The carmaker said that ‘a variety of factors such as corrosion, physical damage to receptacles, or inappropriate wiring or installation of electrical outlets can cause higher than normal electrical resistance when using the Universal Mobile Connector (“UMC”) NEMA 14-50 adapters to charge Tesla Model S vehicles. When charging, higher than normal electrical resistance connections to external energy sources may cause excessive heating of the adapter.’

The latest move follows the December release of an over-the-air software update to address this issue, enabling the Model S onboard charging system to automatically reduce the charging current by 25% if it detects unexpected fluctuations in the input power to the vehicle.

The carmaker said that it believes that this software update fully addresses any potential risks. However, to provide another layer of assurance to Model S customers using the 14-50 socket, it designed an improved wall adapter with a thermal fuse. Even if the circuit breakers on the house side and car side don't trip, the thermal fuse will prevent current from flowing if the wall socket region heats up for any reason.

The upgraded adapter is being provided to existing and new customers free of charge starting in a few weeks.

The announcement follows the news of a small number of fires that occurred in cars following crashes. Tesla said its review to date points to the building receptacle or wiring as the primary cause of the failed adaptors but said that it had decided a voluntary recall was appropriate as a precautionary measure.

In addition, Tesla has informed the National Highway Traffic Safety Administration of its proactive measures.

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