Extension cords should not be more than 100 feet long. Moreover, for the NEMA 14-50, you will often only find 50-foot lengths on the market. J1772 cables are usually even shorter, at 40 feet. The maximum length of an extension cord may be exceeded by adding one extension cord to another, but this is dangerous and often leads to overheating. If the work is more than 100 feet long, a temporary power distribution box is necessary for NEMA.