Skip to main content

Other Fluke companies:

Fluke Calibration Fluke Biomedical Fluke Networks Fluke Process Instruments
  • Accelix
  • Amprobe
  • Beha-Amprobe
  • Comark
  • Landauer
  • Pacific Laser Systems
  • Pomona
  • RaySafe
  • Schad
  • Pruftechnik

Select your country site

  • Africa and Middle East
    Africa
    ( English | Français )
    Middle East
    ( English )
  • Americas
    Argentina
    ( Español )
    Costa Rica
    ( Español )
    Mexico
    ( Español )
    Bolivia
    ( Español )
    Dominican Republic
    ( Español )
    Peru
    ( Español )
    Brazil
    ( Português )
    Ecuador
    ( Español )
    United States
    ( English | Español )
    Canada
    ( English | Français )
    El Salvador
    ( Español )
    Uruguay
    ( Español )
    Chile
    ( Español )
    Guatemala
    ( Español )
    Venezuela
    ( Español )
    Colombia
    ( Español )
  • Asia Pacific
    Australia
    ( English )
    Japan
    ( 日本 )
    South Korea
    ( 한국어 )
    China
    ( 中国 )
    Malaysia
    ( English )
    Taiwan
    ( Chinese Traditional )
    India
    ( English )
    Philippines
    ( English )
    Thailand
    ( English | ภาษาไทย )
    Indonesia
    ( English | Bahasa )
    Singapore
    ( English )
    Vietnam
    ( English | Tiếng Việt Vietnam )
  • Europe
    Austria
    ( Deutsch )
    Ireland
    ( English )
    Rest of Europe
    ( English )
    Belgium
    ( Français | Dutch )
    Italy
    ( Italiano )
    Spain
    ( Español )
    Czechia
    ( Czech )
    Netherlands
    ( Dutch )
    Sweden
    ( Swedish )
    Denmark
    ( Dansk )
    Norway
    ( Norsk )
    Switzerland
    ( Deutsch | Français )
    Finland
    ( Finish )
    Poland
    ( Polski )
    Turkey
    ( Türkçe )
    France
    ( Français )
    Portugal
    ( Português )
    United Kingdom
    ( English )
    Germany
    ( Deutsch )
  • Russia
    Russia
    ( Russian )

