A burning smell from an electrical fitting, socket, switch, appliance, or consumer unit is a warning sign that should not be ignored. Electrical arcing, overheating connections, and insulation breakdown can all produce a smell ranging from a faint warm plastic odour to a sharp acrid smell.
Identifying the source and stopping further use of the affected circuit or appliance is the correct immediate response. The smell may originate from a single appliance that has developed an internal fault, from a loose connection in a socket or switch causing arcing under load, from wiring carrying more current than it was designed for, or from a deteriorating connection in the consumer unit.
In properties where wiring has not been assessed for many years, insulation can become brittle and begin to break down, generating heat and odour before any visible damage appears. If you detect a burning electrical smell, stop using the affected equipment.
Disconnect an appliance only if safe: do not touch a hot, sparking, damaged or smoking plug or fitting. If there is fire or smoke suggesting a fire, get out, stay out and call 999; do not delay evacuation to investigate or isolate electricity.
If the smell appears to come from a socket, switch, light fitting, or the consumer unit, switch off the relevant circuit at the consumer unit if you can do so safely, and avoid using that circuit until an electrician has assessed it. Do not assume a burning smell will resolve itself.
Overheating connections and deteriorating insulation tend to worsen over time and represent a fire risk. A qualified electrician can assess the installation and select appropriate visual checks and electrical tests before an agreed repair.
Customers should not energise a suspect circuit to reproduce an overheating fault.