What is this?
A randomly tripping switch is one of the most frustrating electrical faults because there is no clear pattern to help with diagnosis. The trip could be an MCB, RCD, or RCBO. Random tripping often points to an intermittent fault — one that comes and goes depending on temperature, vibration, moisture, or load conditions. These faults are often harder to diagnose but should not be ignored.
Common causes
- Loose connection that only faults when the cable expands with heat or contracts with cold
- Intermittent appliance fault that occurs only at certain points in its cycle
- Degraded cable insulation that creates earth leakage under certain conditions
- Cumulative leakage from multiple appliances reaching the RCD threshold at unpredictable times
- Faulty or ageing protective device that is becoming oversensitive
- Vibration from nearby traffic or building work causing a loose connection to fault intermittently
Is it dangerous?
Random tripping is not an immediate emergency, but intermittent faults can be more dangerous than permanent ones. A loose connection that arcs intermittently is a fire risk. The unpredictability also means the fault could become permanent at any time, leaving you without power.
Can I fix it myself?
Keep a detailed log of every time the trip switch goes off: date, time, weather conditions, what appliances were running, and what you were doing. This log is invaluable for an electrician. Note which switch trips — MCB, RCD, or both. Try to identify any correlation, even a loose one.
When to call an electrician
Call an electrician when the frequency of tripping is causing inconvenience or concern. The longer you leave an intermittent fault, the harder it may become to diagnose if it worsens into a permanent fault. Bring your log of trip events when the electrician visits.
What will an electrician do?
Review your log of trip events to look for patterns
Inspect the consumer unit for loose connections and signs of overheating
Test all circuits with insulation resistance testing, looking for borderline readings
Check the trip switch itself for correct operation and sensitivity
Test suspect appliances with portable appliance testing
Install data logging equipment if the fault cannot be reproduced during the visit
Typical cost
£100 – £250
Intermittent faults may require a longer visit. If data logging equipment is installed and a return visit is needed, expect costs at the higher end.
