Incompatible Receptacle Leads to Potential Fire Hazard

Recently, the Mission Fire Department responded to a call from tenants in a single family home who smelled a burning odor coming from the living room. The fire fighters investigated the scene using a thermal imaging device to find a hot spot around an electrical outlet box. After turning off the circuit breaker in the electrical panel, one of the responding fire fighters, who was also an electrician, removed a receptacle from the outlet box to reveal that the receptacle was not compatible with aluminum wiring.  Technical Safety BC later found similar instances of the aluminum wiring that terminated onto devices only intended to have copper conductor terminations throughout the 40 year-old house.

The original home was believed to have come with #12 awg aluminum branch circuit wiring and a 100 Amp , 120/240 Volt rated, overhead electrical service that appeared to be original equipment. The outlet box discovered looked to be a retrofitted box with wiring and receptacle that were likely altered by an unqualified person. The receptacle involved in the incident was a 15 Amp, 120 Volt rated, ground fault circuit interrupter (GFCI) duplex receptacle.  This receptacle, like many others found around the house,  was not compatible with the  aluminum wiring. Through regular use, the electrical connection between the aluminum wiring and the receptacle loosened, contributing to localized heating for the receptacle involved in the incident. Heating at the connection progressed with continued use until it was detected by the tenant by popping sounds and the smell of smoke.

There was no evidence of damage on the front of the receptacle, which made it more dangerous for the tenants inhabiting the house, as they unknowingly continued use of the improperly installed receptacle. Inside the wall, the back of the receptacle’s plastic body had begun to melt, deform and discolour. The insulation of the conductor also melted and internal electronic components were damaged. A closer look by Technical Safety BC's safety officer determined that the receptacle was CSA approved and the receptacle’s manufacturer had labelled the receptacle for copper wire use only for all connections.  The tenants had indicated that they only plugged a small string of lights into the receptacle at the time of the incident, which bore the approved certification mark for electric products.  With variable causes ruled out, it was determined that the incident was a result of an incompatible receptacle installed on aluminum wiring.

The cause of this incident reminds us of the BC Electrical Code rule 2-024, which requires electrical equipment to be approved for the specific purpose for which it is to be employed.  

Fire hazard: The back of the damaged receptacle cut from #12 awg aluminum house wiring. Clearly marked on the receptacle: “USE COPPER WIRE ONLY FOR ALL CONNECTIONS” along with Cu (copper) symbol and the ‘no AL (Aluminum)’ symbol.

Bedroom receptacle also had aluminum conductors terminated directly to the receptacle. The bonding conductor of the branch circuit wiring was not connected to the outlet box or the receptacle as required by code.

For more on this topic, see: Does your home have aluminum wiring? What you need to know.