Range Confidence: Charge Fast, Drive Far, with your Electric Car

By David Herron

Safely use Extension Cords when charging an electric car or electric motorcycle

Your electric vehicle was supposed to transport you around town and beyond. The problem is range and charging station availability. With enough public charging stations electric cars can drive any distance. Unfortunately between the 80-120 mile range of most electric cars and insufficient public charging, we face serious limitations. Does that mean we must be limited to traveling a short distance from home? No. The solution (for now) is knowing how to safely use existing power outlets with extension cords and portable charging stations.

Electricity is everywhere, and could theoretically power electric cars anywhere we wish to go.

If we only charge at home, we're limited to driving within a circle around our home. Public charging stations extends the area we can drive with, but that's still limited to areas with charging stations. Why should we allow either of these to limit where we can drive? Electricity is everywhere, why not access that electricity to drive anywhere?

Successfully electric car travel over long distances, at this time, means having the flexibility to use any power outlet you find, and the equipment to maximize the charging rate. You must understand some simple rules for safely use of (and maybe building) extension cords and adapter cables matching any power outlet.

The public charging network, and informal use of power outlets

Currently (2017) the public charging station network isn't enough to let us freely drive our electric vehicles anywhere we want. Most cities have public level 2 and even fast charging, but the inter-city charging network is weak. Even though electricity is everywhere, the electricity has to be adapted into a charging plug for recharging the car. The good news is we don't have to be limited to the public charging station network. There are plenty of high power electrical outlets available, and with the right equipment we can snag a 6 kiloWatt charging rate for a fairly reasonable charging time.

The car manufacturers provide a 120 volts 12 amps (1.2 kilowatts) line cord charger with each car. That unit is better than nothing, since you can always find a compatible power outlet.

The outlet shown to the right, a NEMA 14-50 outlet, is the primary objective for full-speed 6 kiloWatt electric vehicle charging away from both home and the public charging network. This, and other 240 volt 40 amp outlets, will let you charge at 6 kiloWatts continuous power. That's enough for 25 miles of range per hour of charging. (see Understanding charging rates and effective trip speed) Many RV parks have NEMA 14-50 outlets, making them potential informal charging locations.

The pieces of this puzzle are:-

  1. The power outlet
  2. Possibly an extension cord
  3. An "EVSE" (portable charging station) with J1772 charging cord
  4. Possibly a J1772 extension cord
  5. Charging port on the vehicle, and the on-board charger

Which end to extend? We can use an extension cord between the power outlet and the EVSE, or between the EVSE and the car. The safest is to use a J1772 extension cord between the EVSE and the car.

Safety Every step must be done safely. We bought our electric vehicles to, for example, help the climate. Getting on the evening news by causing an electrical fire negates the gain you might have achieved.

The charging protocol ensures safety between the car and the portable charging station. The risk comes from the power outlet you're using, and the quality of any extension cord you're using.

What's the charging rate? How many amps will be used by your car through a specific charging unit? Your car will support a maximum charging rate, often 6 kiloWatts. The owners manual will list the maximum charging rate, and some electric cars support changing the rate. The car and EVSE negotiate the charging rate depending on the capacity of the EVSE and car:

EVSE type Range per hour of charging Power required Circuit
Typical line charger 4 miles 120 volts 12 amps 120 volts 20 amps
3 kW EVSE 10-12 miles 240 volts 16 amps 240 volts 20 amps
4-5 kW EVSE 18 miles 240 volts 24 amps 240 volts 30 amps
6 kW EVSE 20-25 miles 240 volts 32 amps 240 volts 40 amps

What's the required power outlet and cord ratings? The electrical code's 80% rule says a "continuous load" must be limited to 80% of the rating of the circuit breaker and power outlets. The last column in this table tells you the required rating to support a given charging rate.

Ampacity is the measure of the maximum safe current (amps) we can use in a wire of a given thickness. Generally, the thicker the wire the more current it can carry. Wire thickness is measured in "gauge", and you may have seen this number used. A typical home extension cord is 14 gauge, for example. That wire gauge is completely insufficient and unsafe for the line-cord charger that comes with electric cars.

