The National Highway Traffic Safety Administration is investigating 50 Bosch Power Xpress 240-volt charging units after receiving a consumer complaint last summer.

The complaint stated that a 2013 Nissan Leaf began to emit smoke while the vehicle was being charged.

Smoke was seen "around the vicinity of the vehicle/charger interface" when the vehicle was charging at a private residence. The owner of the vehicle was using a Bosch Power Xpress 240V charging unit to charge the Leaf model.

"According to the owner, the vehicle had been charging for approximately one hour at 30 amps when signs of overheating were first noticed. The overheating condition can cause damage to the vehicle and charger, rendering both inoperable," the NHTSA said in a statement.

Steve Yaeger, a Nissan North America spokesman, said earlier this week that Nissan will "assist regulators and Bosch with this investigation as needed," according to Edmunds.

"This inquiry is focused on the electric vehicle charger and is directed at the charger supplier, Bosch," Yaeger added.

The NHTSA has not identified the Nissan Leaf owner yet. The complaint was filed in late August 2013, according to the safety administration.

The car was less than five months old, and had well under 10,000 miles on its odometer.

"The connection had gotten hot enough to melt the plastic and create smoke, indicating a fire," the complaint reads. "Nissan has determined by pictures that the car was not to blame for the incident. They are blaming the charging station for the failure. They have denied any warranty coverage."

A preliminary evaluation into the issue has been opened by safety regulators, which often leads to a recall.

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