Rules for reading electrical circuits and drawings

The main technical documents for an electrician and electrician are drawings and electrical diagrams. The drawing includes the dimensions, shape, material and composition of the electrical installation. It is not always possible to understand the functional relationship between elements. It helps to understand the electrical circuit that you must have when using wiring diagrams.

I'm reading electrical circuits, you need to know and remember well: the most common symbols for coils, contacts, transformers, motors, rectifiers, lamps, etc. for example, motors, rectifiers, incandescent and gas-discharge lighting fixtures, etc., the properties of series and parallel connections of contacts, coils, resistances, inductances and capacitors.

Breaking chains into simple chains

Each electrical installation meets certain operating conditions.Therefore, when reading the diagrams, firstly, it is necessary to identify these conditions, secondly, to determine whether the obtained conditions correspond to the tasks that the electrical installation must solve, and thirdly, it is necessary to check whether there are «unnecessary» conditions found themselves on the way and evaluated their effects.

Several techniques are used to solve these problems.

The first is that the Circuit Diagram is mentally divided into simple circuits, which are first considered separately and then in combinations.

A simple circuit includes a current source (battery, secondary winding of a transformer, charged capacitor, etc.), a current receiver (motor, resistor, lamp, relay coil, discharged capacitor, etc.), a straight wire (from a current source to the receiver ), return wire (from sink to source) and one device contact (switch, relay, etc.). It is clear that in circuits that do not allow opening, for example, circuits of current transformers, there are no contacts.

When reading a circuit, you must first mentally break it down into simple circuits to check the capabilities of each element, and then consider their joint action.

Reality of circuit solutions

Installers are aware that the schemes can not always be implemented in practice, although they do not contain obvious errors. In other words, design wiring diagrams are not always real.

Therefore, one of the tasks when reading electrical diagrams is to check whether the specified conditions can be met.

The unreality of circuit solutions usually has the following reasons:

• there is not enough power to operate the device,

• "extra" energy enters the circuit, causing unexpected operation or preventing timely release electrical appliances,

• there is not enough time to perform the specified actions,

• the machine has set a set point that cannot be reached,

• co-applied devices with markedly different properties,

• switching capacity, insulation level of devices and wiring are not taken into account, switching surges are not extinguished,

• the conditions under which the electrical installation will operate are not taken into account,

• when an electrical installation is designed, its operating state is taken as a basis, but the question of how to bring this state and in what state it will be, for example, as a result of a short-term power failure, is not resolved.

The order of reading electrical diagrams and drawings

First of all, you need to familiarize yourself with the available drawings (or compile content if there is none) and organize the drawings (if this is not done in the project) according to their purpose.

The drawings alternate in such an order that the reading of each subsequent one is a natural continuation of the reading of the previous one. Then they understand the adopted system of designations and markings.

If it is not reflected in the drawings, it is clarified and recorded.

On the selected drawing, they read all the inscriptions, starting with the seal, then notes, notes, explanations, specifications, etc. When they read the explication, they must find on the drawings the devices listed in it. When they read the specifications, they compare them with the explanations.

If the drawing contains links to other drawings, then you must find those drawings and understand the contents of the links.For example, a circuit includes a contact belonging to the apparatus shown in another diagram. This means that you need to understand what kind of apparatus it is, what it is for, under what conditions it works, etc.

When reading drawings that reflect power, electrical protection, control, alarm, etc.:

1) determine the power supplies, the type of current, the magnitude of the voltage, etc. If there are multiple sources or multiple voltages applied, then they figure out what caused it,

2) divide the scheme into simple values ​​and, taking into account their combination, establish the conditions of action. We always start by considering the device we are interested in in this case. For example, if the engine does not work, then you need to find its scheme on the diagram and see which contacts of which devices are included in it. Then they find the device circuits that control those contacts, etc.

3) construction of interaction diagrams, with their help establishing: the sequence of work in time, the sequence of the time of operation of the devices within the given device, the sequence of the time of operation of jointly working devices (for example, automation, protection, telemechanics , controlled drives, etc.), the consequences of a power failure. To do this, one by one, assuming that the switches and power supplies are off (fuses blown), they assess the possible consequences, the possibility of the device entering a working position from any state it could be in, for example after an audit,

4) evaluate the consequences of possible malfunctions: non-closure of contacts one by one, insulation failures relative to ground sequentially for each object,

5) violation of the insulation between the conductors of overhead lines extending outside the premises, etc.,

5) check the circuit for the absence of false circuits,

6) evaluates the reliability of the power supply and the operating mode of the equipment,

7) checks the implementation of measures to ensure safety, subject to the organization of work provided for in these rules (PUE, SNiP, etc.).