Q021702
Insulation-failure indication
An insulation-failure indication identifies the documented insulation-related failure condition.
IEC
Symbols · IMD
Insulation monitoring relay
Relay that continuously checks insulation resistance of an unearthed (IT) system to earth and alarms on a first fault.
In plain English
What does Insulation monitoring relay mean?
An insulation monitoring relay is connected between the conductors of an unearthed (IT) system and earth, and injects a measuring signal to determine insulation resistance. It warns when insulation falls below its setting so a first fault can be located before a second fault causes a trip.
A simple example
The symbol shows the device and its connections but not the measuring method, which matters on systems with drives or large DC components. Only one insulation monitor should normally be active on a galvanically connected system, so the drawing should show any disconnection or interlock between parallel systems.
What the drawings help you do
Check that only one monitor is active on each connected IT system. Identify alarm outputs and test button wiring. An insulation monitoring relay measures insulation resistance of an unearthed system; a residual current monitor measures leakage current in an earthed system.
This particular reference
Relay that continuously checks insulation resistance of an unearthed (IT) system to earth and alarms on a first fault. An insulation monitoring relay measures insulation resistance of an unearthed system; a residual current monitor measures leakage current in an earthed system.
- DC
- Direct current: electricity flowing in one direction.
- Coil
- A wound conductor that can produce a magnetic field when energised.
- Terminal
- An identified point where a conductor connects.
Read the source: AutoCAD Electrical: Miscellaneous monitoring relays · IEC graphical symbols for diagrams
Schematic / SLD · IMD
What it represents
An insulation monitoring relay is connected between the conductors of an unearthed (IT) system and earth, and injects a measuring signal to determine insulation resistance. It warns when insulation falls below its setting so a first fault can be located before a second fault causes a trip.
The symbol shows the device and its connections but not the measuring method, which matters on systems with drives or large DC components. Only one insulation monitor should normally be active on a galvanically connected system, so the drawing should show any disconnection or interlock between parallel systems.
How to read it
- Check that only one monitor is active on each connected IT system.
- Identify alarm outputs and test button wiring.
Information to show or reference
- Show system and earth connections
- State alarm thresholds
- Reference interlock between parallel monitors
A distinction that matters
An insulation monitoring relay measures insulation resistance of an unearthed system; a residual current monitor measures leakage current in an earthed system.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
AutoCAD Electrical: Miscellaneous monitoring relays
Public AutoCAD Electrical relay listing that names the Insulating Relay block; the illustration is independently drawn.
IEC graphical symbols for diagrams
IEC context for graphical symbols used in diagrams; no IEC graphic is reproduced.
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. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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