Jumping a car with a dead battery is a common occurrence for many drivers. It involves using jumper cables to connect the battery of one vehicle to another to transfer electricity and start the car with the dead battery. When hooking up jumper cables, it’s crucial to take proper safety precautions – and one of those is to always connect the negative cable last when jumping a car. Here’s a closer look at why you don’t want to connect the negative cable first.
The Risks of Connecting the Negative First
If you were to connect the negative jumper cable to the dead battery first, you could cause a serious spark when you go to attach the other end to the good battery. This is because you are introducing the negative lead to the dead battery before the positive lead. The dead battery can have a build up of hydrogen gas from sulfation, which is highly flammable. If you create a spark near that gas by connecting the negative first, it could ignite and cause an explosion.
Always connecting positive first avoids this dangerous scenario. The positive lead will allow you to complete the circuit safely without any sparking near the dead battery.
Here’s a quick overview of the risks associated with connecting the negative first:
- Can create a spark near hydrogen gas buildup in dead battery, risking explosion
- Sparks can ignite any spilled battery acid, causing chemical burns
- Sparking can damage electrical components in the vehicles
Avoiding these risks is as simple as always connecting positive first and negative last. The few extra seconds it takes is worth it for the safety of yourself and both vehicles.
Step-by-Step Guide to Safely Jump a Car
Here is a step-by-step guide to safely jump a car while avoiding any sparking risks:
- Position the vehicles – The car with the good battery should be parked next to the dead battery car, but not touching. Turn both vehicles all the way off.
- Identify the battery terminals – Locate the positive and negative terminals on each battery. Positive will be marked with a “+” or “POS” and negative with a “-” or “NEG.”
- Connect the positive (red) clamp to the positive terminal on the dead battery – Attach the red jumper cable clamp to the positive terminal on the dead battery first.
- Connect the other end of the positive (red) cable to the positive terminal on the good battery – This will allow electricity to flow from the good battery to the dead battery.
- Connect the negative (black) clamp to the negative terminal on the good battery – Now that the positive cable is attached at both ends, next connect the black negative clamp to the good battery’s negative terminal.
- Connect the other end of the negative (black) cable to a metal ground on the dead car – Finally, attach the other end of the negative cable to a bare metal, unpainted part of the car with the dead battery – such as the chassis, engine block, or frame.
- Start the working vehicle and let it run for a few minutes – This allows the good battery to charge up the dead battery a bit.
- Try to start the car with the dead battery – If it doesn’t start up right away, let the working car keep running and trying cranking again.
- Disconnect cables in reverse order once started – Remove each cable end starting with the negative cables first.
Following this process ensures electricity flows from the good battery to the dead one safely, without risk of sparks by the hydrogen gas. The most important takeaway is to always connect the positive red cable to both batteries first before installing the negative black cable last.
Why the Positive Cable Should Be Connected First
Connecting the positive jumper cable first accomplishes a few important things to ensure safe electricity flow:
- Allows current to flow to the dead battery before the negative is introduced
- Avoids sparking near the battery terminals and any hydrogen gas buildup
- Prevents voltage spikes when the final connection is made
- Establishes initial connection safely away from battery
Here’s a more in-depth look at how leading with the positive cable prevents issues:
Prevents Sparking Near Battery
Sparks are generated any time a new connection is made in a circuit with voltage potential. When jumping a car, the final connection is attaching the negative clamp to the dead battery. If you were to attach the negative clamp first instead, that final connection where sparking occurs would be right at the battery terminal, where hydrogen gas from the dead battery accumulates. Connecting positive first allows any initial sparks to happen safely away from the battery itself.
Avoids Voltage Spikes
If the negative is connected first, the initial connection of the positive lead can create a voltage spike. Spikes could potentially damage vehicle electronics and electrical systems. Connecting positive first and negative last provides a controlled, steady voltage flow rather than an initial spike when the circuit is completed.
Establishes Initial Connection Away from Battery
By attaching the positive clamp to the dead battery first, you’ve created the initial connection needed for current to flow. Any sparks are away from the battery itself. The battery will now have a voltage potential ready for the negative lead to then complete the circuit. There’s no risk of hydrogen ignition at the battery since a connection is already established.
Connecting positive first provides a safe initial flow of electricity before the negative lead completes the circuit. It prevents dangerous sparking where hydrogen gas has accumulated while also avoiding voltage spikes.
Using Ground Instead of Negative Battery Terminal
You may notice that in the jump starting instructions, the final step is to connect the negative cable to a ground on the dead car rather than the negative battery terminal itself. Why is this?
Connecting to a ground rather than the negative terminal offers a few advantages:
- Avoids any sparking right at the battery
- Prevents surge back to the good battery when started
- Allows you to reach a ground further from battery
Here’s some more detail on why using a ground is preferred:
Avoids Sparking at Battery
Even though the positive lead is connected first, there will always be some minor sparking when the final negative connection is made. Using a ground allows this sparking to occur safely away from any hydrogen gas buildup near the battery itself.
