# ANSI/IEEE Insulation monitoring relay form Canonical URL: https://eloragrid.ai/symbols/ansi-insulation-monitoring-relay Publisher: Elora Grid Updated: 2026-10-28 Lookup label: IMD Drawing use: Schematic, SLD Reference families: IEEE / ANSI, Manufacturer ## Symbol convention Convention: IEEE / ANSI Form: Insulating Relay Autodesk IEEE Symbol Preview: Miscellaneous Relays, block HCR1F44. Matching functional counterpart linked separately. Independently drawn educational geometry; not a certified IEEE glyph or database identifier. Related representation: [Insulation monitoring relay](https://eloragrid.ai/symbols/insulation-monitoring-relay) IEEE-library form of 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 ANSI/IEEE Insulation monitoring relay form mean? This reference locates insulation monitoring relay in Autodesk's IEEE-oriented miscellaneous relays family. 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 public library uses HCR1F44 for its horizontal representation; this is a vendor block name, not an IEEE standards symbol number. ### A simple example Trace the measured quantity or initiating control signal separately from the output contacts. The device tag links the sensing or operating element to the controlled circuit; settings, reset behaviour and the actual terminal arrangement belong in the selected equipment documentation. ### What the drawings help you do 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. Check that only one monitor is active on each connected IT system. An insulation monitoring relay measures insulation resistance of an unearthed system; a residual current monitor measures leakage current in an earthed system. The linked functional counterpart explains the same operating role in its own drawing context; agreement of every detailed convention mark is not asserted. ### This particular reference IEEE-library form of insulation monitoring relay: 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. ### Terms - DC: Direct current: electricity flowing in one direction. - Normally open / normally closed: The contact state in the normal condition defined for the drawing. - Coil: A wound conductor that can produce a magnetic field when energised. Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram. - [Autodesk IEEE Symbol Preview: Miscellaneous Relays](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-DA549E3E-4ABB-426E-9331-0226EF55EAA7.htm) - [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/) ## What it represents This reference locates insulation monitoring relay in Autodesk's IEEE-oriented miscellaneous relays family. 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 public library uses HCR1F44 for its horizontal representation; this is a vendor block name, not an IEEE standards symbol number. Trace the measured quantity or initiating control signal separately from the output contacts. The device tag links the sensing or operating element to the controlled circuit; settings, reset behaviour and the actual terminal arrangement belong in the selected equipment documentation. 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. Check that only one monitor is active on each connected IT system. An insulation monitoring relay measures insulation resistance of an unearthed system; a residual current monitor measures leakage current in an earthed system. The linked functional counterpart explains the same operating role in its own drawing context; agreement of every detailed convention mark is not asserted. ## 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 ## Important distinction An insulation monitoring relay measures insulation resistance of an unearthed system; a residual current monitor measures leakage current in an earthed system. ## Facts - Convention evidence: Autodesk IEEE Symbol Preview: Miscellaneous Relays; published form: Insulating Relay. - Public vendor block: HCR1F44. Vendor library token, not an IEEE symbol number. - Measured quantity: Insulation resistance to earth - Preview: Independent educational concept; consult the publisher and applicable standard for the exact graphic - Artwork scope: Original educational geometry. Exact standard graphics, product ratings and terminal pinouts are not certified. ## Public references - [Autodesk IEEE Symbol Preview: Miscellaneous Relays](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-DA549E3E-4ABB-426E-9331-0226EF55EAA7.htm) — Autodesk. Public IEEE-oriented Miscellaneous Relays table explicitly lists HCR1F44 as Insulating Relay. This supports the vendor convention context, not reproduction of the publisher graphic. - [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/) — IEC. IEC context for graphical symbols used in diagrams; no IEC graphic is reproduced. ## Graphic scope Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.