KKS vs IEC 81346. Two Ways to Identify a Power Plant.

KKS and IEC 81346 both answer the same question, "what is this object and where does it belong," but they come from different places and read differently on the page. KKS grew up inside the power industry and is everywhere on the existing fleet. IEC 81346 is the general, cross-sector reference designation standard, and its power-plant application, RDS-PP, is the system replacing KKS on new work. If you work across power projects you will meet all three, so it helps to see them side by side.

KKS in one paragraph

KKS, the Kraftwerk-Kennzeichensystem, is a power-plant identification system that names an object by where it sits in the plant breakdown and what function it performs. A KKS code reads as blocks: a function key that says which system and sub-system the object belongs to, then a component code that says what the object is, then a signal or point suffix. There are no aspect prefix signs; the structure is carried in the sequence and the letter and number blocks themselves. It has been the default across German-influenced power engineering for decades and is deeply embedded in existing plant documentation. For the full block-by-block breakdown, see KKS coding explained.

IEC 81346 in one paragraph

IEC 81346 is the international standard for structuring any technical system and assigning reference designations to its parts. It names an object through up to three independent aspects: what it does (the function aspect, prefix =), where it is (the location aspect, prefix +), and what it physically is (the product aspect, prefix -), with the object class taken from a single letter defined in IEC 81346-2. Because the aspects are independent, the same object can be described through whichever lens a given document cares about. It is not power-specific; it applies equally to buildings, infrastructure, and process plants. See what is IEC 81346 for the aspect model in full.

A direct comparison

Where RDS-PP fits (the bridge)

The confusing part is that these are not two competing systems but a lineage. RDS-PP, the Reference Designation System for Power Plants, is VGB's successor to KKS, and it is built on IEC 81346. So RDS-PP is what you get when you take the general 81346 aspect model and apply it specifically to power generation, carrying forward the domain knowledge that KKS encoded. A team moving off KKS is almost always moving to RDS-PP, not to bare IEC 81346, and the aspect prefix signs are the visible tell that a drawing has made that move.

Which one you will meet, and when

• An existing plant, built before the last decade: almost certainly KKS, throughout the documentation.
• A new-build or a major retrofit under a European-influenced contractor: increasingly RDS-PP, so IEC 81346 aspect signs on the tags.
• A cross-border or mixed-vendor project: possibly both, on different document sets, which is where the cross-referencing work lives.

Reading a drawing that mixes them

When a project carries both, the failure mode is trying to normalize one into the other in place. Do not. Hold one register as the master, map the other to it, and keep the mapping as its own controlled document. The two systems encode different things in different orders, so a lossy in-place rename loses information that someone downstream will need. Tags extract and reconcile far more reliably when each system stays in its own form and the relationship between them is explicit.

Further reading

• KKS coding explained, the block-by-block KKS reference.
• What is IEC 81346, including the object-class kenletter table.
• ISA 5.1 vs IEC 81346, the same comparison against the North American standard.