Equipment labeling in electrical circuit diagrams

Table of contents

• 1. Introduction
• 2. Purpose of the equipment identification
• 3. Structure of the equipment identification
  • Sign
  • Concatenation
• 4. Placement of the BMK in circuit diagrams
• 5. Concatenation of identical BMK signs
• 6. Overview table of the BMK abbreviations
• 7. Conclusion

1. Introduction

In electrical engineering and automation technology, the equipment labeling (BMK) or reference labeling is an essential element for the unique identification of electrical components in circuit diagrams. It is used to systematically identify all equipment such as contactors, relays, motors or fuses and enables clear assignment within a system.

Without a standardized BMK, it would be difficult to understand circuit diagrams, diagnose faults or carry out maintenance work efficiently. Clear labeling reduces confusion, increases safety and facilitates cooperation between designers, technicians and service staff.

Equipment labeling follows international standards, in particular DIN EN 81346, which specifies a hierarchical system for the structured naming of equipment. This article explains the purpose of a BMK, how it is structured, where it should be placed and how a logical chain of markings is created. A final overview table shows the most important BMK abbreviations.

2. Purpose of the equipment identification

• Unique identification: Each item of equipment is given a unique identification to avoid confusion.
• Easier maintenance and troubleshooting: Technicians can identify components more quickly and rectify specific problems.
• Structured documentation: Standardized BMK increases the traceability of circuit diagrams.
• Improved communication: Standardized designations facilitate collaboration between different departments and external service providers.

3. Structure of the equipment identification

An equipment identifier consists of a sign followed by letters, numbers or letters followed by numbers, for example =A14.

Sign

The sign indicates the aspect according to which the object is identified, i.e. which property makes the object identifiable. The following aspects are possible:

• Identification by function, for example switching or signaling.
• Labeling according to location. This can be the installation location of a specific switch cabinet, for example.
• Identification by product, for example motors or indicator lights
• Labeling by type. This can be, for example, motors of the same series or with the same physical properties.

The following signs are used for the respective aspects:

Concatenation

In larger systems, identifiers are concatenated to make objects uniquely identifiable. The individual indicators are simply written one after the other.

For example, the BMK for a motor located in a control cabinet in a specific production plant could be =S3+U4-M3.

The letters from the table are used as code letters, while consecutive numbers are usually used for the numbers for clear identification. For example, -M1 and -M2 are both motors, but not the same motors.

Several variants for unique identification

4. Placement of the BMK in circuit diagrams

There are also clear specifications for the correct positioning of the reference mark on the component. These are defined in DIN EN 61082-1 (VDE 0040-1):

• If the circuit symbol has mainly vertical connection lines, the BMK must be placed to the left of the symbol
• If, on the other hand, the circuit symbol has mainly horizontal connection lines, the marking must be placed above the symbol.

The BMK should be aligned so that it can be read either horizontally or from the right-hand side.

Areas or holders for labels are often attached to the components themselves, on which the component can then be marked.

The correct position of the equipment marking

5. Concatenation of identical BMK signs

When concatenating reference indicators, it can happen that several partial indicators refer to the same type of aspect, for example to the function aspect.

In this case, the indicator can be designated in the following way:

However, the sign may only be omitted if the individual abbreviation begins with a letter and ends with a number. Thus =A1=G3=5 would not become =A1G35 but =A1G3=5.

6. Overview table of the BMK abbreviations

The letters A, I and O must not be used as identification letters.
The letters D, J, L, V, Y and Z are reserved for future standardization.

In some cases, objects can be assigned to several categories, in which case the BMK should be selected so that the main function of the object is best described. This includes circuit breakers that can both protect (F) and control (Q). In this case, the BMK should refer to the protective function.

7. Conclusion

Equipment labeling is an indispensable part of circuit diagrams. It ensures clarity, improves maintenance efficiency and facilitates the documentation of electrical systems. By complying with the standards, in particular DIN EN 81346, uniform and systematic labeling can be guaranteed. In the future, the digital management of BMK in CAD and CAE systems such as EPLAN will play an even more central role and further increase efficiency.