Can I use extension cord for Tesla Mobile Connector?

[Dan Ji]

I have been charging my Model Y using mobile connector (120V). I have been using an extension chord because I charge the car outside of my garage most of the time. I just happened to read the mobile connector manual (see attached) and on page 5 it specifically stated not to use any sort of extension chord. Anybody know why? I have been using it for two months and I did notice the extension chord heated up a little bit (not to a point that is scary), and have not seem any problem. Shall I stop using the extension chord? Would like to hear some science behind why it is not recommended.

Thank you

 

[1965Falcon]

The problem with most extension cords is that they use 16awg or 14awg wire which is not sufficient for constant high amperage use and will have a pretty high voltage drop. This can damage things. At a minimum, use a quality 12awg extension cord and you should be ok as long as it's not to long.

 

[Earl]

Would like to hear some science behind why it is not recommended.

The Science is fairly easy. Smaller wire (which most extension cords are) have higher resistance (to the electrons flowing through the wire). Higher resistance causes more heating. The formula is P=(V^2)/R where P=Power (in the form of heat with a wire), V=Voltage, and R = Resistance (measured in Ohms). For any wire thickness and material, R is a function of the length of the wire (Ohms/meter).
If P is too large, so is the heat dissipated and it is a fire hazard.

 

[Dan Ji]

The Science is fairly easy. Smaller wire (which most extension cords are) have higher resistance (to the electrons flowing through the wire). Higher resistance causes more heating. The formula is P=(V^2)/R where P=Power (in the form of heat with a wire), V=Voltage, and R = Resistance (measured in Ohms). For any wire thickness and material, R is a function of the length of the wire (Ohms/meter).
If P is too large, so is the heat dissipated and it is a fire hazard.

So I need thicker chord to reduce the risk, what awg of the chord shall I get for NEMA 14-50 outlet?

 

[arnolddeleon]

The additional problem with an extension cord for mobile connectors is you defeat one of the safety features, the temperature sensor at the plug end. If your wall socket gets hot the UMC won't sense it because the plug is at the end of the socket end of the extension cord.

 

[Earl]

So I need thicker chord to reduce the risk, what awg of the chord shall I get for NEMA 14-50 outlet?

This was explained well by:

The problem with most extension cords is that they use 16awg or 14awg wire which is not sufficient for constant high amperage use and will have a pretty high voltage drop. This can damage things. At a minimum, use a quality 12awg extension cord and you should be ok as long as it's not to long.

The additional problem with an extension cord for mobile connectors is you defeat one of the safety features, the temperature sensor at the plug end. If your wall socket gets hot the UMC won't sense it because the plug is at the end of the socket end of the extension cord.

Also brings up a good point. I've melted an electrical outlet using the simple 120v charging cord for the Roadster. It didn't cause a fire or anything but it certainly scorched the outlet and the plug. Many household electrical outlets are cheap contractor-grade and can't handle sustained currents.
By using an extension cord, you are definitely taking the risks upon yourself. No professional will ever recommend using one.

 

[IvesSM]

I would go with a minimum of size 10 awg extension cord and only 25 or 50 ft at the most. For your constant draw you want a bit of safety on your side.

Also know where your closest fire extinguisher is. Keep it local to your power panel and any high voltage devices you have. It's cheap protection. Make sure it's rated for electrical fires too.

 

[karkrazy]

so not just the extension cord, but make sure you have a quality 14-50 outlet installed. Probably best to have a heat detector too.

 

[Earl]

so not just the extension cord, but make sure you have a quality 14-50 outlet installed. Probably best to have a heat detector too.

If you're going with 120v "level 1" charging, it will be a 5-15 or, better, a 5-20 outlet, not a 14-50 which is a 240v outlet.
Quality is key as well, forget the Leviton garbage that is normally available.

 

[John Whetsel]

I'm in the UK, i.e. 240V. How does that change the recommendations? Still go for a fat cable but what else?