of your master socket, usually the bottom half, but occasionally the whole front on newer ones.

Here you will see some punch-down terminals numbered “2”, “3”, “4”, and “5”. In most cases, you only need to add any extension required to “2” and “5”. Use the “blue/white”- “white/blue” pair of cables for the sake of convention.

Wait a Minute! – There’s a Couple of Terminals Marked “A” and “B” On The Front.

Yes indeed. On some newer sockets, you’ll find these. They provide a filtered broadband output. Use high-quality cable (such as Cat 5 or Cat 6 data cable)to where you want your internet router to be, and you are making the very best use of your broadband. More on this here.

That’s about it. Very occasionally, your cable from outside will be jointed before it gets to your master socket. Normally you can find a connecting box where the transition from the exterior cables to the interior ones is made. The convention is to use the “blue/white”-”white/blue”. Very occasionally, with either very old or very new cabling, a “blue/orange” pair will be used.

It’s Not Hard!

Trust me, it’s simple if you take your time and don’t panic. You can’t break anything. There won’t be a call from The Socket Police. If the exchange building catches fire, you won’t have caused it.

However, we do not suggest that you interfere with Openreach’s property.

Meanwhile, if you need help and are local, give me a call. If you are not local, drop me a line with your postcode, as I am in touch with independent engineers throughout the UK.

However, I can’t run a free help desk, so all I’d ask is that of this “How To Wire A Master Socket” guide has been helpful to you, you leave a very short review on Facebook or Google. Thanks.