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

PTC

Symbols

Thermistor motor protection relay

A thermistor protection relay is connected to a chain of PTC thermistors built into a motor's windings. When the windings reach the thermistors' rated response temperature, their resistance rises sharply and the relay opens its contact in the motor control circuit, protecting against overheating that a current-based overload cannot detect.

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

A distinction that matters

A thermistor relay measures winding temperature directly; a thermal overload relay models heating from current.

Full reference

OL NC

Symbols

Motor overload trip NC contact

An overload trip NC contact opens on the documented overload relay operation. It is commonly wired in the motor-control path while the overload sensing elements belong to the power circuit.

Drawing use: Schematic
Application: Control circuits
Reference family: IEC / Manufacturer

A distinction that matters

The auxiliary overload contact interrupts a control path; it does not itself carry the motor feeder current.

Full reference

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