ISOMIL - Mineral Insulated Cables
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Components and Common Properties

The conductor or conductors are embedded in high density mineral powder which is hermetically sealed by a metal sheath. Dimensioning, namely the ratio of wall thickness, insulation layer thickness and conductor diameter, is of significance for the electrical and mechanical properties. Consequently, in the following we present cross-sections of a number of our standard cables as well as some of those made to customer specifications.

Standard Production

The more common cables have diameters between 0.5 and 10 mm. The choice of diameter is primarily determined by the requirements of the technical application in question.

The construction of several standard cables
of ISOMIL-T, -M cross sections.

Not all our stock can be supplied in maximum production lengths. When ordering please state the required minimum length, e.g. 1500 m in lengths not under 70 m.

Special orders are accepted in appropriate amounts. These special requests can be deviations from the standard production such as dimensions (sheath thickness, insulation thickness, conductor diameter), the number and design of the conductors, the material combination sheath / insulation / inner conductor or special electrical or other physical properties.

As a general rule, special orders are more involved and have as prerequisites a minimum production quantity; in some cases trial runs are required to clarify the position. Moreover the acquisition of materials which are not in stock must be considered.

Discussions with the customers prior to ordering are essential.

Examples of customer specials

Protection against the absorption of humidity

The insulation materials are so highly hygroscopic that the mineral powder when exposed through an open end can absorb so much moisture from the atmosphere in a few minutes that the insulation voltage conductor / conductor or conductor / sheath drops by several orders of magnitude.

Consequently, it is vital that the cable ends are kept hermetically sealed at all times, i.e. not only during production but also during further processing and usage. On dispatch both cable ends are moisture sealed with plastic, whereby the inner conductor/conductors are led out so that the insulation voltage can be checked at all times.

However, should moisture penetrate the cable in spite of all the preventive measures, it can be forced out by heating the cable end concerned e.g. with a flame, from the middle to the end. Experience shows that even in a cable which has lain open for several days the moisture does not penetrate more than 50 cm of the cable. It follows that if a cable end lies open over a shorter period then the penetration depth of the humidity is correspondingly less, e.g. a few cms. When drying out the reduction in humidity increases with rising temperature - at 450ºC suddenly (MgO). It follows that heating above 500ºC has no noteworthy advantages.

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