What is this?
A buzzing or humming sound coming from your consumer unit (fuse box) is not normal and should be taken seriously. The consumer unit is the heart of your home's electrical system, distributing power to every circuit. Buzzing can indicate loose connections, a failing RCD or MCB, or overloaded circuits creating excessive current flow. Under BS 7671, all connections within a consumer unit must be tight and secure — any looseness creates resistance, heat, and potentially dangerous arcing.
Common causes
- Loose terminal connections inside the consumer unit
- Failing or worn-out MCB (miniature circuit breaker) that is not making clean contact
- RCD vibrating due to a small earth leakage current not quite large enough to trip it
- Overloaded circuits causing excessive current and magnetic hum in the busbars
- Corroded or damaged busbar connections
- Faulty main switch with degraded internal contacts
Is it dangerous?
Yes, this is potentially dangerous. A buzzing consumer unit often indicates loose connections, which cause arcing and heat buildup. Arcing inside a consumer unit is a fire risk, especially in older units with a plastic enclosure rather than a metal one. If the buzzing is accompanied by a burning smell, warmth on the unit casing, or scorch marks, turn off the main switch immediately and call an emergency electrician. Do not ignore this sound even if it seems minor — it typically gets worse over time.
Can I fix it myself?
No. You should never open or work inside a consumer unit unless you are a qualified electrician. Under BS 7671 (18th Edition), work within a consumer unit must be carried out by a competent person and is notifiable under Part P of the Building Regulations. What you can do is listen carefully to identify whether the sound is coming from a specific MCB or the whole unit, and check if the buzzing changes when you turn off individual circuits. This information is helpful for the electrician.
When to call an electrician
Call an electrician as soon as possible. If the buzzing is loud, constant, or accompanied by a burning smell or heat from the unit, treat it as an emergency. Even a faint hum that comes and goes warrants a professional inspection within a few days, as the underlying problem will likely worsen.
What will an electrician do?
Isolate the supply and remove the consumer unit cover to inspect internal connections
Check and torque-tighten all terminal connections to the manufacturer's specifications
Test each MCB and RCD for correct operation and replace any that are faulty
Inspect the busbar for signs of overheating, arcing, or corrosion
Perform a full load test to check for overloaded circuits
Recommend a consumer unit replacement if the unit is old, damaged, or non-compliant with current regulations
Typical cost
£100 – £300
Tightening connections and replacing a single MCB is at the lower end. If the consumer unit needs replacing, expect £350–£600 including labour and certification.
