Museum of Plugs and Sockets logo, small Fused Connection Units
for British ring circuits
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Fused connection units (FCU) are used for connecting permanently installed appliances to a ring circuit, or to create a fused spur (branch) from a ring circuit. FCUs are to be regardedas equivalents to a fused plug of a flex cord connected to an appliance that can be used anywhere.

Fused connection units are peculiar to the UK due to the need to fuse everthing down from the 32A ring circuit rating.

Images 1 - 2 show a FCU a modern model, bought in 2016. FCU's with a build in Residual Current Device (RCD) are available too. Classic models are shown in images 3 - 4 and 5 -8.


Fused Connection Unit with 2-pole switch and neon indicator light
Fused Connection Unit with 2-pole switch and neon indicator light

1, 2 Double pole switched fused connection unit with neon indicator light. Image no. 2 shows the reverse side and a scheme of the internal wiring (neon light not shown); DPS: double pole switch. Fuse: BS 1362 13A.
Manufacturer: Volex; initially a brand name of Ward & Goldstone. Details are given below.

Volex fused connection unit
Volex connection unit

3, 4

Interlocked fused connection unit made by Volex, probably in the 1960s. The fuse cannot be inserted or withdrawn when the switch is on (image no. 5), but the switch can be turned on with the fuseholder removed. This is fine because the contacts are touchproof. Interlocking is to prevent the contacts being made or broken under load.
Image no. 4 shows the unit with switch in off position. The fuseholder with BS 1362 13A fuse has been removed.

The Volex interlocked FCU is a part of the Electrokinetica collection. Images have been made by Lucien Numes.

Britmac connection unit, top view Britmac connection unit, bottom view

Britmac connection unit with switch in off position Britmac connection unit with switch in on position

5 Britmac earthed double pole switched fused connection unit, rated at 13A - 250V, AC. It has two contacts for a fuse unit with flat blade pins and an additional round pin. Fuse slots are 6.7 x 1.5 mm, with a center to center spacing of 19.5 mm.  Unfortunately, the fuse unit is missing. The connection unit has been saved during an upgrading project of an old hotel on the Isle of Wight.   {DF}
Information about the Britmac trade mark is given below.

6 Porcelain basal part of socket. There are five wire contacts. L (line) and N (neutral) that have to be connected to mains. L.I. and N.I. are outlets for the cable that is connected to the appliance. E = protective earth connection.
The indicated rating suggests 3 AMP 250 VOLT, but an additional 1 is vaguely recognizable. A rating other than 13A is unusual and would not comply to British Standard.

7, 8
View of connection unit after removing wall plate and cap. No. 7: The double pole switch in OFF position; no. 8 in ON position.
The switch can be put in ON position only after insertion of the fuse unit. The round slot has a plunger
(red arrow in image no. 3)* that blocks a metal strip. The fuse unit has a round pin. It lowers the plunger and releases the metal strip that now can be shift down when the knob of the switch is pulled to ON position (blue arrow in image no. 8).
It is very likely that at the same time the metal strip locks the round pin of the fuse unit, which means that the fuse unit can only be removed when the switch is in OFF position. The shape of the metal plate suggest the existence of such safety mechanism, but because the fuse unit is missing, verification is not possible.

When the double pole switch in ON position, L is connected to 'a' (see image no. 8). There is a fixed connection between 'a' and 'c'. The (missing) fuse makes, or breaks, the connection between 'c' and 'd' = L.I.  N is connected to 'b' = N.I.

* For constructional reasons the round slot and plunger are connected to earth. An earth terminal is needed only for connecting together the supply and load earth wires, or if the earth is provided by a metal conduit, connecting the load to the metal box via the screws. This was fairly common in UK metal-conduit installations, so the elaborate earthed metalwork of the device does not point specifically to the round hole being an earth contact. (info: Lucien Nunes).

Please contact me if you have a matching Britmac fuse unit on offer. You will find my address on the home page.


Logos of Ward & Goldstone and Volex
Ward & Goldstone Ltd was founded in 1892 by James Henry Ward and Meyer Hart Goldstone. They were active in electrical cables and accessories. The brand name Volex was already used in the 1910s for car batteries. Later they supplied complete electrical systems for cars. In the 1950s the company was also successful in producing appliance cords with moulded plugs.
In the early '80s Ward & Goldstone was in deep trouble. In 1983 new management changed the name to Volex Group. Finally, Volex electrical accessories became a part of Electrium. Since 2006 Electrium is a wholly owned subsidiary of Siemens Holding plc.

Main source: Grace's guide to British industrial history.


The Britmac trademark has been associated with a number of companies over the years. The first registration that could be traced dates back to 23 October 1931 by C.H. Parsons of Britannia Works in Tyseley, Birmingham 11.
In 1946 C.H. Parsons launched a subsidiary company called the Britmac Electrical Co. Ltd to handle sales of the accessories. The original Britmac logo is shown top right. The 'B' logo has been used later. The full name is used now.
In time Britmac became part of BICC, Dorman & Smith, hence Wylex, then Hanson and finally Electrium, which is now owned by Siemens AG UK.
Today Britmac focuses on BS 1363 underfloor track and floor boxes.

Information has been provided by Lucien Nunes.
Britmac logos


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