The 120 volt line-cord charger usually runs at 12 amps, and requires a 10 gauge extension cord. The 6 kiloWatt charging stations run at 32 amps continuous, and requires a 6 gauge extension cord.

More details see: Electric car charging within electrical code and power outlet limits

Wait, isn't it dangerous to use an extension cord to charge a vehicle?

Is it safe to use extension cords and adapters to charge an electric car? Yes, with care. Can you charge an electric car from a dryer outlet? Yes, with care. The short answer is to use a good quality extension cord with thick wires and beefy plugs. In the lists below we show several choices for 120 volt 10 gauge extension cords that are safe for use with a line cord charger, and several 240 volt 40 amp extension cords safe for use with higher power charging stations.

The best choice is a good quality J1772 extension cord. These cords are built for the purpose, and will safely handle a 6+ kiloWatt charge rate.

WARNING: Vehicle manufacturers universally warn against using an extension cord to extend the reach of the supplied line-cord charger. Please, exercise caution in reading what is written here.

The general principles are:

  • Check carefully the power socket rating
  • Check carefully the wiring to the power socket
  • Use heavy duty cables with high enough gauge to handle the current
  • Don't use cables that are frayed or broken
  • If you can, adjust the vehicle charger to not draw more current than you know is safe
  • Your power is limited by the weakest link in the chain - don't draw more through a circuit than its rating
  • Check whether cords or connections are getting hot while in use
  • Use the shortest length of cord possible

What is a substandard dangerous situation? A skinny cord, frayed wiring, bad power socket, acts like a "resistor" or "heating element". Sending too much current through a bad connection acts like a heater. Say your car is pulling 6 kilowatts, a 10% loss from a bad connection means 600 watts being dissipated as heat, or about the same as a typical hair dryer. That's a common cause of electrical fires.

Avoid violating Electrical codes Smart electricians and electrical engineers have spent decades cooperatively developing the electrical code. Their recommendations were won through hard work and the occasional electrical fire.

Your fate is in your hands - this is for educational purposes. I am offering this for education, and you are responsible for your actions. Applied incorrectly this can cause electrocution or fire. Take care, be smart and educated, and you'll be okay.

The need for safety: Done badly, it's possible to cause damage. The warning against extension cords isn't a whimsy, they're rightfully concerned about safety. Carefully done, you can safely ignore that warning, but you must know what you're doing. There have been multiple fires from electric cars being charged through substandard wiring. How? Bad wiring can easily cause enough heat to raise surrounding materials to the ignition point. This isn't a new issue since electrical fires have happened for as long as we've used electricity. Careful use of good quality extension cords and power outlets is the way to avoid an electrical fire.

JLong and De-ICEr - the best choice for an electric car extension cord

These are the most correct electric car extension cord because they're built to handle the load, with beefy wires and connectors. The two cords shown here support a 40 amp charge rate, and correctly connect the J1772 control wires all the way through. Cheaper J1772 extension cords do exist, but usually do not support the full charging rate.

A common problem at public charging stations is ICE'ing. This isn't a winter phenomena, but is an acronym: Internal Combustion Engine. What happens is gasoline car owners, whether unwittingly or on purpose, sometimes park in front of EV charging stations. Doing so blocks EV owners from charging. J1772 extension cords are a useful workaround until the people around us begin to grok charging station etiquette. See Charging station etiquette - effectively sharing limited resources

These extension cords can also be used at home. Say your charging station has a prescribed location, but your car has to park far away? The charging station might come with a 25 foot cord that doesn't reach the parking spot. What do you do? Use the J1772 extension cord.

The JLong 40 amp J1772 extension cable, from Quick Charge Power, and the De-ICEr 40 Amp 20 Ft J1772 Extension Cord for EV Charging Stations, from Electric Motor Werks, are both properly designed J1772 extension cords supporting a 40 amp continuous electrical load. Other J1772 extension cords max out at 32 amps, meaning the components aren't as high a quality. By supporting 40 amps, the wires are thicker, and the connectors more robust, making either a safer choice than the others.

