Cable Terminations

High Voltage Cables are protected by many layers such as the insulation, armouring, shielding, etc.  When the cable is to be terminated at a busbar or at an equipment, the insulating and protective layers around it are removed.  This leaves the conductor exposed and there is a risk of flash overs and arcing at these spots.

Hence, cables need to be properly terminated to provide electrical and mechanical protection to the conductors at the point of connection.

There are different types of cable terminations such as straight through joints, cold shrinkable types, Heat shrinkable types, etc.  Cable joints need to be flexible, have good mechanical strength and chemical and thermal stability.

Cable Termination have frills to increase tracking resistance.

Electrical Contact Cleaner

Electrical Contact Cleaners are used for cleaning electrical contacts in panels, motors and other fittings. 

The contact cleaner consists of a cleaner such as isopropyl alcohol contained in a spray-container.  The Electrical Contact Cleaner can remove impurities such as oil, grease, etc.  The jet of air is used to remove deposits.

Contact Cleaners using Carbon Tetra Chloride  were widely used until a few years back.  However, today, contact cleaners no longer use Carbon Tetra Chloride as it is considered to be detrimental to the ozone layer. 

Remotely operated MCBs

Remote Operated MCBs are MCBs which have a provision for remote operation.  Conventional MCBs are used to trip the circuit in the event of an overcurrent.  They are not,however, sensitive to variations in voltage. 

The remote operated MCBs can be connected to a voltage monitoring relay which can trip the MCB in the event of an overvoltage or an undervoltage.  This can be ideal for equipment which are voltage-sensitive.

Remote operated MCBs can also be used in applications where it is practically difficult to operate the MCBs.  An example would be a motor which is located at a height along with the MCB. 

The remote operated MCBs also permit the remote resetting of the MCB.  MCBs of equipments which are located at a distance can be reset remotely from the control room. 

Ordinary MCBs can be fitted with actuators which trip them in response to a remote command.

Illuminated Switches

Illuminated Switches are used to indicate the position of the switch or the condition of a circuit.  Illuminated switches find wide application in control panel and switching equipment.  The illuminated switch consists of a lamp which is placed inside the switch.  The lamp is powered on or off from an external circuit. 

Illuminated switches were made of filament lamps, however, now they are being increasingly made from LEDs. 

The switches can be fitted with one or more contacts.  Illuminated switches are available both as push buttons as well as well as buttons with latch facility. 

Switches are usually maintenance free.  A periodic cleaning of the contacts with a contact cleaner would be sufficient.

The Yoke in a DC machine

The function of a Yoke in a DC machine is twofold.  The yoke acts as path for the magnetic flux.  It also provides mechanical support and shape to the dc machine.

As it is a path for the magnetic flux, the yoke should be made only of a magnetic material. 

The Yoke is usually made of cast iron, forged steel or cast steel.  In certain large machines, the yoke is made of two pieces which are bolted together.

PVC Insulation

PVC is a material which is widely used for insulating cables, busbars and wires.  Thermal and chemical Stability and flexibility have made PVC the insulation of choice for many applications.  They have smaller bending radius.    PVC insulation is used for cables operating at up to 70 degrees C.

Special heat resistant PVC can with stand temperature upto 90 degree C.  The plastic strength of PVC can be increased by the addition of plasticizers.

Another advantage of PVC is the ease of making joints when connecting two cables. 

PVC insulation tapes are also widely used.