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What is the best extension cord for EVs? The Easy Way

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Mike Becker

As a response to an article about Tesla public charging stations, I have received many inquiries asking what kinds of extension cords should be used with electric vehicles (EV), especially Tesla.

Therefore, this article will focus on answering the following questions: What kind of extension cord is safe for use? How do I use it safely? Earlier in the article from Mike Becker, it was noted that the EV charger extension cords differ according to the type of socket. So for Tesla, some extensions will fit, and for Nissan others.

How to choose the right extension cord

An extension cord is a temporary substitution for a permanent power supply. It should be able to handle the expected load and selected device without overheating or overloading, and it must have sufficient length to reach from the wall socket to the closest outlet where an EV will park. For certain duty cycles (high wattage appliances drawing on electricity), the extension cord should be able to handle the additional current and voltage drop.

For most EV charging needs, one can buy a 25 ft. extension cord from Home Depot or Lowes for about $100. However, it might not be certified by Underwriter Laboratories (UL). The NEC requires that all cords have the stamp of approval from a Nationally Recognized Testing Laboratory (NRTL) or Intertek, which means it has been tested for electrical properties and safety. 

NEMA 15-50 extensions

NEMA 15-50 is a group of electrical extension cords used for temporary power needs. The abbreviation "NEMA" stands for the National Electrical Manufacturers Association, an association of manufacturers who make industrial and commercial electric products; their standards are published in documents called NEMAs. 15-50 stand for the standard that says these cords have a rated voltage of 15 amps and 50 feet in length. Extension cords such as this one come with outlets on both ends so they can be plugged into another outlet or power strip, to lengthen their reach.

J1772 extensions

The J1772 is a type of electrical plug that can be used for electric vehicles, including cars, motorcycles, and boats. The standard was created by the Society of Automotive Engineers (SAE) in 2008. A part of this standard requires the cord to be rated at 125V or 250V and 16A maximum.

By 2018, vehicles are expected to come with a different plug known as SAE International's "Combo 2" which has four pins instead of five.

This new version may require an adapter similar to ones found on small electronics like cell phones and laptops.

A key advantage to using the J1772 plug is it can include various safety features such as Over-temperature protection so the extension cord stops working if the internal temperature gets too hot, and over-current protection which stops the cord from working if it is overloaded.

Selecting extension cords for your home can be hard.

Extension cords provide convenient, temporary power to electrical devices from a source other than the main electrical system. You can use an EV extension cord with household appliances and tools, or you can connect it to an outlet in one room of your house and run it through walls or windows to an appliance in another room. The National Fire Protection Association's (NFPA) standards help ensure the safe and proper use of electric car extension cords. NFPA offers these recommendations for using electric vehicle extension cords:

  • Avoid Using More Than 3 Extension Cords On One Electrical Circuit
  • Number And Use Labeled Extension Cord Plugs Sequentially On A Single Circuit
  • Use An Extension Cord With A Grounded Outlet To Prevent Electrocution

When selecting an EV extension cord, select one that is heavy enough to carry your device's power needs and has no visible damage or wear. Don't use damaged cords; have them replaced by an electrician if necessary. Avoid using older 3-wire extension cords for new, grounded, 3-pronged plugs as these older cords may not be able to accept the current demands of more powerful electronic devices and could overheat when used in this fashion. To confirm that old 3-wire extension cords are safe, check the plastic plug at the end of the cord to see if it has a third, round, prong (the ground wire). If your extension cord lacks this safety feature, get an adapter or replace the cord. It is safest to use J1772 as an extension.

All in all, select NEMA for Tesla. And for non-Tesla cars, choose a J1772 extension cord. The NEMA 15-50 is a commonly used power cord in residential and commercial outlets. It's considered safe for use in all weather conditions, and it comes with its own grounded plug so users don't have to purchase that separately. The 50 feet of length covers most outdoor needs where an outlet isn't available.

 

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