I own a JLong, and am impressed with how solid and robust are the connectors. The cable is flexible enough to easily loop into a small bundle that's easy to carry in the trunk. Finally, there's a small but important detail - the charging handle can be locked using a simple padlock. This means your car won't be unplugged unexpectedly or at the very least the JLong won't be stolen.

J1772 extension cords are useful any time the charging cord isn't long enough to reach your car. Maybe you've been blocked from a charging station, but can park a couple stalls down. A J1772 extension cord like the JLong or De-ICEr gives extra reach.





Extension Cords

The following are some useful extension cords.

NOTE CAREFULLY: When in the store looking at extension cords, read the label carefully and look at the thickness of the wire.

Some of these have a molded plug on one end, and bare wire at the other. That makes them excellent starting points for building adapter cords. It's also possible to buy an extension cord, cut off the ends, and attach other plugs, to build a custom adapter.

NEMA 14-50 extension cords - 40 amps max charge rate

These will be primarily used with higher power 6+ kiloWatt charging stations. Every one of these extension cords have the beefy wires and connectors required to handle a 40 amps continuous charging rate. That's enough to handle any electric car charging situation you'll face.

Camco 55195 50 AMP 30' Extension Cord with PowerGrip Handle: This cord is rated for 50 amps, uses 6 gauge wiring, and has NEMA 14-50 connectors on each end. That is an excellent combination that will handle pretty much any current load you can throw at it.

General Electric WX9X35 4-wire Range Cord, 4-foot: 40 Amp, 4 wire, Range power cord This 4 foot cord is rated 40 amps, 125/250 volts, with two 8 gauge wires and two 10 gauge wires. This cord is a useful starting point for building 14-50 adapter cables

PETRA 90-2028 10-Foot 4-Wire Dryer Cord: 40 Amp, 4 wire, Range power cord This 4 foot cord is rated 40 amps, 125/250 volts, with two 8 gauge wires and two 10 gauge wires. This cord is a useful starting point for building 14-50 adapter cables

Coleman Cable 09014 6/2 and 8/1-Gauge SRDT 50-Amp Range Power Supply Cord, 4-Feet, 3-Wire, 125/250V: Coleman Cable 09014 6/2 and 8/1-Gauge SRDT 50-Amp Range Power Supply Cord, 4-Feet, 3-Wire, 125/250V. Right-angle plug allows installation closer to the wall. Has a 3 prong plug. 50-Amp. 4-feet long wire with strain relief bracket to ensure safe installation.

NU-CORD 25 ft. 6/3 8/1 NEMA 14-50 RV Extension Cord: Using 6-gauge wiring and molded plugs, this extension cord has the heft required for the task at hand. The plug/connector ends have built-in handles for easier handling. Home Depot also carries a

Utilitech 6-ft 50-Amp 6-Gauge Black Indoor Extension Cord: This cord is rated for 50 amps, uses 6 gauge wiring, and has a NEMA 14-50 connector on one end. The other end has bare wires apparently meant to wire into some equipment, but of course you can attach another plug on that end. That is an excellent combination that will handle pretty much any current load you can throw at it.

NEMA 6-50 extension cords - 40 amps max charge rate

These are the same as the NEMA 14-50 cords, but with 6-50 connectors instead. They also support a 40 amp charge rate, and will handle any charging situation you'll face.

Milspec Direct 25-Foot 8-Gauge STW Pro Grip 40A Welding Extension Cord for Portable Welders, Black: Professional quality patented Pro Grip lighted welding extension cords bring power to where you need it. Todays portable welders have power supply cords that are much too short. Rated at 50A-250V (NEMA 6-50), each extension cord features two clear neon lighted ends that allow you to make sure power is flowing through your cord. In addition, the bright neon lit ends illuminate in the dark and visually makes the connects and disconnects easier to do. The specially crafted, high visibility jacket on Pro Grip cords are designed to be Flame Retardant (FT2), Water Resistant (WR), and Cold Weather Resistant (-40F). Patented Pro Grip nylon handles make pulling apart plugs and connectors from each other easier with less effort and stress. Pro Grip handles easily fold away when not in use.

