Q021211
Mechanical interlock between devices
A mechanical interlock indication links devices whose movements are constrained by a physical relationship.
IEC
Functional block · TTP
Trapped-key transfer permissive
Functional block · Switchgear
An independently authored application reference. The drawing shows the named function or circuit relationship; use the project legend and selected equipment documentation for its drafting form and connections.
Browse this installation focusIn plain English
What this block does
Represents the required transfer of a key between equipment to enforce an operating dependency.
A simple example
In a switchgear feeder panel, a control diagram can prevent an incompatible combination of breaker, disconnector and earthing-switch positions. The physical equipment documents determine which restrictions are mechanically enforced. For this reference, the drawing identifies “Key availability” at the input and “Dependent operation permission” at the output. Key sequence and electrical state are different evidence.
What the drawings help you do
Start at the named input: Key availability. Identify its source device or document and the state represented on the drawing. Follow the named output: Dependent operation permission. Cross-reference its destination and separate the command from confirmation that the equipment responded.
- Input
- Key availability
- Output
- Dependent operation permission
- Application reference
- An explanation of a named drawing function or circuit relationship; the project documents define the equipment and its connections.
Read the source: Masterclad medium-voltage switchgear: circuit-breaker section interlocks
Schematic · TTP
What it represents
Represents the required transfer of a key between equipment to enforce an operating dependency. An interlocking function permits or blocks an operation according to the positions and conditions of related equipment. Electrical, mechanical and trapped-key interlocks implement different parts of a coordinated operating philosophy.
In a switchgear feeder panel, a control diagram can prevent an incompatible combination of breaker, disconnector and earthing-switch positions. The physical equipment documents determine which restrictions are mechanically enforced. For this reference, the drawing identifies “Key availability” at the input and “Dependent operation permission” at the output. Key sequence and electrical state are different evidence.
Identify each initiating position, the action being blocked and the consequence of missing feedback. An illustrative logic diagram must not be treated as an operating procedure or proof of a complete safety system. The functional block is an independent explanation of this named application. Equipment-specific ratings, terminal connections and operating conditions must be established in the project documentation.
How to read it
- Start at the named input: Key availability. Identify its source device or document and the state represented on the drawing.
- Follow the named output: Dependent operation permission. Cross-reference its destination and separate the command from confirmation that the equipment responded.
- Key sequence and electrical state are different evidence.
- Identify each initiating position, the action being blocked and the consequence of missing feedback. An illustrative logic diagram must not be treated as an operating procedure or proof of a complete safety system.
Information to show or reference
- Label the source and connection reference for key availability.
- Identify the destination and defined state of dependent operation permission.
- Record the equipment or control-document revision supporting this functional block.
- Check this application limit in the project design: Key sequence and electrical state are different evidence.
A distinction that matters
Key sequence and electrical state are different evidence. 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.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Masterclad medium-voltage switchgear: circuit-breaker section interlocks
Public technical context for switchgear interlocking functions. Breaker control, mechanism, position contacts, racking interlocks and test interfaces. The application text and educational graphic are independently authored; the publisher does not certify this representation.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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