Tutorial: Mechanic - electrician Topic: Fundamentals of electrical engineering

the 2nd. year, RCD

Prepared by : Škarka Miloš

Projekt Anglicky v odborných předmětech, CZ.1.07/1.3.09/04.0002

je spolufinancován Evropským sociálním fondem a státním rozpočtem

České republiky.

Residual current device is an electrical device used for increased protection against injury caused by an electric current. It can‘t be used for basic protection – by automatic disconnection. Working wires are conducted through RCD, protective conductor mustn't be conducted through this device.It is used in environments with higher danger of injuries caused by an electric current.It‘s main parameters are:Nominal currentResidual (differential) current Selectivity

In normal conditions the vector sum of currents in working conductors equals null. In the secondary winding of the transformer no voltage is induced. In case of a current leak from the phase conductor to the ground, the voltage emerges in the secondary transformer winding, the current gets through the coil of the electro magnet and a malfunction is quickly disconnected from the rest of the electric network.

For one-phase circuits For three-phase circuits

Test buttons

(1) Input power terminals(2) Output load terminals(3) Reset button(4) Contacts (the second one is for relay)(5) Relay equipment

(6) Differential transformer(7) Control valve(8) Test button(9) Test conductor (orange)

RCD connection in TNC-S network

With null Without null

One-phase appliance

RCDs in TT, IT network

L1 L1 IT Network TT Network

Principle of RCD Which conductors have to be conducted

through RCD? What is a residual current? When do you have to use RCD? Draw the connection of RCD in TN network

What do numbers in picture 1 connote?

Picture 1

• http://www.jtlelektro.cz• www.wikipedia.cz