Select your country site

  • Africa and Middle East
    • Africa English
    • Africa Français
    • Middle East English
  • Americas
    • Argentina Español
    • Colombia Español
    • Bolivia Español
    • Brazil Português
    • Canada English
    • Canada Français
    • Chile Español
    • Costa Rica Español
    • Dominican Republic Español
    • Ecuador Español
    • El Salvador Español
    • Guatemala Español
    • Mexico Español
    • Peru Español
    • United States English
    • United States Español
    • Uruguay Español
    • Venezuela Español
  • Asia Pacific
    • Australia English
    • China 中国
    • India English
    • Indonesia English
    • Indonesia Bahasa
    • Japan 日本
    • Malaysia English
    • Philippines English
    • Singapore English
    • South Korea 한국어
    • Taiwan Chinese Traditional
    • Thailand English
    • Thailand ภาษาไทย
    • Vietnam English
    • Vietnam Tiếng Việt Vietnam
  • Europe
    • Austria Deutsch
    • Belgium Français
    • Belgium Dutch
    • Belgium Français
    • Belgium Dutch
    • Czechia Czech
    • Denmark Dansk
    • Finland Finish
    • France Français
    • Germany Deutsch
    • Ireland English
    • Italy Italiano
    • Netherlands Dutch
    • Norway Norsk
    • Poland Polski
    • Portugal Português
    • Rest of Europe English
    • Spain Español
    • Sweden Swedish
    • Switzerland Deutsch
    • Switzerland Français
    • Turkey Türkçe
    • United Kingdom English
  • Russia
    • Russia Russian
Fluke
  • Products
      • Accessories
        • See all
      • Building infrastructure
        • HVAC tools
        • Industrial Ethernet tools
        • Indoor air quality testing
        • Laser distance meters
        • Laser levels
        • Network cable testers
      • Calibration tools
        • Fluke Calibration
        • mA loop calibrators
        • Multifunction calibrators
        • Pressure calibrators
        • Temperature calibrators
      • Electrical tools
        • Basic electrical testers
        • Battery analyzers
        • Clamp meters
        • Digital multimeters
        • Earth ground
        • Installation testers
        • Insulation testers
        • Insulated tools
        • Portable appliance testers
        • Portable oscilloscopes
        • Power quality
      • Fluke software
        • Fluke Calibration software
        • Fluke SmartView
        • Fluke Networks software
      • Industrial imaging
        • See all
      • Intrinsically safe
        • See all
      • Mechanical maintenance
        • Laser alignment
        • Vibration analysis
      • Temperature measurement
        • Contact thermometers
        • IR thermometers
      • Thermal imaging
        • IR windows
        • Thermal cameras
        • Visual IR thermometers
      • Awards
      • New Fluke products
      • Test tools catalog
  • Learn
      • Best practices
        • Custody transfer
        • Electrical inspection
        • Energy efficiency
        • Equipment and production line testing
        • Fluid systems
        • Measurement basics
        • Motors and drives
        • Pressure calibration
        • Preventive maintenance
        • Safety
        • Temperature calibration
        • Test tools basics
      • Blog
      • Fluke education partnership program
      • Leak detector
      • Library
      • Online courses
      • Tools and calculators
        • Air leakage calculator
        • FOV calculator
      • Tradeshows and seminars
      • Webinars
  • Support
      • About us
        • Careers
        • Companies
        • Contact us
        • Corporate profile
        • Directions
        • Integrity
      • Calibration Services
      • Manuals
      • Press releases
      • Product registration
      • Repair
      • Return materials authorization
      • Safety notices
      • Service center locations
      • Software downloads
      • Warranties
  • Where to buy
      • Where to buy
      • Promotions and contests
Your privacy is important to us
Talk to
Sales

What is resistance?

Resistance is a measure of the opposition to current flow in an electrical circuit.

Resistance is measured in ohms, symbolized by the Greek letter omega (Ω). Ohms are named after Georg Simon Ohm (1784-1854), a German physicist who studied the relationship between voltage, current and resistance. He is credited for formulating Ohm's Law.

All materials resist current flow to some degree. They fall into one of two broad categories:

  • Conductors: Materials that offer very little resistance where electrons can move easily. Examples: silver, copper, gold and aluminum.
  • Insulators: Materials that present high resistance and restrict the flow of electrons. Examples: Rubber, paper, glass, wood and plastic.
Gold wire serves as an excellent conductor
Gold wire serves as an excellent conductor

Resistance measurements are normally taken to indicate the condition of a component or a circuit.

  • The higher the resistance, the lower the current flow. If abnormally high, one possible cause (among many) could be damaged conductors due to burning or corrosion. All conductors give off some degree of heat, so overheating is an issue often associated with resistance.
  • The lower the resistance, the higher the current flow. Possible causes: insulators damaged by moisture or overheating.

Many components, such as heating elements and resistors, have a fixed-resistance value. These values are often printed on the components' nameplates or in manuals for reference.

When a tolerance is indicated, the measured resistance value should be within the specified resistance range. Any significant change in a fixed-resistance value usually indicates a problem.

"Resistance" may sound negative, but in electricity it can be used beneficially.

Examples: Current must struggle to flow through the small coils of a toaster, enough to generate heat that browns bread. Old-style incandescent light bulbs force current to flow through filaments so thin that light is generated.

Resistance cannot be measured in an operating circuit. Accordingly, troubleshooting technicians often determine resistance by taking voltage and current measurements and applying Ohm's Law:

E = I x R

That is, volts = amps x ohms. R stands for resistance in this formula. If resistance is unknown, the formula can be converted to R = E/I (ohms = volts divided by amps).

Examples: In an electric heater circuit, as portrayed in the two illustrations below, resistance is determined by measuring circuit voltage and current, then applying Ohm's Law.

