Wiring reference designator

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A reference designator unambiguously identifies a component in an electrical schematic or on a printed circuit board. The reference designator usually consists of one or two letters followed by a number, e.g. R13, C1002. The number is sometimes followed by a letter, indicating that components are grouped or matched with each other, e.g. R17A, R17B.

There are several references available, but there is no specific worldwide standard.

This document also covers the recommended cable dimension for 3 phase motors.

In this document we present the EuSurplus standard where all new machine build will use as much as possible the recommendations described here.

Nominal current in 3 phase motors

Short circuit nominal current in asyncronous motors with 4 poles (reference Schneider Electric)

Power Kw HP 220V 230V 380V 400V
0.37 0.5 1.8 2 1.03 0.98
0.55 0.75 2.75 2.8 1.6 1.5
0.75 1 3.5 3.6 2 1.9
1.1 1.5 4.4 5.2 2.6 2.5
1.5 2 6.1 6.8 3.5 3.4
2.2 3 8.7 9.6 5 4.8
3 - 11.5 - 6.6 6.3
- 5 - 15.2 - -
4 - 14.5 - 8.5 8.1
5.5 7.5 20 22 11.5 11
7.5 10 27 28 15.5 14.8
9 - 32 - 18.5 18.1
11 15 39 42 22 21
15 20 52 54 30 28.5
18.5 25 64 68 37 35

Cable size and colors

Single cables (multicore)

Description Color Size mm^2 Comment
IO _____ Gray 1mm^2 Suitable for A < 1
5VDC _____ Red 1mm^2 Suitable for A < 1
12VDC _____ Yellow 1mm^2 Suitable for A < 1
24VDC _____ White 1mm^2 Suitable for A < 1
Phase L _____ Brown - Amperage dependable
Neutral N _____ Blue - Amperage dependable
Ground PE _____ _____ Yellow + Green - Amperage dependable

Power cable

IEC 60446 standard AC power

Description Color Size mm^2 Comment
Phase L1 _____ Brown - Amperage dependable
Phase L2 _____ Black - Amperage dependable
Phase L3 _____ Gray - Amperage dependable
Neutral _____ Blue - Amperage dependable

Motor connection cable

IEC 60446 standard AC power

Description Color Size mm^2 Comment
U _____ Brown - Amperage dependable
V _____ Black - Amperage dependable
W _____ Gray - Amperage dependable

Reference designator

Most of this information was obtained from Wikipedia and http://softelectro.ru/

To indicate an element type are encoded in Latin capitals

The first letter in the mandatory and defines the element type, the second letter breaks the type of items for a subset.



Reference Description
AT Attenuator


Converters from non electric to electrical devices or the inverse (except generators and power supplies)

Reference Description
BA Speaker
BB magnetostrictive element
BC selsyn sensor
BE selsyn receiver
BF Phone (capsule)
BK Heat Sensor
BL Photocell
BM Microphone
BP pressure sensor
BQ piezo
BR speed sensor (tachogenerator)
BS Pickup
BV speed sensor



Reference Description
C Capacitor
CN Capacitor network


Micro circuits

Reference Description
D Diode (including zener, thyristors and LED)
DA Scheme of the integrated analog
DB Bridge rectifier
DD Integrated circuits, digital, logic element
DS Display
DT Delay device


Miscellaneous elements

Reference Description
EK Heating element
EL Lamp lighting
ET Squib
EMI EMI filter


Fuses, protective devices

Reference Description
FA Discrete element of protection using instantaneous current
FB Ferrite bead
FD Fiducial
FP Discrete element of protection using current inertia
FU Fuse
FV Discrete element protection voltage, discharger


Generators, power

Reference Description
GB Battery


Indicator devices and signal

Reference Description
HA Alarm
HG LED digit
HL Light signaling device




Reference Description
J Jack connector (female)
JP Link (Jumper)


Relays, contactors, starters

Reference Description
KA Current switch
KH Pointing relays
KK Electrothermal relays
KM Contactor, magnetic starter
KO Overload relay
KSS Solid state relay
KT Relay
KV Voltage relay


Inductors, chokes

Reference Description
L Inductor
LL Choke fluorescent lighting


Reference Description
M Motor




Measuring equipment (mostly)

Reference Description
P Plug connector (male)
PR Resolver
PS Power supply
PT Clock (time counter)
PV Voltmeter
PW Wattmeter
PC Pulse counter, encoder incremental or absolute


Switches and circuit breakers to power circuits (power supply, power equipment, etc.)

Reference Description
QF Circuit breaker
QK Shorting
QS Disconnector



Reference Description
R Resistors
RK Thermistor
RP Potentiometer
RU Varistor


Switching devices in control circuits, alarm and measurement. Note. Designation SF used for devices that do not have contacts of power circuits

Reference Description
SA Switch
SB Button switch
SP Pressure switch
SQ Position switch
SK Temperature switch



Reference Description
TV Voltage transformer





Reference Description
YA Electromagnet
YB Electromagnet brake
YA Electromagnet chuck or plate


Terminal device filters. Terminators

Reference Description
ZL Limiter
ZQ Quartz filter