Understand the difference.

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

MRB

Symbols

Motor restart-inhibit block

Suppresses an automatic restart under the documented post-trip or supply-return condition. A motor feeder combines switching, motor protection and an operating command. Starting permission, running feedback and protection trip are different signals even where one relay or controller processes all of them.

Drawing use

Schematic

Application

Control circuits

Reference family

Manufacturer

A distinction that matters

Restart permission must follow the operating philosophy. This reference describes the named application; it does not establish a new IEC graphical symbol, an ANSI device-function number or an exact manufacturer connection diagram.

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KM

Symbols

Contactor

A contactor uses an operating mechanism to switch its main contacts and may include auxiliary contacts for control or indication. On a power drawing it represents the main switching path; on a schematic its coil and contacts may be distributed and connected by identifiers.

Drawing use

SLD / Schematic

Application

Control circuits

Reference family

IEC / IEEE / ANSI

A distinction that matters

A contactor and circuit breaker have different duties. Adding an overload relay does not make every contactor assembly equivalent to a circuit breaker.

Full referenceAdd to legend

Follow the full entry for source drawings and the appropriate standard or selected product. Equipment previews show a manufacturer drawing where available, otherwise a 3D thumbnail.