Coleman Cable 1917 8/3 STW 6-50 Welder Extension Cord, Blue, 25-Foot: Coleman Cable 1917 8/3 STW 6-50 Welder Extension Cord, Blue, 25-Foot. 8-Gauge plug. Stw jacket for heavy-duty performance. Lighted receptacle end indicates when power is on. Molded ends offer safety and convenience on the jobsite. Bring portability to welding machines and create convenience. Provide a convenient, safe method to extend the range of welding equipment. Intended for new commercial construction, mro industrial and general welding.

NEMA L14-30 extension cords - 24 amp maximum charging rate

The outlets rated for 30 amps are useful with the 16 amp or 24 amp charging stations. Using these outlets may require buying or building an adapter cord to match the EVSE's plug to the power outlet.

Iron Box # IBX-5805-50M - 30 Amp L14-30 Generator Extension Power Cord - 4-Wire, 30A, 125/250V, UL LISTED: Heavy duty UL listed L14-30 generator extension cord rated for outdoor use. 50 foot length, uses a heavy duty flexible SJOOW jacket. For use with generators that feature an L14-30R receptacle. Cable generally extends another L14-30 power cord plug, or connects to a transfer switch or inlet box with a male L14-30P inlet.

Conntek 20602 50-Foot 10/4 30 Amp 125/250 Volt 4 Prong L14-30 Transfer Switch Cord/Generator Extension Cord: Generator Extension Cord, 3 Pole, 4 Wire Grounding, NEMA L14-30P to NEMA L14-30R Max Power: 7500W, Stays flexible in cold weather, Heat Resistant up to 221F Application:Transfer Switches, Generator,...etc. Approval: Plug, Connector, : UL, C-UL Cable: 50FT STW 10/4 rating:30A 125/250V

Coleman Cable 01912 25-Feet 10/3 Generator Power Cord with L5-30P Plug and 3-Outlets: The Coleman Cable 01912 25-foot 30 Amp 10-gauge Tri-Source (locking male) generator cord plugs into 30 Amp locking outlets on a generator. The Tri-Source female end provides three extra 15 Amp standard outlets, while the vinyl jacket protects against moisture, abrasions, and exposure to sunlight. The cord features one male 5-20P plug with three 5-15 female outlets, is rated for rugged outdoor use, and is engineers specially to work with portable generators.

NEMA L6-30 extension cords - 24 amp maximum charging rate

Ditto.

NEMA L6-30 Extension Power Cord - 20 Foot, 30A/250V, 10/3 SJOOW - Iron Box Part # IBX-5803-20: NEMA L6-30 extension power cord allows you to extend an L6-30P power cable up to 20 feet. Rated for 30 Amps, 250 Volts. L6-30P plug to L6-30R connector.

L6-30 Extension Power Cord, 15 Foot - 30A, 250V, 10/3 Wire: A 15 foot L6-30P to L6-30R locking extension power cable, rated for 30 amps and 250 volts. Used typically in rackmount PDU's, servers, UPS, and generators.

NEMA 6-20 extension cords - 16 amp maximum charging rate

Ditto, and the 20 amp outlets are limited to use with 16 amp charging stations.

NEMA 6-20 Extension Power Cord - 25 Foot, 20A/250V, 12/3 SJT - Iron Box # IBX-6153-25M: This is a simple 25 foot extension cord with molded plugs for NEMA 6-20. It would be a great companion to the AeroVironment TurboCord shown above.

Stanley 31626 Grounded 250-volt Heavy Duty Appliance Pro Extension Cord, 6-Feet, Gray: This Stanley Appliance Pro heavy duty 6-Foot extension cord will handle most of your appliance needs where the distance to the outlet occurs. It is a 250 volt cord and has a gauge of AWG 12/3 SPT. The Right angle plug will sit flat against the wall. It has a heavy duty vinyl insulation.

