Can you jump a car battery with an extension cord (or ordinary electrical wire)?

It is advisable to use a factory-made of good quality jumper cables instead of an extension cord or ordinary electrical wire because it is built to handle the high currents drawn by the car’s starter reducing the risk of fire and injury to yourself from the burns.

In addition, the factory-made jumper cables are:

  • adequately sized (usually wire gauges 1, 2, 4) to safely carry the high starting currents of the car
  • Long enough to conveniently connect to another car’s battery parked 10ft or 16 ft away for purposes of jumpstarting
  • Lower risk of damage to the car from accidentally interchanging the cables

Lastly, they have strong alligator clamps that make firm battery connections, keeping voltage drops to a minimum so your car starts right away.

Summary: Why you should NOT use ordinary electrical wire or an extension cord to jumpstart your car battery

No.Extension cordQuality set of jumper cables
1Risk of fire – the AWG gauge wire typically handles 10-15Amps safelyLow risk of fire – suitably sized AWG gauge to handle several hundred amps
2Difficult to attach to battery terminals – no clamps to attach wires to battery terminalsReduced voltage drops – alligator clamps make firm connections
3Higher risk of damage to car starter from wrong polarity connections (wires usually not colour coded)Colour-coded cables minimize the risk of making accidental cable connections that may damage the starter

Extension cord wires are thinner, generally difficult to make firm and safe connections with and there is a high risk of connecting cables the wrong way that can damage the car starter.

How to select jumper cables

There are many types of jumper cables on the market with different features, current handling capacity and length. In this section, I will point out the ones that can help you make a better choice of jumper cable.

Length of cables. Aim for longer jumper cables whenever possible. You can use them to jumpstart a car easily even when the car with a good battery is parked over 15 feet away. Jumper cables may come in various lengths such as 10, 16, 20, 25 or 30ft. 16 feet is good enough for small cars, 20 feet pickups and 30ft for light trucks

Copper vs. aluminium jumper cable. Ideally, you want the jumper cables made of copper because of its low electrical resistance however, more and more cables are made from copper-clad aluminium. It is cheaper and has good performance reviews.

Additional feature set. Does your set of jumper cables have extra features such as reverse polarity indication to alert the user should the jumper cables be connected the wrong way? Does your set of jumpers have a battery tester? Whenever possible get jumpers with these features!

How to connect jumper cables the right way

You can follow the 3 step process below to connect your jumper cables the right way.

# 1. Start the car with a good battery and keep its engine running

# 2. Connect the red cable clamp of the jumper cable on the positive terminal of the good battery and the other end to the positive of the weak or dead battery.

# 3. Next, connect the clamp of the black wire to the body of the car with the good battery and the other end of the black clamp to the body of the car with the weak or dead battery.

# 4. Double-check the connections to make sure that the black cable connection is made on the body or negative terminals of the battery and the red cable connections to the positive terminal.

After completing the above connection, attempt to start the car with the weak or dead battery.

Are your jumper cables are working?

Sometimes after making the proper connections, your car may fail to start and you need an easy way to confirm the jumper cables are working. Here are 3 signs you can look out for to tell that your jumper cables are working.

If the car with the good battery has its engine is running, you can expect:

  • to see a small spark as you make the last jumper connection to the positive terminal (always connect the negative terminal first)
  • the engine rpms of the car with the good battery to reduce – a sign that the car with the good battery’s alternator is now charging the weak or dead battery
  • The dashboard lights in the car with the weak or dead battery light up. If you see any of the above signs and your car still fails to start, you need to investigate other possible causes of your car’s failure to start.

Related questions

# 1. Should you plug a battery charger into an extension cord?

While you may be able to plug a low amp battery charger into an extension cable to extend the power supply to the charger, this is generally not recommended.

Instead, you should aim to plug the battery charger plug directly into the wall outlet and electrical circuit with sufficient power for the battery charger.

This is because the current draw of battery chargers >13A to overload, destroy and increase the risk of fire as household extension reels are typically rated 13-15A maximum.

If you must use an extension cord, make sure:

The AWG wire size of the extension code can handle the amperage of the charger. Check out our guide on sizing wires for AC applications.

the extension cord plug pins size and number should match that of the battery charger. In particular, make sure that the extension cord is providing a good ground connection to reduce the risk of electrical shocks.

Make sure the AWG wire size used in the extension cord is long enough to minimize voltage drops that can affect the performance of the battery charger.

Here is an indicative guide of the AWG size of electrical cord wire to use for different lengths of the wire (Consult your battery charger manufacturer for guidance)

No.Length of extension cord (feet)AWG wire size
12516
25012
310010
41508

In general, avoid using an extension cord or ordinary wire as jumper wire to avoid the risk of fire and injury when the car starter draws a high starting current.

Using jumper wires instead, the AWG wire size is suitably sized to handle the high starting currents. Furthermore, it is color-coded (may also have reverse polarity indication) to alert you in case you accidentally swap the cables.

Related Topics

What amperage should you set when charging your AGM battery
Why your car battery may be dying quickly
Why overcharging of car batteries is bad

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