Socket to 'em Charlie

Captain Charles Arnold was an electrical engineer who, in 1912, entered into a joint venture with his long-time friend Charles Reginald Belling. With an investment of £150 each, along with a third partner, Mr H E How, who soon dropped out, they formed Belling & Company to manufacture electric fires and other electrical appliances.

With the beginning of the war in 1914, Arnold sold his share of the company to Belling and joined the Royal Artillery – returning as a Captain with ideas for a new venture. Getting together with Belling again, the two formed The Heavy Current Electric Accessories Company, with a view to producing switches and sockets for the increasing number of appliances coming onto the market.

Very little flexibility
At the time, sockets were mostly thick gauge slotted brass tubes. The flexibility required for a firm contact came from the plug pins, which were split to allow a degree of compression on insertion. However, tolerances weren't as exacting as they are today and if the plug pins were on the small side they gave a loose fit with poor contact. If they were large, a great deal of force was required to insert and remove the plug.

Thin walled tubing had been introduced to try to solve this problem but, while providing the flexibility, these were very vulnerable to distortion by oversized or misaligned plug pins.

Arnold's alternative, known as the Multy Kontact spring grip socket outlet, also made use of thin gauge tubing. The difference was that the tubing had numerous flexible contacting tongues formed in its wall, while a complete ring of metal was left at the mouth of the socket to prevent distortion. The ring acted as a gauge and protected the tongues from excessive expansion on the basis that no pin larger than the maximum tolerance allowed by the British Engineering Standards Association (BESA) could be inserted.

Arnold also devised a new way of forming the contacting tongues. Instead of the tongues facing each other either side of a common slot, he used diametrically opposed banks of tongues by cutting two slots, one opposite the other.

The tongues were pressed inwards sufficiently that even a pin at the minimum BESA tolerance opened them as it was inserted. Each tongue was completely independent of the others and could even grip a pin mis-shapen by wear or faulty manufacture. This was the first socket to incorporate a gripping effect, rather than relying on the pin to do it.

It's possible that Arnold was inspired by nature in his design of the socket. In his provisional patent specification he described "a specially constructed socket arranged to give a maximum bearing or contact surface by means of numerous flexible spring tongues which actually grip the pin in much the same manner as the legs of two caterpillars on opposite sides of a flower stem".

The many points of contact built into the socket led Arnold to name it the Multy Kontact socket, from which MK eventually derived its name.

Marketed as 'the socket with a grip as firm and flexible as the hand', the Multy Kontact was not an immediate success. With Belling as a sleeping partner, Arnold rented a shop (gas-lit) in north London with a secondhand lathe and a drilling machine.

In these days when most properties still used gas, sales were slow and the company was on the brink of closure when the socket came to the attention of the Newcastle Electric Supply Company. They felt that the 'MK' socket was the best on the market and placed a large order, saving the company's bacon.

More orders followed but the big breakthrough came when BESA revised its standards to include the self-adjustment and contact-making standards of Arnold's design – so the MK socket became the standard.

Early MK sockets were made from hard-drawn brass tubing, then from brass rod or extruded sections and finally by pressing. MK took out 10 patents in developing pressed sockets for round and rectangular pins but in each case the solid ring or non-expandable entry was retained and remained so for many years.

By 1920 the range was expanding with the introduction of a two-pole connector designed for Belling's electric irons, followed by the Footpress switch that could be mounted on an electric fire and kicked on and off. The switch was made from metal and mica, rather than the conventional wood and ceramic, and was said to be virtually unbreakable.

Hardwood sockets
The following year a hardwood plug was added to the range, using bodies made from the walnut of ex-army rifles obtained from nearby Lee Enfield. At around this time the Multy Kontact socket and the Footpress switch were combined to make a switch socket.

In 1928, by which time the company was using a new insulating material called Bakelite, the company introduced the first ever shuttered socket. Described as 'anti-flash', the sockets incorporated automatic insulating caps that concealed and isolated the socket tubes as the plug was removed. This eliminated the arc of flame that was common when the plug was withdrawn.

In 1935 the design was simplified by the introduction of a simple spring loaded sliding insert 'butterfly' shutter, which exposed the current-carrying sockets on insertion of the plug's earth pin. With the launch of Logic, a rotary shutter was introduced that required the simultaneous insertion of both live and neutral pins to open, followed some years later, by a shutter that operates only when all three pins are inserted.

Insulating sleeves on the pins of plugs were introduced in 1964, initially with optional retractable insulating sleeves that became known as 'football shorts'. With the launch of Safetyplug in 1972, the sleeves were standard, though these did not become compulsory under British Standards until the mid-1980s.

In the early 1900s there was a great deal of unease about electricity amongst the general public. More accustomed to gas, some people even feared that the electricity would leak into the room if the socket was not switched off. The development of safe and reliable sockets through the innovations of engineers like Charles Arnold undoubtedly made a huge difference to the acceptability of electricity and the growth of the electrical industry.