What Is Resistance in a Circuit?
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What Is Resistance in a Circuit?
What is resistance in a circuit? It is the opposition to the flow of current. Fluke’s electrical reference defines it as “a measure of the opposition to the flow of current in an electrical circuit.” It is measured in ohms, symbolized by the Greek letter omega (Ω). This page explains the idea, the unit, and how resistance changes current, using only the sources we opened.
Quick answer
- Resistance opposes the flow of current.
- Its unit is the ohm (Ω).
- Higher resistance means lower current; lower resistance means higher current.
- Resistance is not measured in an operating circuit.
Resistance and current
Electrical current is the rate at which electrons flow past a point in a complete electrical circuit. Resistance limits that flow. Fluke’s page states the relationship directly: “The higher the resistance, the lower the current flow,” and “The lower the resistance, the higher the current flow.”
Why resistance matters in troubleshooting
Fluke describes two abnormal cases. If resistance is abnormally high, “one possible cause (among many) is damaged conductors due to burning or corrosion.” If resistance is abnormally low, “it could be due to insulators that were damaged by moisture or overheating.” The page adds that overheating is often associated with resistance problems.
How resistance is found
Resistance cannot be measured in an operating circuit. Fluke notes that troubleshooting technicians therefore often determine resistance by taking voltage and current measurements and applying Ohm’s Law. Ohm’s Law is “a formula used to calculate the relationship between voltage, current and resistance in an electrical circuit.” Rearranged, the same relationship is R = E/I (ohms = volts / amps).
Safety
Do not treat a resistance reading taken while a circuit is energized as valid. Fluke’s page says resistance cannot be measured in an operating circuit. Work on mains wiring can be lethal; panel and service work belongs to a licensed electrician.
How we chose
This explainer covers only the terms that the sources we opened define in their own text. We opened the pages listed under Sources on 2026-10-27 and used only passages on those pages. We left out related topics the sources do not cover, such as AC circuit analysis and component values.
What we could not verify
The sources we opened do not give resistance values for specific wire gauges, materials or components, so this article does not list any.
FAQ
What is the unit of resistance?
The ohm, symbolized by the Greek letter omega (Ω), according to Fluke.
Does more resistance mean more current?
No. Fluke states that “the higher the resistance, the lower the current flow,” and that “the lower the resistance, the higher the current flow.”
Can resistance be measured on a live circuit?
Fluke says resistance cannot be measured in an operating circuit. Technicians often determine it by taking voltage and current measurements and applying Ohm’s Law.
What can cause abnormally high resistance?
Fluke lists “damaged conductors due to burning or corrosion” as one possible cause, “among many.”
Sources
- Fluke Learn, “What is Resistance?” fluke.com/en-us/learn/blog/electrical/what-is-resistance (opened 2026-10-27)
- Fluke Learn, “What is Current?” fluke.com/en-us/learn/blog/electrical/what-is-current (opened 2026-10-27)
- Fluke Learn, “Ohm’s Law” fluke.com/en-us/learn/blog/electrical/ohms-law (opened 2026-10-27)
