The electrical connector 1s rapidly becoming a critical component in Subsea Control Systems. In recent years the advent of the Fluid Filled connector, in all it various guises, has greatly improved the reliability of the device and allowed its use in more and more critical applications.

This paper seeks to provide an insight into the connector, its design, development, testing and implementation in a number of applications and also to explain the functioning of one particular type.

A brief history of the evolution of the subsea electrical connector In general is also provided along with descriptions of three variations of the basic fluid-filled principle and termination methods.

The paper also calls for continued industry involvement in the further progression of the product.


The use of electrical equipment subsea is now an essential factor in both Commercial and Military activities. The earliest "diving boats", dating back to Robert Fulton's NAUTILUS of 1798, were obviously purely mechanical devices having only two hull penetrations, namely those for propulsion and steering.

The earliest use of electrics subsea appears to have been in 1881 when the first practical electrically driven submarine was developed by the French engineer GOUBET.

In these early vehicles however, sea water and electricity were kept strictly apart and no hull penetrations for cables were required. This changed In 1908 when a submarine equipped with telephone and lights was produced, again by a Frenchman, Abbe Raoul. The penetrations here were most likely simple stuffing glands which could give no protection in the event of cable damage.

By far the greatest impetus to any technological development is given by the onset of war, but, whilst the submarine itself was extensively developed during the First World War, the greatest leap forward in underwater instrumentation came during the Second with the introduction of Sonar ("ASDIC") systems and sophisticated listening equipment such as Hydrophones.

These detection systems could obviously be used In static applications as well as on submarines and then deployment in defensive roles necessitated the development of cable and penetration systems suitable for long term immersion in very hostile conditions.

The need for reliable underwater electrical systems was obviously now a high priority.


The simplest method of penetrating the wall of a pressure vessel is by stuffing gland. This is suitable only for modest pressures and, because of extrusion, not for extended periods. Most significantly however, particularly for manned vessels, no protection against water ingress through a damaged cable is provided. Thus the severing of a cable, a not infrequent event. In the early days, would almost certainly result in a flooded vessel.

The initial solution to this problem came with the development of the Water Blocked Penetrator. This device very effectively prevented water ingress through damaged cables but was unable to prevent the loss of electrical integrity of all circuits even in the event of only one being damaged.

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