The Dutch HVAC Tag Dialect. NEN-EN-IEC 81346 Kenletters, Decoded

A kenletter is the class code inside a NEN-EN-IEC 81346 reference designation: one letter that says what class of object you are looking at. The classes are defined by purpose, so the letter tells you what the object exists to do, not what it is called in a catalogue. That is why a relay on a Dutch schema is K and not R. A relay receives a signal, acts on it, and passes it on, which puts it in the information-processing class, and that class carries K. The restricting class, R, holds resistors, non-return valves and balancing valves.

The other letters an engineer meets on a Dutch klimaat or regeltechniek sheet, in one line: B senses, M drives, Q switches or varies a flow of energy, W guides it through cable, pipe or duct, X connects, S is the thing a human presses, P is the thing a human reads.

This is a decode of that letter set as it is used on Dutch installation drawings, on an air-handling schema and on a CV heating sheet, with a worked breakdown of a tag string block by block.

What the standard actually fixes

NEN-EN-IEC 81346 is the Dutch adoption of IEC 81346, the international standard for structuring a technical system and naming its parts. Part 2 holds the class table. What the standard fixes is narrower than most readers expect, and a lot of the confusion around Dutch tags comes from expecting it to fix more:

• The aspect prefixes. = introduces the function aspect (what the object does in the system breakdown), + introduces the location aspect (where it physically sits), - introduces the product aspect (the physical object itself). See what is IEC 81346 for the aspect model in full.
• The class letter. The kenletter after the - comes from the class table in part 2, and subclasses refine it with a second letter.

What the standard does not fix is the project's own function and location codes. A function code for the air-handling installation, and a location code such as RK1 for the regelkast it is wired into, come from the coding manual the project issued. The standard governs the grammar. The project supplies the vocabulary.

The kenletter table

Seventeen letters are in use in the current edition. A, I and O are not used as class codes, and D, J, L, V, Y and Z are reserved.

The right-hand column is typical practice, not a rule from the standard. Classification follows purpose, and a project coding manual is entitled to argue a borderline object either way. A filter is the usual example: it treats the air, which reads as H, and it restricts the flow, which reads as R. Read the manual before you argue with the drafter.

The K question, settled

K and Q are the pair that catch people, so here they are side by side with their neighbours.

So the control cabinet of an air-handling unit reads as a chain: S (the operator presses), K (the logic decides), Q (the contactor closes), M (the motor turns), G (the fan moves air), B (the sensor reads the result), and back to K.

Worked decode: =AB2+RK1-K3

Read a Dutch reference designation from the prefixes inwards, not from left to right as a word. The codes below are illustrative.

Read as a sentence: the third information-processing object in control panel 1, serving air-handling installation AB2. If the schema shows a coil with a set of contacts beside it, that is your hulprelais.

Now note what the string does not say, because this is where an ISA-trained reader gets caught. It carries no measured variable and no loop number. -B1 on the same panel tells you an object senses something. It does not tell you whether the point lands on AI or on DI. A temperatuurvoeler and a vorstbeveiliging are both class B, and one is an analogue input while the other is a dry contact. The class narrows the signal class down. The function of the point decides it.

Drop the =, + and - to fit a spreadsheet column and you lose the only thing that made the designation unique. K3 exists in every panel on the site.

Worked decode: AB2-VB-04, the house convention

The second dialect on a Dutch set is not 81346 at all. On the mechanical and regeltechniek sheets you will often meet abbreviations built from Dutch words:

VB is neither a kenletter nor an ISA function code. It is an abbreviation of a Dutch noun. V carries no measured variable, and looking for one is the fastest way to misread a whole sheet. The abbreviation list sits on the drawing, in the legenda, and it is project-specific. When a set carries both dialects, and many do, the electrical schema is in 81346 designations while the climate sheets are in Dutch abbreviations, and the same physical damper appears once in each.

Dutch regeltechniek terms and their ISA and I/O equivalents

For an engineer reading a Dutch sheet with an ISA reflex, this is the translation that matters. The right-hand column is what the point becomes on the puntlijst.

The ISA column is the nearest equivalent, offered as a reading aid. It is a gloss, not a rename. A Dutch puntlijst keeps the codes the drawing prints, because the panel, the controller and the commissioning sheet all carry those codes and none of them will recognise a translated one. If the puntlijst itself is the job, regeltechniek puntlijst extraction covers what comes back: every point with its I/O class beside it, and the tag exactly as printed.

Three traps on a Dutch set

• Edition drift. A title block citing 61346 is common, and the class letters largely carried over, but the class table has been revised. Take the edition from the coding manual, not from habit.
• Numbering is local. Counts run per installation or per panel. K3 is unique inside +RK1 and nowhere else. Any register keyed on the product code alone will collapse objects that were never the same object.
• Two dialects, one building. The 81346 designation on the electrical schema and the Dutch abbreviation on the climate sheet can name the same damper. Cross-reference them once, in a controlled list, rather than renaming either in place.

Summary

The short version. A kenletter is the class code in a NEN-EN-IEC 81346 reference designation, and the classes are defined by purpose. K is information processing, which is why the hulprelais, the tijdrelais and the regelaar all carry it, while the contactor that switches the motor is Q and the protection device is F. Seventeen letters are in use: B, C, E, F, G, H, K, M, N, P, Q, R, S, T, U, W, X. A designation such as =AB2+RK1-K3 reads as function, then location, then object, and the class letter narrows the signal class without deciding it. On the mechanical sheets, expect Dutch house abbreviations such as VB for vorstbeveiliging instead, and take the meaning from the legenda.

Further reading

• ISA 5.1 vs IEC 81346, the same class system compared against the North American convention.
• What is IEC 81346, the aspect model and the object-class table.
• KKS vs IEC 81346, where the power-plant dialect sits against the same standard.
• AI, AO, DI, DO signal classes, where a Dutch point lands once it reaches the controller.