Side-by-side reference

Understand the difference.

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

First referenceCompare with

ICT

Symbols

Interposing current transformer

An interposing CT sits between a main CT and a relay or meter. It corrects ratio mismatch, provides phase-shift compensation for transformer differential schemes, or isolates circuits, and it was standard in electromechanical differential protection before relays could compensate internally.

Drawing use: Schematic / SLD
Application: Metering & protection
Reference family: IEC / Manufacturer

A distinction that matters

An interposing CT is an auxiliary in the secondary circuit; a main CT carries the primary circuit current.

Full reference

ΣCT

Symbols

Summation current transformer

A summation CT has several primary windings, each fed from the secondary of a main CT, and one secondary winding that carries their sum. It lets one meter or relay see the total current of several feeders, or in some relay designs combines three phase currents into a single weighted quantity.

Drawing use: Schematic / SLD
Application: Metering & protection
Reference family: IEC / Manufacturer

A distinction that matters

A summation CT adds currents before measurement; a summation energy meter adds energy after measurement.

Full reference

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