MΩ
Insulation resistance meter
Indicating instrument applying a high DC test voltage to read insulation resistance in megohms.
Schematic
Symbols · Ω
Ohmmeter
Indicating instrument for electrical resistance, shown as an instrument circle marked with the ohm sign.
In plain English
What does Ohmmeter mean?
An ohmmeter indicates resistance by passing a small current from its own source and measuring the result. On permanent drawings it appears in test equipment, earthing test points and some machine monitoring panels, while on schematics for test procedures it shows where resistance is to be measured.
A simple example
Because the instrument supplies its own measuring current, it must only be connected to not supplied with operating power circuits unless it is specifically designed otherwise. The symbol does not tell you the measuring voltage, range or whether a two-wire or four-wire connection is used.
What the drawings help you do
Confirm the measured circuit is not supplied with operating power. Check for four-wire connection when low resistances are measured. An ohmmeter measures ordinary resistance at low voltage; an insulation resistance meter applies a high test voltage to measure megohms.
This particular reference
Indicating instrument for electrical resistance, shown as an instrument circle marked with the ohm sign. An ohmmeter measures ordinary resistance at low voltage; an insulation resistance meter applies a high test voltage to measure megohms.
- Terminal
- An identified point where a conductor connects.
- Rating
- A value stating the conditions for which equipment is specified.
- Schematic
- A drawing showing function and connections rather than physical appearance.
Read the source: IEC graphical symbols for diagrams · IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams
Schematic · Ω
What it represents
An ohmmeter indicates resistance by passing a small current from its own source and measuring the result. On permanent drawings it appears in test equipment, earthing test points and some machine monitoring panels, while on schematics for test procedures it shows where resistance is to be measured.
Because the instrument supplies its own measuring current, it must only be connected to de-energised circuits unless it is specifically designed otherwise. The symbol does not tell you the measuring voltage, range or whether a two-wire or four-wire connection is used.
How to read it
- Confirm the measured circuit is de-energised.
- Check for four-wire connection when low resistances are measured.
Information to show or reference
- State range
- Show test connections
- Note isolation requirements
A distinction that matters
An ohmmeter measures ordinary resistance at low voltage; an insulation resistance meter applies a high test voltage to measure megohms.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
IEC graphical symbols for diagrams
IEC context for graphical symbols used in diagrams; no IEC graphic is reproduced.
IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams
Graphic-symbol standards context for instrument letter designations.
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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