I have disconnected and reconnected my battery terminals several times over the years. While I am careful not to get the wires crossed or touch each other, I have never thought about what order I do that.
Is there a correct order for disconnecting and reconnecting the positive and negative terminals of batteries? And why is it important? LMK
You should always remove the negative terminal first when disconnecting and replace the positive terminal first when reconnecting. Then nothing “shocking” is likely to happen.
If you do it the other way around, it has to be done with special care or you could have the role of a bright spark in a drama called “The Accidental Welder” and give your nervous system a 300 Amp surprise (which it will share with important things like your muscles, your heart and your brain).
It will feel as though someone has hammered a nail into your fingertips. Don’t ask me how I know.
Why this sequence? The battery’s earth (negative) terminal is connected directly to the car’s body...and thus anything else metallic that is bolted to it.
So, if it is still connected when you put a spanner to the live (positive) terminal, if the metal spanner simultaneously touches anything else, it could cause a direct short-circuit to the negative terminal, via the body. The same as if you had laid the spanner directly across both terminals.
At such accidental touch, the battery will try to unload all its (considerable!) power through the spanner you are holding!
Batteries contain a hefty dose of “potential” power. To understand what “potential” means, think of batteries like a loaded machinegun, capable of unleashing a hail of lethal bullets, but mostly doing nothing at all...until somebody pulls the trigger
In the same way, batteries have all the ingredients to unleash streaming bolts of electricity but do nothing at all...until you pull their trigger. In batteries, that trigger is flipping a switch, which completes an electrical circuit between the negative and positive terminals, through whatever electrical motor or instrument you have just turned on.
This kick-starts a chemical reaction between the lead plates and dilute acid in the battery and (chemically) generates electricity. The vigour of the (instant) chemical action and the quantity of electricity sent round the circuit is determined by the device that has been turned on. A tail-light about 1 Amp, a headlight about 7 Amps, a starter motor... up to 300 Amps!
Because the flow of electricity is sent to and through an electrical gadget, the force and quantity of flow are restricted to that instrument’s demand/need through what might be called a “long/complete” circuit (through an electrical device).
If, for whatever reason and by whatever means, the negative and positive terminals are directly joined together it will cause a “short” circuit.
Direct connection between positive is no longer limited to the capacity of a device. The result will be an instant welding machine! Hot enough to melt metal...which you are holding.
You can remove the positive quite peacefully while the earth is still connected, as long as the end of the spanner touching the positive terminal nut does not touch any other part of the car made of metal. Disconnecting and reconnecting in the right order is like putting the “safety catch” on before handling a machine gun.
