How to Test a Consumer Unit
Last updated: 7 September 2026
Press the test button on the RCD, check MCB operation, and verify wiring with a multimeter.
Overview
Testing your consumer unit ensures your electrical system is safe. This guide covers testing RCDs, MCBs, and wiring.
Step-by-Step Fix
Before beginning any repair, ensure you have isolated power or water supplies. Clear your workspace, gather standard hand tools, and wear appropriate personal protective equipment (PPE).
- First, ensure you have the correct testing equipment: a multimeter, a non-contact voltage tester, and an RCD tester if available. Always follow safety procedures when working with electrical systems.
- To test an RCD, press the test button on the unit. It should trip immediately, cutting power to the circuit. Reset the RCD by pushing the switch back to the ON position.
- To test an MCB, switch it off and then back on. It should operate smoothly without sticking. If it fails to reset or trips immediately, it may be faulty.
- To test wiring, use a multimeter set to continuity to check for continuity between the line, neutral, and earth conductors. There should be continuity only where expected.
- If any tests fail or you are unsure about the results, contact a qualified electrician. Do not attempt to repair a consumer unit yourself.
- Check the tightness of all connections in the consumer unit. Loose connections can cause overheating and arcing, which can lead to fire.
- Check the condition of the consumer unit itself. If the unit is old or damaged, it may need to be replaced.
- After testing, ensure the consumer unit is securely closed and that all covers are properly fitted.
Common Symptoms & Diagnostic Resolutions
Review the common error codes and operating symptoms below to quickly identify the root cause of the fault before ordering replacement parts.
| Symptom / Code | Likely Root Cause | Recommended Resolution |
|---|---|---|
| RCD not tripping | Faulty RCD | Replace the RCD. This is a safety-critical component and must be replaced immediately by a qualified electrician. |
| MCB will not reset | Faulty MCB or circuit fault | Check circuit and replace MCB. If the circuit trips again immediately, there is a fault in the wiring that requires investigation by an electrician. |
| High resistance reading | Poor connection or damaged cable | Check all connections and tighten any that are loose. If the resistance remains high, the cable may be damaged and need replacing. |
| No continuity | Open circuit in wiring | Find and repair the break in the circuit. This may require tracing the cable and locating the fault, which is often at a connection point. |
Frequently Asked Questions
How often should I test my consumer unit?
RCDs should be tested quarterly using the test button. Full testing of the consumer unit and wiring should be done every 10 years or when a property changes hands. This is recommended by the IET Wiring Regulations (BS 7671).
Can I test my consumer unit myself?
You can press the RCD test button yourself, but comprehensive testing requires specialist equipment and knowledge. It is recommended to have a qualified electrician carry out full testing of your consumer unit and wiring.
What is the difference between an RCD and an MCB?
An RCD (Residual Current Device) protects against electric shock by detecting earth leakage. An MCB (Miniature Circuit Breaker) protects against overcurrent and short circuits. Modern consumer units often use RCBOs, which combine both functions.
How much does it cost to test a consumer unit?
The cost of testing a consumer unit varies depending on the size of the installation and the complexity of the work. On average, you can expect to pay between £100 and £250 for a full electrical inspection and test (EICR).