Prevents Power Surge When Starting Engine
If the negative cable were connected directly to the dead battery, the initial surge of electricity from the good battery to the dead battery when the engine starts could overload the system. Using a ground avoids electrical overload and prevents damage to the good battery and charging system.
Reach Farther from Battery
Using a ground instead of the negative terminal allows you to make your connection farther away from the battery and any hydrogen gas. You can look for an unpainted metal part of the frame or body safely distant from the battery area.
So while it may seem counterintuitive to not complete the circuit back to the negative terminal, grounding the negative lead offers important advantages for safety and prevention of electrical damage.
What Can Happen if Connected Incorrectly
If the negative jumper cable is connected first instead of the positive, what are some specific things that could go wrong? Here are some consequences of incorrect connection:
- Hydrogen gas explosion – Sparking near the battery could ignite built-up hydrogen gas, causing an explosion.
- Battery acid burns – Sparks near leaking battery acid could cause the acid to spray and burn skin.
- Damage to electrical systems – Voltage spikes could damage onboard computers, sensors, or other electronics.
- Melting jumper cable clamps – Excess heat from sparking could melt the metal jumper cable clamps.
- Fire – Sparks near the battery could ignite flammable materials and cause a fire in the engine bay.
While the odds of any single issue are relatively low, the consequences can be severe. Connecting the positive first and completing the connection at a ground point far from the battery minimizes the risks and prevents damage. It only takes a few extra seconds to do it correctly.
Summary of Why Negative Cable Is Connected Last When Jumping a Car
Here’s a quick summary of the key reasons to connect the positive jumper cable first and negative last:
- Avoids sparking near possible hydrogen gas buildup on dead battery
- Prevents voltage spikes that could damage electrical systems
- Allows initial connection away from the battery terminals themselves
- Reduces risk of surge back to good battery when starting
- Keeps any sparking away from potential leaked battery acid
Taking these simple precautions reduces the chance of explosion, fire, acid burns, or damage to the vehicles. The few extra seconds needed to follow this order makes the process much safer.
Tips for Properly Jump Starting a Vehicle
Here are some important tips to keep in mind beyond simply connecting the cables in the right order:
- Wear protective gloves and eyewear in case of battery acid or sparks.
- Turn off both vehicles before connecting cables.
- Verify the good battery has 12+ volts.
- Clean any corrosion from the battery terminals.
- Position the vehicles close but not touching.
- Avoid leaning over the batteries as you make connections.
- Try to start the car within a few minutes to avoid draining good battery.
- Let the revived car run for several minutes before disconnecting cables.
- Disconnect cables carefully in reverse order.
Taking basic safety precautions, confirming adequate voltage in the good battery, and following the proper connection order will allow you to get the dead car started while avoiding damage or injuries.
Frequently Asked Questions
Can you connect the negative cable to the dead battery when jumping a car?
It’s not recommended. Connecting the negative cable to the dead battery can cause dangerous sparking right at the battery terminal. It’s safer to attach the negative clamp to a ground point on the chassis or engine block instead.
What happens if you connect positive first when jumping a car?
Connecting positive first allows current to flow to the dead battery before the negative lead is introduced. This prevents sparking near the battery and voltage spikes that could damage systems. It establishes a connection away from hydrogen gas.
Can you connect the negative cable to the negative terminal on the good battery?
Yes, you can connect the negative cable to the negative terminal on the good battery once the positive lead is attached at both ends. This will complete the circuit safely. Just avoid connecting the negative lead first.
What happens if you connect the jumper cables backwards?
If the jumper cables are connected backwards (positive to negative terminals), it won’t work to jump start the vehicle. At best it simply won’t start the engine. At worst, it could cause damage to electrical systems, overheat the cables, or cause sparks and fires.
Can you touch the positive and negative cable together when jumping a car?
You should never allow the positive and negative clamps or cables to touch each other when jump starting a vehicle. Doing so completes the circuit immediately and will create dangerous sparking and shorts. It could seriously damage the charging system of the good battery.
Key Takeaways on Jumper Cable Connection Order
- Always connect the positive red cable first to avoid sparking near the dead battery.
- Attach the negative black cable last after the positive lead is secured.
- Connect the negative clamp to a ground point on the chassis, not the battery terminal.
- Following this order prevents fires, explosions, acid burns and electrical damage.
- Use ground instead of negative terminal to further avoid sparking at battery.
By taking a few simple precautions and connecting jumper cables in the proper sequence, you can safely jump start a dead battery and get back on the road. Be patient, avoid shortcuts, and don’t take risks – connecting positive first and negative last will prevent problems and get you on your way.