# Ohmmeter

Canonical URL: https://eloragrid.ai/symbols/ohmmeter
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: Ω
Drawing use: Schematic
Reference families: IEC, IEEE / ANSI

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.

### Terms

- 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.

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.

- [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/)
- [IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams](https://standards.ieee.org/ieee/315/515/)


## 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

## Important distinction

An ohmmeter measures ordinary resistance at low voltage; an insulation resistance meter applies a high test voltage to measure megohms.

## Facts

- Measured quantity: Resistance
- Source: Internal measuring supply
- Preview: Independent educational concept; consult the applicable standard and project legend for the exact graphic

## Public references

- [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.
- [IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams](https://standards.ieee.org/ieee/315/515/) — IEEE Standards Association. Graphic-symbol standards context for instrument letter designations.

## 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.