NEMA 5-20 extension cords - 16 amp maximum charging rate

The 120 volt power outlets are limited to use with the line cord EVSE sold with the car. When looking at 120 volt extension cords you must be very careful with the wire gauge. The typical skinny 14 or 16 gauge extension cord simply won't cut it for EV charging. You must use a heavy-duty cord with 10 gauge wires and good quality connectors.

Yellow Jacket 2806 10/3 Heavy-Duty 15-Amp SJTW Contractor Extension Cord with Lighted End, 100-Feet: Yellow Jacket 2806 10/3 Heavy-Duty 15-Amp SJTW Contractor Extension Cord with Lighted End, 100-Feet. Super flexibility in cold and hot weather. Power Lite power indicator lamp glows through the extra heavy, clear molded plug when the cord has power. Three times as abrasion resistant as standard vinyl, making these cords the toughest on the jobsite. Extra heavy, clear molded plugs are rugged, durable and oversized. Meets OSHA specifications, UL Listed. 10 Gauge.

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100 ft. 10/3 SJTW Extension Cord with Lighted Plug: Meant for heavy-duty applications, this 10 gauge cord is also light-weight and easy to roll into a compact unit.

Utilitech 50-ft 20-Amp 110-Volt 10-Gauge Yellow Outdoor Extension Cord: This cord is rated for 20 amps, uses 10 gauge wiring, and has a NEMA 5-20 connectors on each ends. The connectors light up when powered, and the bright yellow color should mitigate tripping hazards. That is an excellent combination that will handle your line cord charger with ease.

Commercially built adapters

You won't always find the nirvana of matching the charging station to the power outlet. An adapter, whether commercially made or home-made, is often necessary. Be careful with adapters to avoid the position of drawing 32 amps from an outlet rated for 16 amps. If you're lucky the circuit breaker will prevent a serious problem.

NEMA 6-50 to L14-30, 240 volt 30 amp

NEMA 6-50 to 14-50, 240 volt 50 amp

NEMA L14-30P to NEMA 14-50R, 240 volt 30 amp

NEMA 14-30P to NEMA L14-30R

NEMA L14-30P to 6-15/20R

NEMA-L5-20R to NEMA-5-20P, 120 volt 20 amp

NEMA 14-50 to TT-30

The TT-30 outlet is 120 volts up to 30 amps (24 amps continuous).

Camco 55185 PowerGrip 30M/50F AMP 18 inch Dogbone Electrical Adapter with Handles 3750W/125V: This adapter converts between NEMA 14-50 and NEMA TT-30P (30 amp).

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Camco 55175 18 inch PowerGrip Dogbone Electrical Adapter with Handle: This adapter converts between NEMA TT-30P and NEMA 14-50 (30 amp).

Ground Fault protection

Charging an electric vehicle is almost certainly going to happen outside. It might be raining. Water and electricity is of course a bad idea. GFCI plugs are designed to make it safe.

Voltec 04-00102 12/3 STW 20 Amp GFCI Power Block Adapter with Lighted End, 3-Foot, Blue with Yellow Stripe: 20 amp in-line GFCI adapter with lighted power block, length: 2ft, gauge: 12/3, wire type: STW, 3 outlets, plug type: 5-15P, receptacle type: 5-15R, 20 amps, rating watts: 1875. In other words, this is a short extension cord with GFCI. It is only suitable for a level 1 charger, but will be good insurance.

Tower Manufacturing 30396500-08 20 amp Line And Load Side User Attachable In-Line GFCI With Manual Reset: This unit fits over a cord, giving you strong protection from the elements, while providing GFCI protection.

Leviton WT899-W 20-Amp 125-Volt SmartLock Pro Slim Weather-Resistant and Tamper-Resistant GFCI Receptacle, White: A regular power outlet with GFCI protection. For use in the field, you can install this in a junction box and run wiring into it. However, it is little better than the extension cords, and of course this is limited to level 1 charging.

