IEC Reference Designations 

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The IEC publishes a series of documents and rules governing the preparation of documents, drawings and the referencing of equipment.   Depending on country and industry, people are either familiar with the IEC system or not.  For those not familiar it can be a little confusing at first.

Often when IEC document production is compared to other methods it is mistakenly assumed the difference is simply symbols.  This is not the case.  The IEC document and referencing system is a comprehensive approach covering symbols, drawing and layout techniques, equipment references, identification of terminals and signals, classification of documents and computer data organisation.   It also goes beyond just documentation and extends into physical devices and implementation. 

I've introduced IEC systems to three companies.  In each case my initial attempts were meet with criticism, objections and the belief that it was unduly complicating life.  However, in all these cases and after a couple of projects everyone on the team was highly praising of the IEC method and were not willing to go back to their old system.  In each case implementation of IEC based methods resulting in simplification of documents (drawings), better technical content on the documents, more consistency between documents and a reduction in the time to necessary produce the documents. 

One of the areas of the IEC system which is sometimes confuses the first time people come across it is the formulation of reference designations.  This note gives a brief overview and introduction to the reference designation system. 


In defining designations, prefix aspects are used:

Prefix Aspect
= Function - what does the product do
- Product  - (how is the object constructed
+ Location - where is the object located

The prefix is used to construct single level designations,
which shall consist of the following:

  • a letter code;
  • a letter code followed by a number
  • a number     

The IEC system allows drawing elements and products to be specified in either the functional, product or location aspect or some combination of two or more aspects.  Still sounds a little confusing?  Hopefully and example will make it easier to understand.

Application by Example

The IEC is fairly open on how you apply reference designations for projects and organisations.   Each project or organisation tends to be unique so this makes some sense.  For some recent projects we have used to following application of the reference designation system, which works has worked  reasonably well .  The approach is to ensure that the complete reference designation (tag number) for each item of equipment has a function part and a product part.  The location aspect is considered optional and only if required.  Some examples:

  • =N-A1  (switchboard)
  • =N-A1Q1 (circuit breaker)
  • =N-T1 (transformer)
  • =N-T1+L11 (transformer, located on level 11)

Function aspect [=]

For the function aspect, we use a variation of the principals set out in IEC 61346-2.  For example we use =N for a 400 V supply, if there are two independent feeds we may use =N1 and =N2, etc.

Code Definition Examples
H Installations for 30 kV ... <45 kV  
J Installations for 20 kV ... <30 kV  
K Installations for 10 kV ... <20 kV  
L Installations for 6 kV ... < 10 kV  
M Installations for 1 kV ... < 6 kV  
N Installations < 1 kV  
P Equipotential bonding Earthing protection
Lightning protection
V Storage of material goods Fuel Oil
X Auxiliary purpose outside main process

Alarm system, Clock system
Lighting installation
Electric power distribution
Fire protection system
Security system

Y Communication and information tasks Computer networks
Telephone system
Video surveillance system
Antenna System

Product Aspect [-]

Product aspect is in accordance with IEC 81346-2, code letters – see later in the note for a more detailed explanation.  Typical code letters include Q for circuit breakers, T for transformers, A for assemblies (switchboards), etc.  There are specified in more detail in IEC 60617 for each type of device.

Generally we number each product in a logical fashion which fits the project (i.e. -Q1, -Q2, -Q3, etc.).   For switchboards (Assemblies) we treat slightly different as shown in the table below.  This makes the reference designation more meaningful without over complicating the implementation.

Code Description
-A0xx Main Distribution Boards
-A1xxx Sub Main (MCCB) Distribution Boards
-A2xxx Motor Control Centres
A3xxx Local Motor Control Panel
-A4xxx not used
-A5xxx not used
-A6xxx Distribuion Boards (MCB)

"xxx'  represents an optional number. 

Initially we did tried to fix  'xxx' across projects to have some useful meaning.  This didn't work to well, so basically we allocate the numbers logically depending on the project and arrangement of systems. 

Location Aspect [+]

We leave the function aspect is freely definable.  Generally we find we do not need to use location as this tends to be obvious from the context of the document or drawings.  If we do need to use we would define logical set of locations for the project.  These may typically be things like +L23 (level 23),  +Z01 (zone 1) etc.


Reference Designation Example

IEC structuring is hierarchical in nature.  For example if switchboard =N-A1 contains a circuit breaker -Q1 then the full designation of the circuit breaker would be =N1-A1-Q1 (or more simply =N-A1Q1).   If the same circuit breaker contains a relay -K12, the full reference would be =N-A1Q1K12.  This is further illustrated in the image.   This feature of the system makes it easy to number everything uniquely and allows  for more commonality in the drawings. 

