Understand the difference.

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

IDMT

Symbols

Inverse-time characteristic qualifier

The inverse-time qualifier marks a measuring element whose operating time depends on how far the measured quantity exceeds the setting: the larger the overcurrent, the faster the trip. On drawings it appears with overcurrent and earth-fault elements that are graded against fuses and downstream relays.

Drawing use

Schematic / SLD

Application

Metering & protection

Reference family

IEC

A distinction that matters

An inverse-time qualifier marks a current-dependent delay; a definite-time qualifier marks a fixed delay.

Full referenceAdd to legend

t

Symbols

Definite-time delay qualifier for measuring relays

This qualifier is added inside or beside a measuring relay box to show that the relay operates a fixed time after its measured quantity crosses the threshold. Combined with a quantity such as I> or U<, it tells the reader the element is definite-time rather than instantaneous or inverse-time.

Drawing use

Schematic / SLD

Application

Metering & protection

Reference family

IEC

A distinction that matters

A definite-time qualifier gives a fixed delay; an inverse-time qualifier gives a delay that shortens as the quantity increases.

Full referenceAdd to legend

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