Safely use Extension Cords when charging an electric car or electric motorcycle
Your electric vehicle is meant 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 limit where we can drive? Electricity is everywhere, why not access that electricity to drive anywhere? At this time that means developing knowledge of some simple rules for safely using extension cords and adapter cables matching any power outlet, and carrying with you a high power charging station.
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. Electricity is everywhere, but has to be adapted into a charging plug for use with the car. Accessing a high power electric outlet with a portable high power charging station means we don't have to be limited to the public charging station network, and can charge at a reasonable rate nearly anywhere.
The car manufacturers provide a 120 volts 12 amps (1.2 kilowatts) line cord charger with each car. In a pinch that station can be used anywhere to get some electricity into the car, but at 4-5 miles range per hour of charging you'll be parked for a long time. They're great at home or anywhere else where a long recharge time is acceptable.
The outlet shown to the right, a NEMA 14-50 outlet, or other 240 volt 50 amp outlets, are 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 40-50 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:-
The power outlet
Possibly an extension cord
An "EVSE" (portable charging station) with J1772 charging cord
Possibly a J1772 extension cord
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.
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:
Range per hour of charging
Typical line charger
120 volts 12 amps
120 volts 20 amps
3 kW EVSE
240 volts 16 amps
240 volts 20 amps
4-5 kW EVSE
240 volts 24 amps
240 volts 30 amps
6 kW EVSE
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.
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.
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.
J1772 electric car extension cords are the best choice, if built right
The most correct electric car extension cord fits between the J1772 plug from the charging station to the J1772 socket on your car.
Think about the concerns just raised: skinny frayed extension cords plugging into dodgy power outlets that might cause an electrical fire. We can avoid that with an extension cord that you know is built for the purpose, from components rated to the load that will be carried, is the safest choice. Some considerations that will separate the good quality J1772 cords from the bad:
Ratings: As with every other component in the charging system, the J1772 extension cord must be rated to handle the current shown in the chart above. For a 6+ kiloWatt charging session, the cord needs to be rated for at least 40 amps, for example.
Wire size: To be useful, a J1772 extension cord has to be 25 feet or longer, which can mean a significant voltage drop with thin wires. For a 6+ kiloWatt charging session, the wires should be 8 gauge or thicker, going by the ampacity charts referenced earlier.
Flexibility: Your J1772 extension cord will be used in a variety of settings, so a flexible cord is a must.
The JLong is perhaps the best J1772 extension cable available. The 40 foot length means it can get you out of more sticky situations than other shorter cords. That it is rated for 40 amps peak it can handle a full 32 amps continuous. The components are all solid and well-built. The J1772 handle includes a little hole allowing you to add a lock (that is included) for a touch of safety.
The EV Everything J1772 extension cable has a 20 foot length that will be useful in some cases, but other makers supply longer cords making them more useful. The product description says it supports 32 amps, but does not make clear whether this means 32 amps continuous. It may mean it supports 32 amps peak, in which case it would be limited to 24 amps continuous. It is unclear why this would come with a charging cord holster since the purpose is to bring it with you.
The following are some useful extension cords for use with an electric car charging station. Since they're designed for regular power outlets, they fit between the charging station and a power outlet.
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. Simply attach the desired plug or socket to the end with bare wires.
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.
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.
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.
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. 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.
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.
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
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. 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.
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.
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.
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.
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.
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.
* 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.
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 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.