Project Examples

Some more example designations from a current project of ours:

  • =J03-Q0,  =J03-T1
  • =N1-A01, =N1-Q1, =N1-A614
  • =N1-A104W614
  • =N1-G1

IEC 81346-2 Classification of Objects

IEC 81346-2 "Industrial systems, installations and equipment and industrial products - Structuring principles and reference designations - Part 2: Classification of objects and codes for classes"

IEC 81346-2, published jointly by IEC and ISO defines classes and subclasses of objects based on a purpose- or task-related view of the objects, together with their associated letter codes to be used in reference designations. The classification is applicable for objects in all technical areas, e.g. electrical, mechanical and civil engineering as well as all branches of industry, e.g. energy, chemical industry, building technology, shipbuilding and marine technology, and can be used by all technical disciplines in any design process.

The Letter Codes

A letter codes enables classification of objects. The new letter codes, which are common to all technical branches, apply from IEC 81346-2 table 1.

There are in total 18 classes, identified by the following letter codes:

A - Two or more purposes or tasks

B -Converting an input variable into a signal for further processing

C - Storing of energy, information or material

E - Providing radiant or thermal energy

F - Direct protection from dangerous or unwanted conditions

G  -Initiating a flow of energy or material

H -Producing a new kind of material or product

K - Processing signals or information

M - Providing mechanical energy for driving purposes

P - Presenting information

Q - Controlled switching or varying a flow of energy, of signals or of material

R - Restricting or stabilizing motion or a flow of energy, information or material

S - Converting a manual operation into a signal for further processing

T - Conversion of energy maintaining the kind of energy

U - Keeping objects in a defined position

V - Processing (treating) of material or products

W - Guiding or transporting from one place to another

X - Connecting objects


    The above is a very brief introduction to the IEC reference designation system.  It is not an easy subject to cover briefly and is better understood by working with the system and seeing live examples.  When applied to projects, it does  fall into context and everything starts to make sense. 

    IEC Related Standards

    • Designation
      • IEC 81346: Structuring principles and reference designations
      • IEC 61175: Designation of signals
      • IEC 61666: Identification o terminals within a system
    • Symbols
      • IEC 60617: Graphical symbols for diagrams - maintained as a database
      • ISO 81714: Design of graphical symbols
      • ISO 14617: Graphical symbols for diagrams
    • Documentation Rules
      • IEC 61355: Classification and designation for documents
      • IEC 62023: Structuring of technical information and documentation
      • IEC 82045: Document management
    • Preparation of Documents
      • IEC 60848: Preparation of sequential function charts
      • IEC 61082: Proportion of documents used in electrotechnology - key  document for drawings
      • IEC 62027: Preparation of part lists
      • IEC 62079: Preparation of instructions
    • Data Organisation
      • IEC 82045: Meta data
      • IEC 61360 Data element types
      • ISO 10303: Step data model

    Steven McFadyen's avatar Steven McFadyen

    Steven has over twenty five years experience working on some of the largest construction projects. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. About the author

    myElectrical Engineering

    comments powered by Disqus

    1. Clive Lee's avatar Clive Lee says:
      5/8/2012 7:50 PM

      As a large company we are looking at implementing the DCC code as a part of the referance designation system. Reviewing the internet in 2012 there does not appear to be very much ativity in this field. Three years on from your article what is the industrial base using this standard?

      • Steven's avatar Steven says:
        5/9/2012 7:40 AM

        Clive, thanks for the comment.

        On the DCC (Document Classification Code), like you I have not seen it used too much. Given free choice I do implement it on the projects I am involved in – however, more often than not the client has their own numbering system we need to follow. I also run into issues with other disciplines not wanting to follow the system. A pity really as I do think the DCC is well thought out.

        Realizing we don’t have anything about DCC on the site, I added an article to the Notes section.

      • Clive Lee's avatar Clive Lee says:
        5/9/2012 7:26 PM

        My own research reveals that the power generating industry in Germany has adapted the reference designation system to the extent that they are in transition from KKS to RDS-PP. Further it is noted that DCC is applied in ISO 16952 which is a related standard for technical product documentation.

        For machinery and solution providers the standard for Safety of Machines - electrical equipment makes the recommendation of applying DCC (IEC-61355). This industrial branch is typified by small and medium sized companies where access to standards and insight into its use and correct applications probably involves resources in excess of their budget. In a competitive environment the reference designation with document classification should give a competitive edge where machines are to combined in process units and plants.

      • Steven's avatar Steven says:
        5/10/2012 6:28 AM

        Thanks for sharing your research.
        Hopefully this discussion will encourage a few people to have a look at the IEC 61355 DCC.

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