Understand the difference.

Compare the meaning, drawing context and source references of two entries. A similar graphic or shared abbreviation does not establish equivalence.

K

Symbols

Neutral-current measuring relay

This relay form is used where a CT is installed in a neutral conductor or in the earthing connection of a transformer or generator star point. Current there indicates earth faults or, in four-wire systems, heavy unbalance and triplen harmonic loading, depending on where the CT sits.

Drawing use

Schematic / SLD

Application

Metering & protection

Reference family

IEC / Manufacturer

A distinction that matters

A neutral-current relay measures one neutral path; a residual connection sums the three phase CTs to derive the same quantity.

Full referenceAdd to legend

CT RES

Symbols

Residual connection of phase CTs

A residual CT connection combines secondary currents from phase CTs to obtain a residual-current input. This is a connection arrangement that should be drawn explicitly rather than assigned an unsupported separate standard-symbol number.

Drawing use

SLD / Schematic

Application

Metering & protection

Reference family

IEC / Manufacturer

A distinction that matters

Residual connection of three phase CTs is not the same physical sensor as a core-balance CT.

Full referenceAdd to legend

Original educational previews. Follow the source references on each full entry for the appropriate standard or selected product.