Tesla does not recommend the use of extension cords at all with the Model S. If you elect to get an extension cord, make sure it is properly rated for the current you plan to use and has the connections that match your adapters. Charge times may be reduced slightly due to the resistance of the extension cord.
There are 240 VAC extension cords available, but be prepared for a heavy extension cord and a high price! For 120V, it should be 10-12 gauge, similar to the one below. These are recommended from other Model S users who have had good success with these cords:
- Camco 240V, 50 amp, 30′ Extension Cord
- Coleman 120V, 15 amp, 25′ 10/3 Vinyl Outdoor Extension Cord with Lighted End, 25-Feet
You can also make your own, if so inclined. Here’s a great writeup on making your own adapters and extensions cords for the Tesla.