Definition for Circuit diagram and Common Wiring Scheme-I

Potential free contact, breaker contact, Definition for Raw power supply, LT & HT power supply, Auxiliary relays:

What is Potential Free Contact?

A two terminal device (NO or NC) should be a path of any circuits current flow in previously such a device contact is called Potential free contact or in simple words an isolated contact is called potential free contact. The contact should carry only our desired current or voltage. It should not mingle with other circuits auxiliary supplies.

What is the use or significance of potential free contact?

In control circuit, we use different types of auxiliary supplies. i.e electronics circuits needs only 24 Volts DC or 5 Volts DC (Direct Current) and breaker control circuit uses 110 VDC, AC Starter circuit use 230 Volts raw supply. Due to these various auxiliary supply, we cannot interface all the supply in to a single NO or NC’ s terminal so that we have to provide individual contacts for each circuits. These contacts are generally maintained by contactor multiplier circuits.

What is Breaker Contact?

Breaker contact is nothing but the feedback contact has taken from the breaker’s NO or NC. Such NO or NC is called Breaker Contact.


Note: NO means Normally Open and NC means Normally Close

What is Meant by Raw supply?

The 230 Volts alternating current supply is directly has taken from the distribution transformer without step down or step up action means such a power supply or source is called Raw Power supply.

Example: Single phase supply 230 Volts. 440 Volts two phase supply

Note: IF you get 230 Volts AC after installing 440V/230 Volts Transformer means, that can be considered as raw power supply.

What is LT and HT Power Supply?

Most two types of power supply are used in industry. One is Low tension and another one is high tension. Industry low tension power supply means 440 Volts and High tension power supply means the maximum voltage i.e if you use 11KV, then HT is 11KV. Also, HT and LT power supply cannot be taken from the same transformer. LT work as the alternative power source when the HT power supply failured. LT can be generated from DG set (Diesel engine set). LT provides Emergency power supply such as Turbine EOP (Emergency Oil Pump), Feed Water Pump, Barring Gear etc.

Auxiliary relays:

The relay which do not have over current element (current sensing coil) such a relays are called auxiliary relays. These relay do not contribute on power system protection and we can run the power system without of these relays. These relays are ensuring power system protection in systematic and they support main protection relays function.

Example: TCS (trip circuit super vision relays), Contact multiplier relay, Anti pumping relays, DC failure relays etc.

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