CABLE GLANDS
Introduction
In electricity and in instrumentation a cable gland is a component which allows an electric cable to pass through a partition, wall or bulkhead. It provides a seal against foreign matter, dust, water, etc., and mechanically locks the cable. It can consist of several elements, e.g.:
- A main part with dual thread forming a sleeve for the cable;
- A nut which fixes the body of the cable gland to the partition, associated if necessary with a seal,
- A pressure-deformable sleeve: formerly made of tow but now made of rubber or synthetic material and which provides the sealing;
- A nut which, either by deforming the end of the cable gland body, or using a cylindrical or tapered wedge, applies pressure to the deformable sleeve.
The cable passes through all the parts, in other words the cable gland is assembled by sliding the different elements onto the cable. A cable gland can be made of metal (usually brass), or synthetic material (plastic).
A metal cable gland can, where necessary, be used to earth the cable screen (triple effect cable gland).
It is important to use the right type of cable gland according to the protection zones defined by the ATEX 95 standard. The standard size of an instrumentation cable gland is M20 x 1.5.
It is important to ensure that the diameter of your cable gland correctly corresponds to your cable diameter because, on site, I once saw a large cable gland with a small cable and the whole assembly had been sprayed with silicone.
Procedure for electrically connecting a transmitter
Follow the instructions given below for wiring the transmitter:
- Remove the plastic protection blanks, from one or both the electrical connections present on the sides of the top part of the transmitter housing.
- Remove the cover from the housing on the connection side. For explosion-proof installations (certified Eex d), do not open the transmitter covers when the transmitter power supply voltage is present.
- If an output indicator is present, remove it by unclipping it. Apply a strong pressure to the whole of the indicator to prevent the cover from coming away from its base.
- Slide the cable into the cable gland and into the open access.
- Connect the positive conductor to the + terminal and the negative conductor to the terminal.
Tighten the cable gland and seal the electrical accesses. When the installation procedure is terminated, ensure that the electrical accesses are correctly sealed against the ingress of rain, gas or corrosive vapours.
Tighten the cable gland and seal the electrical accesses. When the installation procedure is terminated, ensure that the electrical accesses are correctly sealed against the ingress of rain, gas or corrosive vapours.
Screw up the housing cover by turning it until there is metal to metal contact between the cover and the transmitter housing. For explosion-proof installations EEx d or i, lock the cover by turning the locking screw.
And that is all!! Your transmitter is now wired according to good instrumentation practices.
CONNECTING A CABLE TO A COMPRESSION COUPLING
Mark the place where the cable armour must be cut.
Cut away the PVC sheath with a knife.
Expose (uncover) the armour.
Tie a piece of wire around the armour. Leave a space for the cable gland between the wire and the end of the PVC sheath.
Cut part of the way through the armour wire with a hacksaw.
If you cut all the way through the armour you may damage the inner core insulation.
Cut the armour wires with a hacksaw.
The wires must be cut evenly.
Take only four (4) or five (5) strands at any one time.
Cut back a little more of the outer sheath so enough of the armour is showing to cover the end of the clamping cone.
Now you can see the insulation around the inner core.
Place the gland locking nut and the compression ring
over the cable.
Twist the inner core against the lay of the steel wire armour. (depends on which end of the cable you are removing).
The steel wire will fan out.
Place the main body of the cable gland over the inner core.
Make sure the steel wire goes over the top of the gland.
Move the compression ring over the steel wire.
Make sure the wire is gripped between the compression ring and the gland.
Move the locking nut over the compression ring and tighten it on to the gland.
Remove the inner PVC sheath to expose the conductors.
Remove the insulation from the end of each conductor so the conductors can be terminated.
Mark the place where the cable armour must be cut
Remove the insulation from the end of each conductor so the conductors can be terminated.
Cut away the PVC sheath with a knife.
Expose (uncover) the armour.
Tie a piece of wire around the rmour.
Leave a space for the gland between the wire and the end of the PVC sheath.
Cut part way through the armour wire with a hacksaw.
If you cut all the way through the armour you may damage the inner core insulation.
Break off armour wires.
The wires must break off evenly.
Take only four (4) or five (5) strands at any one time.
Cut back a little more of the outer sheath so enough
of the armour is showing to cover the end of the
clamping cone.
Now you can see the insulation around the inner
core.
Place the gland locking nut and the compression ring
over the cable
Twist the inner core against the lay of the steel wire
armour. (Depends on which end off the cable you
are making off).
The steel wire will fan out.
Place the main body of the gland over the inner core.
Make sure the steel wire goes over the top of the
gland.
Move the compression ring over the steel wire.
Make sure the wire is gripped between the
compression ring and the gland.
Remove the inner PVC sheath to expose the
conductors
Remove the insulation from the end of each
conductor so the conductors can be terminated.
