Armoured Cable Glands
Why Do We Use Cable Glands?
A cable gland (or as sometimes called; a cable fitting) is a mechanical device used to securely attach the end of a cable to an instrument, junction box, or piece of equipment. Cable glands provide many functions:
- To firmly secure cable entering a piece of equipment
- To maintain the ingress protection of the piece of equipment (minimum of IP54 for 'e' and 'n' type enclosures. Where the enclosure wall thickness is less than 6mm a sealing washer or thread sealant will be required to maintain IP54 protection)
- To maintain earth continuity between a piece of equipment and any armouring in the cable
- To ensure containment of an internal explosion in flameproof equipment
- To provide strain relief for the cable.
Is There a British Standard for Cable Glands?
The Code of Practice for selection, installation and inspection of cable glands used in electrical installations is covered in BS 6121-5 1989 Mechanical cable glands.
Selecting Cable Glands
Items to consider when selecting a cable gland for a particular installation include:
- Possibility of electrolytic action between the gland and the enclosure. Shortened lifetime for the glands and the cable entries can result if incompatible materials are selected. The most common materials used are brass, stainless steel and plastic. Material choice will influence cost.
- Degree of Ingress Protection required. See our page on IP ratings.
- Certification of gland for use in Hazardous areas
- Normal or barrier gland required
- Size of cable being terminated
- Size of cable entry on piece of equipment
- Thread form on the piece of equipment. The most common thread forms in use are imperial threads (NPT), metric threads, and PG threads.
What is a Barrier Gland?
Barrier glands are similar to normal glands, except a compound sealant material is used to ensure the inside of the cable is gas tight as well as the outside.
When Should a Barrier Gland be Used?
BS EN60079-14 Electrical Apparatus for Explosive Gas Atmospheres Part 14 - Electrical Installations in Hazardous Areas (other than Mines) provides a selection process for deciding if a barrier gland is required. There are various options to consider, however if the hazardous gas require IIC apparatus, or if the volume of the enclosure is greater than 2 litres then it is likely you will need to use a barrier gland. IIC apparatus is generally associated with Hydrogen.
Gable Gland Sizing
Cable gland size tables are provided below for general guidance, however reference should be made to the relevant British Standard or gland supplier.
Metric Thread Example: If your instrument, or cable enclosure has a metric thread then using the chart below you can see that if you have a cable with 4 cores, with a nominal area of 4mm2 then an M20 cable-gland should be used.
PG Thread Example: If your cable entry has a PG11 thread form (PG is from the German Panzergewinde) then from the gland sizing chart below, a cable with a maximum diameter of 10mm, and minimum of 5mm can be used.