Multimeters are essential tools for diagnosing electrical issues in both domestic and commercial environments. Whether you're investigating a non-functional socket, flickering lights, or tripping breakers, a multimeter can help pinpoint the fault accurately.
At RCD Electrical, we use professional-grade multimeters daily to ensure safe and precise electrical diagnostics. In this article, we’ll walk you through the correct use of a multimeter, how it works, and what tests it performs to detect faults. We also highlight the safety precautions that must be followed every time.
What is a Multimeter?
A multimeter is a handheld electrical testing instrument used to measure:
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Voltage (V) – The potential difference between two points
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Current (A) – The flow of electric charge
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Resistance (Ω) – How much a component resists current
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Continuity – Whether a complete path for current exists
Most modern multimeters are digital (DMMs), providing clear and precise readings on an LCD screen. At RCD Electrical, we use calibrated and insulated devices for maximum accuracy and safety.
Step 1: Safety First
Before using any test equipment, always follow these essential safety checks:
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Isolate the power if testing for continuity or resistance.
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Use insulated gloves if working near live parts.
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Ensure the multimeter is set to the correct mode—incorrect settings can damage the meter or give false readings.
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Test the multimeter on a known source (e.g. a working socket) to confirm it’s functioning properly.
At RCD Electrical, safety is our top priority, and every diagnosis starts with risk control.
Step 2: Testing for Voltage
Voltage testing is crucial for checking if power is present and identifying overloads or under-voltage issues.
How to test AC voltage:
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Set the dial to the AC voltage symbol (V~).
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Insert the black lead into the COM port and the red lead into the VΩ port.
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Touch the probes to live and neutral terminals or live and earth.
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A typical UK mains supply should read around 230V.
If the reading is too high or too low, it may indicate a supply issue, damaged component, or incorrect load.
Step 3: Testing Continuity
Continuity testing checks whether an electrical path is complete. This is ideal for:
To test continuity:
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Set the dial to the continuity symbol (a diode or soundwave icon).
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Make sure power is off.
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Touch both leads to either end of the component or wire.
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A beep or reading close to zero ohms confirms continuity.
If there's no beep or infinite resistance, the circuit is broken or the wire is faulty.
Step 4: Measuring Resistance
Resistance testing helps identify degraded components or faulty wiring.
To measure resistance:
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Set the dial to Ω (ohms).
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Ensure the power is off.
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Touch the probes across the resistor or wire.
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Compare the reading to the expected value.
High resistance can indicate corrosion, loose connections, or internal breaks. RCD Electrical often uses this method when inspecting heaters, thermostats, or light fixtures.
Step 5: Measuring Current
Measuring current is more complex and typically done in series, meaning the multimeter becomes part of the circuit.
To measure current:
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Set the dial to A (amperes) and choose the correct range.
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Insert the red probe into the A port, not the V port.
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Break the circuit and place the probes so current flows through the meter.
Important: Incorrect use here can damage the multimeter or create a hazard. That’s why RCD Electrical handles this step with special caution, especially in high-current environments.
Common Faults Diagnosed with a Multimeter
Here are just a few faults our engineers regularly diagnose using multimeters:
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No power in a socket: Test for 230V AC, confirm continuity to the breaker
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Tripping RCDs: Check insulation resistance (with other tools), then check voltage and continuity of suspect appliances
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Blown fuses or switches: Use continuity testing
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Dim or flickering lights: Measure voltage under load and check for loose neutrals
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Damaged extension leads: Confirm continuity and resistance across each pin
The multimeter is not a one-size-fits-all tool—but in skilled hands, it’s one of the most powerful instruments available.
Why Choose RCD Electrical?
At RCD Electrical, our engineers are fully trained in the correct and safe use of multimeters and other diagnostic tools. We never guess—we measure, and then we fix.
Every diagnosis is followed by a clear explanation and a full report, with optional repair work carried out to the highest standard.
Need expert fault diagnosis? Call 02034882928
Email us at info@rcdelectrician.co.uk