In an electrical diagram for each symbol is associated with a Tag (name) which will identify the device within the set of drawings, other documents associated with the system and the device itself once it is installed in the field. There are many ways to choose the tag, and depends on the designer, two ways are frequently used will be explained.
Way 1: The tag for the symbol consists of two parts, the class and the number. For example the initials in Q3, Q refers to a protection switch and numeral 3 is used to distinguish if there are several protections. Often it combine more than one letter for the class, for example the letter K refers to a relay or a contactor (starter) if combined with the letter M then KM refers to the contactor (starter) of a motor. According to the standard IEC750 the tag must begin with a hyphen, for example -Q3A.
Way 2: The tag for the symbol consists of three parts: drawing number, class and location in the drawing. For example 1Q15 refers to a protection switch located in the plane 1 band 15 (the drawings are often divided into bands or squares to help find elements). In a variant of this, the location in the drawing is changed by consecutive numbers, for example if there are two protection switches in drawing No. 1; their tags would be 1Q1 and 1Q2.
Below is the table for letters that are used in class.
Class. Tag.
|
Letra |
Tipo de aparato | Ejemplo |
|
A |
Assemblies, subassemblies. | Amplifier using discrete components, magnetic amplifier, laser, maser, printed circuit board |
|
B |
Transducers, from nonelectrical to electrical quantity or vice versa | Thermoelectric sensor, thermo cell, photoelectric cell, dynamometer, crystal transducer, microphone, pickup, loudspeaker, synchro, resolver |
|
C |
Capacitors | |
|
D |
Binary elements, delay devices, storage devices | Digital integrated circuits and devices, delay line, bistable element, monostable element, core storage, register, magnetic tape recorder, disk recorder |
|
E |
Miscellaneous | Lighting device, heating device, device not specified elsewhere in this table |
|
F |
Protective devices | Fuse, over-voltage discharge device, arrester |
|
G |
Generators, power supplies | Rotating generator, rotating frequency converter, battery, oscillator, quartz-oscillator |
|
H |
Signalling devices | Optical indicator, acoustical indicator |
|
J |
— | — |
|
K |
Relays, contactors | |
|
L |
Inductors, reactors | Induction coil, line trap, reactors (shunt and series) |
|
M |
Motors. | — |
|
N |
Analogue elements | Operational amplifier, hybrid analogue/digital device |
|
P |
Measuring equipment, testing equipment | Indicating, recording and integrating measuring devices, signal generator, clock |
|
Q |
Switching devices for power circuits | Circuit breaker, disconnector |
|
R |
Resistors | |
|
S |
Switching devices forcontrol circuits, selectors | Control switch, push-button, limit switch, selectorswitch, dial contac |
|
T |
Transformers | |
|
U |
Modulators, changers | Discriminator, demodulator, frequency changer, coder, inverter, converter |
|
V |
Tubes, Semi-conductors | Diode, transistor, thyristor |
|
W |
Transmission paths,waveguides, aerials | Conductor, cable, busbar, waveguide |
|
X |
Terminals, plugs, sockets | Connecting plug and socket clip, test jack, terminal board, soldering terminal strip, link, cable sealing end and joint |
|
Y |
Electrically operated mechanical devices | Brake, clutch, pneumatic valve |
|
Z |
Terminations, hybrid transformers, filters, equalizers, limiters | Crystal filter, network |