Example of normal circuit resistance
Example of normal circuit resistance
Example of increased circuit resistance
Example of increased circuit resistance

In the first example, total normal circuit resistance, a known reference value, is 60 Ω (240 ÷ 4 = 60 Ω). The 60 Ω resistance can help determine the condition of a circuit.

In the second example, if circuit current is 3 amps instead of 4, circuit resistance has increased from 60 Ω to 80 Ω (240 ÷ 3 = 80 Ω). The 20 Ω gain in total resistance could be caused by a loose or dirty connection or an open-coil section. Open-coil sections increase the total circuit resistance, which decreased current.

Reference: Digital Multimeter Principles by Glen A. Mazur, American Technical Publishers.

Recommended products

Fluke 3000 FC General Maintenance System
Fluke 3000 FC General Maintenance System
Fluke 87V Industrial Multimeter
Fluke 87V Industrial Multimeter
Fluke 179 True-RMS Digital Multimeter
Fluke 179 True-RMS Digital Multimeter
Fluke 289 True-RMS Data Logging Multimeter
Fluke 289 True-RMS Data Logging Multimeter
©2019 Fluke Corporation. Specifications subject to change without notice. 6004180

Products

  • Where to buy
  • Manuals
  • Product registration

Company

  • Careers
  • Companies
  • Integrity
  • Supplier handbook

Customer service

  • Contact us
  • Directions
  • Safety notices
Facebook YouTube Twitter LinkedIn Instagram
Fluke. Keeping your world up and running.®
  • Privacy policy
  • Fluke terms of use
  • Fluke terms and conditions of sale
  • Fluke terms and conditions of service
  • Feedback
  • Site map
©1995 - 2019 Fluke Corporation
    • Products
      • Accessories
        • See all
      • Building infrastructure
        • HVAC tools
        • Industrial Ethernet tools
        • Indoor air quality testing
        • Laser distance meters
        • Laser levels
        • Network cable testers
      • Calibration tools
        • Fluke Calibration
        • mA loop calibrators
        • Multifunction calibrators
        • Pressure calibrators
        • Temperature calibrators
      • Electrical tools
        • Basic electrical testers
        • Battery analyzers
        • Clamp meters
        • Digital multimeters
        • Earth ground
        • Installation testers
        • Insulation testers
        • Insulated tools
        • Portable appliance testers
        • Portable oscilloscopes
        • Power quality
      • Fluke software
        • Fluke Calibration software
        • Fluke SmartView
        • Fluke Networks software
      • Industrial imaging
        • See all
      • Intrinsically safe
        • See all
      • Mechanical maintenance
        • Laser alignment
        • Vibration analysis
      • Temperature measurement
        • Contact thermometers
        • IR thermometers
      • Thermal imaging
        • IR windows
        • Thermal cameras
        • Visual IR thermometers
      • Awards
      • New Fluke products
      • Test tools catalog
    • Learn
      • Best practices
        • Custody transfer
        • Electrical inspection
        • Energy efficiency
        • Equipment and production line testing
        • Fluid systems
        • Measurement basics
        • Motors and drives
        • Pressure calibration
        • Preventive maintenance
        • Safety
        • Temperature calibration
        • Test tools basics
      • Blog
      • Fluke education partnership program
      • Leak detector
      • Library
      • Online courses
      • Tools and calculators
        • Air leakage calculator
        • FOV calculator
      • Tradeshows and seminars
      • Webinars
    • Support
      • About us
        • Careers
        • Companies
        • Contact us
        • Corporate profile
        • Directions
        • Integrity
      • Calibration Services
      • Manuals
      • Press releases
      • Product registration
      • Repair
      • Return materials authorization
      • Safety notices
      • Service center locations
      • Software downloads
      • Warranties
    • Where to buy
      • Promotions and contests
    • Other Fluke companies
      • Fluke Calibration
      • Fluke Biomedical
      • Fluke Networks
      • Fluke Process Instruments
      • See more Fluke brands
        • Accelix
        • Amprobe
        • Beha-Amprobe
        • Comark
        • Emaint CMMS
        • Landauer
        • Pacific Laser Systems
        • Pomona
        • Pruftechnik
        • RaySafe
        • Schad