This is related to several safety and performance considerations:

1. Safety: An extension cord can increase the risk of overheating, fire hazard, and electric shock. Since charging an electric car requires high power, the electrical current must be transferred efficiently. An extension cord can lead to voltage drop, heat buildup, and overload, especially if it is of insufficient quality or not suitable for the expected power.
   
   

2. Cable thickness: When charging an electric car, it is important to have the correct cable thickness to allow sufficient power transfer without overheating. Extension cords are usually designed for lighter appliances and often have a smaller cable diameter, which can lead to increased resistance and heat development when charging a car.
   
   

3. Certification and standards: Charging cables specifically designed for electric vehicles meet strict safety standards and certifications to ensure a safe and reliable charge. Extension cords may not be suitable for charging electric cars and may not meet the required standards.
   
   

4. Reduced performance: Using an extension cord can decrease charging efficiency and slow down the charging speed. The extra length and resistance of the cord can lead to energy loss and longer charging times.

To ensure safety and achieve optimal performance, it is advisable to use a charging cable of adequate length that is suitable for the expected power of your electric car. If you do not have a suitable outlet nearby, you might consider installing an additional charging point at a convenient location.

It is always advisable to consult the instructions and guidelines of your electric vehicle's manufacturer and the charging equipment, and seek advice from a certified electrician or supplier if you are unsure about the correct way to charge your car.