Tower Manufacturing 30339005 15 amp 3-Wire GFCI Outlet Adapter: 15 amp 3-wire ground fault circuit interrupter (GFCI) outlet adapter for converting standard indoor electrical outlet into GFCI outlet to protect from shock, electrical fire or electrocution. This is an in-line plug/socket making it a little simpler to use than an extension cord. However, it is only rated for 15 amps limiting its usefulness somewhat.

Farm Innovators CC-2 Cord Connect Water-Tight Cord Lock - Green: This is not a GFCI protector at all, instead it fits over cable connections, giving strong protection against the elements.

Sockets and Plugs

These products are useful for building custom adapter cords.

NEMA 14-50 - 240 volt 50 amp

NEMA 6-50 - 240 volt 50 amp

NEMA L14-30

NEMA L6-30 - 240 volt 30 amp

NEMA L6-20

NEMA 6-50, 6-30, 240 volt, 50 amp, 30 amp

Cooper Wiring Devices S42-SP-L Commercial Grade Angle Vinyl Power Plug with 30/50-Amp, 250-Volt, 6-30/6-50-NEMA Rating, Black: The commercial grade angle power plug has feature dual current model furnished with blades. Terminals have pressure plates to protect wires. This device is constructed of abuse-resistant thermoplastic. 30/50-amp, 250-volt, 6-30/6-50-NEMA rating and 3-pole, 3-wire grounding configuration. Available in black color. Measures 2-7/8-Inch length by 1-3/8-width by 3-3/8-Inch height.

Leviton 931 30/50 Amp, 250 Volt, Plug, Angle, Grounding, Black: * 2 pole, 3 wire grounding dual power angle plugs with interchangeable blades * Dual power vinyl angle plug - interchangeable blades * 250 Volt * 60 Hz AC Grounding * Molded of tough, black vinyl * Heavily plated steel cable clamp concealed in plug-protected from wear prevents catching on equipment or clothing * Meets all range, dryer and other heavy duty cord requirements * Color-coded terminal screws accept up to No. 6 stranded conductor * Terminal screws are backed out and staked * 3.484"L x 2.562"W x 1.427"D * 30/50 Amp * Maximum cord diameter -.630 - 1.050" * Interchangeable blades * NEMA (6-30P) (6-50P) * Black height.

NEMA 6-20

Leviton 620PV 20 Amp, 250 Volt, Plug, Grounding, Yellow: 20 Amp, 250 Volt, NEMA 6-20P, 2P, 3W, Plug, Straight Blade, Commercial Grade, Grounding - Yellow

NEMA TT-30P

Heavy duty wire/cable

Wire Cord, 50 Ft, Rubber Coated, 10 Gauge, 4 Conductor (10/4) 600v SOOW: 50 foot long Rubber SOOW cord is designed for indoor or outdoor applications. 4 conductors can be stripped and installed in many types of power connectors including L14-30, 5-30, 6-30, 7-30, 24-30, 10-30, 11-30, 15-30 or 18-30. Suitable for use with RVs, Generators and Theater lighting.

Coleman Cable 09607 10/4 Bulk Wire, 25-Amp 10-Gauge 25-Feet: Coleman Cable 09607 25-Feet Bulk Wire 10-Gauge 4-Cond SJEOOW Seoprene Rated 105-Degree Celsius, 10/4 Flexible and tough jacket. Offers -50-Degree Celsius to 105-Degree Celsius temperature extremes. Seoprene offers excellent abrasion, ozone, sunlight, chemical and oil resistance as well as water and mold resistant non-wicking lightweight polypropylene fillers. Water resistant with high dielectric insulation. Lightweight, long lasting, easy to carry and easy to handle. All components are recyclable and non-hazardous for environmental landfill disposal. Color coded conductors for easy identification. This type of wire has many applications, they include Special uses requiring flexibility and mechanical toughness, high environmental resistance and flame retardance. Push button remote controls. Motor control, stage equipment and lighting. Industrial control and robotic systems. Outdoor applications. Suitable and approved for submersion in water.

Safely use Extension Cords when charging an electric car or electric motorcycle

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