Triton (T3CDS) In Depth Application - Cold Flow

Introduction

Under IEC 60079 - 14 (latest edition) Clause 9.1.4 states that "The connection of cables and conduits to the electrical apparatus shall be made in accordance with the requirements of the relevant type of protection."

It then goes on to say that care should be taken when selecting a suitable cable entry device in conjunction with certain types of cable employing materials which can exhibit 'cold flow' characteristics. The standard states by way of example that "cable entry devices not employing compression seals which act upon part(s) of the cable having cold flow characteristics" should be employed.

There is a reason for this, which has long been recognised by most respected industry experts, but has not necessarily been widely published. That is to say that a standard compression seal, which differs from any of the CMP conceptual solutions, found in most other types of armoured cable glands uses only one action to tighten the armour lock and simultaneously apply the seal onto the inner cable sheath. This singular, uncontrolled action means that the seal is installed "blind" with a high probability of excess pressure exerted on the cable.

Ironically whilst this method of installation was used extensively in the past, and is still supplied by most manufacturers today, on assembly there is no way for the installer to identify the potential problem, although in the long term the consequences may be highly damaging.

It is our view, which is unlike those of our competitors who will continue to say one thing and do another, that the use of compression seals is the single biggest problem in the cable connection business today.

The latest standard also goes on to state that "Low smoke and/or fire-resistant cables usually exhibit cold flow characteristics", and that "Cold flow can be more fully described as thermoplastic materials which flow when subjected to pressure at ambient temperature."

With it's revolutionary concept of Cable Inner Sheath Sealing, the CMP TRITON CDS fully embraces the requirements of this latest standard and addresses a number of other fundamental compatibility and installation issues that have remained unanswered by most other cable gland manufacturers.

Getting to Grips with Soft Bedded Cable

The increasing popularity of flame retardant cables particularly for safety focussed application such as oil & gas installations, refineries and chemical plants has led to a proliferation of what are commonly described as soft bedded cables. A general description of a soft-bedded cable is one, which employs materials, which exhibit, 'significant cold flow' characteristics, ie thermoplastic materials, which flow when subject to pressure at ambient temperature.

Particular care should be taken when installing this type of cable in locations, where an explosive gas atmosphere may be present. For electrical equipment with type 'd' - explosion protection, it is usually necessary to form a gas seal on to the bedding of the cable. The relevant code of practice (IEC60079-14:2003) clearly states that compression seals shall not be employed in these circumstances. A common method of addressing this problem is to use a displacement seal, whereby the seal is displaced as the gland is tightened. The purpose of this design enables the user to control the level of displacement of the seal, ensuring a functional and more importantly, safe, seal is achieved without exerting undue pressure onto the cable.

Another consideration when using flexible soft bedded braided cables is the fact that the bedding will usually assume the shape of the metallic wire braid, which is laid in direct contact with it during manufacture of the cable.

After removal of the braid armour, this results in an uneven sealing surface because of the basket weave impression of the wire braid, which leaves a stepped rather gorge like surface with indentations in a linear and axial 'criss-cross' fashion. Consequently this raises questions over the effectiveness of other types of seal such as the diaphragm type in whether it can become effective in preventing gas migration, to mention just one concern.

Naturally, many factors influence the final method of installation including, environment, ambient temperatures, method of protection, and the specific construction of the cable being used. CMP Products are always willing to provide an expert assessment of a given application, drawing on many years experience of installation procedures, providing assurances that a safe solution is achieved every time.

Triton CDS, codename T3CDS, from CMP Products is the ideal answer for soft bedded cables or other situations where some cable gland solutions cause undue stress to the cable installations.