Tutorial: Mechanic - electrician

Topic: Basics of electrical engineering the 2nd. year Basic characteristics of electric appliances

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.

Appliance classes are determined by the way of providing protection against dangerous contact in case of a malfunction of a device. Possible ways of connection are determined according to usage of an appliance (immovable or movable). Only such conductors can be connected to an appliance (L, N, PE) corresponding to clamps on an appliance. If there is an additional appliance adjustment carried out, it has to be visibly marked on connection spots (for example the discarding of the PE clamp, while using the protection by the nonconductive environment). Movable appliances are meant for moving (carrying). If such an appliance isn‘t meant to be hold in hand, it mustn't be moved (carried) while switched on.

Appliances have a working insulation and are equipped with a protection clamp or a protective contact. These are: washing machine, oven, iron, computer, ...

Protection class II. Appliances have double or reinforced insulation and don‘t have (mustn‘t have) a protection clamp. Their whole surface is made of insulating material or they can have some parts made of metal, but always insulated with the reinforced insulation. These are: Shaver, hairdryer, power drill, grinder...

Protection class III. Appliances are connected to low voltage, so to SELV and PELV networks: These are: Low-volt bulbs, low-volt electric gardening, healthcare or agriculture appliances...

Class of a device

device marking or manuals

Conditions for device connection to an installation

Protection class 0

Use only in the non-conductive environment

or protected by the electric separation

electric separation carried out individually for each device

Protection class 1

Protective clamp markingor by letters PE or by the color combination green-yellow

Connection of this clamp to the protective installation connection

Protection class 2

Marking by sign not relying on any protective installation measures

Protection class 3

Marking by sign connection only to SELV or PELV networks

The protection against the dangerous contact via reset. The conductor PE(PEN) is connected to the conductive casing of the device. Animate parts are separated from the casing by the working insulation. We control the transitional resistance and the insulation state at this device.

Immovable appliance connected in the TN-S network.

Immovable appliance connected in the TN-C network.

Movable appliance for connecting into the socket.

Three-phaseThree-phase One-phase

Protection against dangerous contact via double insulation. Surface of an appliance should be made of an insulant. Potential metal parts have to be separated from animate parts in a way equal to the double insulation (plastic gears, pulling bars etc.). This insulation barrier mustn't be violated in any regular device malfunction (for example during short circuit in the motor winding there can be no casing melting). These devices have this mark on the surface:

The immovable appliance connected in the TN-S network. This appliance mustn‘t be connected to the PE conductor.

The immovable appliance connected in the TN-C network. If the appliance have the N clamp, it is connected to the PE conductor via conductor with a blue insulation color.

Movable appliance connected to the plug. Line has to be permanently attached to the device. There mustn‘t be a clamp for connecting the PE conductor at the plug. Allowed combination of colors of the line is blue – black (brown) and black – brown. The line can‘t have the green-yellow color vein.

Basic protection: voltage reducing; Protection in case of a malfunction: the separation from other circuits;

Protection construction elements: powered by the source of low voltage by the SELV or PELV source separating the appliance from the network;

Type of protection sign: picture no. 3 on the label

Powering winding: two-vein;

Connecting plug: two-pole, designed impossible to connect into the 230 V/50 Hz network.

The appliance of the third class is recognizable by the atypical connecting plug of the network circuit. Even here it is needed to verify this assumption by checking the type sign.

The voltage source can be a battery, a safety transformer, but not an autotransformer (there is no galvanic separation)

Appliance division into classes according to the protection

What is in the picture no. 1 What is in the picture no. 2

picture 1 picture 2

How many veins does the line for connection of the class I appliance have?

How many veins does the line for connection of the class II appliance have?

Why an autotransformer can‘t be used as a source to SELV?

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