Ethernet Economiser

A pair of ethernet economisers allow two 100Mb/s ethernet clients to share the same cat5/6 cable. The application is where a single ethernet cable is already in place between a switch/router and a remote device, and you want to add a second device local to the first but without running a full cable all the way back to the router / switch.

It does this by exploiting the fact that a 100Mb/s connection only uses two pairs of the cable so providing the cable is fully wired with four pairs then two connections can go down the same cable. If your devices use Gigabit (1000Mb/s) then that needs all four pairs. The economiser would still work but the speed would revert to 100Mb/s.

Commercial economisers are available fairly cheaply, but they are configured as two ethernet sockets onto 1 plug. This may suit some applications (e.g. where there are wall outlets and a central patch panel). In my set up I had a regular ethernet cable in place terminated in plugs so I would have needed lots of extra patch cables and Ethernet joiners if using the commercial versions.

By constructing as a single rj45 socket to dual plugs I minimised the extra cabling required. At the router end, the existing cable is unplugged and put into the economiser. The two plugs then go into two ports on the router. At the other end the cable is unplugged from one device, and put into the economiser and the two plugs then feed two devices.

Parts for one economiser end. Two required for a connection.

1. RJ45 punch down socket (1)
2. Tie wrap (3)
3. Ethernet cable (solid wire preferred)
4. Ethernet RJ45 plug (2)
5. Enclosure ( I use 3d design https://www.thingiverse.com/thing:2601362)

Tools

1. Punch down tool
2. RJ45 crimper

Making up the RJ45 plugs can be avoided. by cutting an existing RJ45 cable in half. Solid wire is preferred by the punch down sockets. Wires can be pushed down into a punch down socket using an improvised tool but a dedicated punch down tool makes it much easier.

The lengths of the cables for the economiser at the router switch end can be kept short as they will plug into nearby ports.

The lengths of the cables at the device end can be chosen to suit the separation between the local devices.

If using the 3D printed enclosure then the punch down socket just inserts into the enclosure and is twisted down to secure on a back ledge. Double sided tape can be put onto the base of the socket before inserting to make it secure.

Feed the cut ends of 2 cat5/6 cables through the holes of the enclosure. Strip back the sheath leaving about 4cm of inner wires exposed.

Cut the blue and brown pairs off at the start of the sheath. Only the orange and green pairs are used in each cable.

Clamp a small tie wrap near the sheath on each cable and pull the cables back so the tie wrap is back against the side of the box.

Untwist the pairs and wire into the punch down socket using the punch down tool. The socket will be marked on the side with two colour schemes marked A and B. Use the B scheme.

One of the incoming cables should go

• Orange -> Orange
• Orange-White to Orange-White
• Green -> Green
• Green-White to Green White

The Other cable should go

• Orange -> Blue
• Orange-White -> Blue-White
• Green -> Brown
• Green-White -> Brown-White

A tie wrap on the outside of the box tying the 2 cables together makes it more secure.

If using the 3d printed enclosure then slide lid on to complete the box.

Unplug Ethernet cable from switch or router and plug into socket of one economiser. Insert the two RJ45 plugs into ports of the router or switch.

Unplug Ethernet cable from existing device and plug into a second economiser. Insert the two RJ45 plugs into the two local devices.