How would dropping/touching engine or other metal parts affect electrics with a disconnected positive lead.

Surely if earth is connected to battery and pos is disconnected no current can flow even if it touches metal??

MVS wrote:

How would dropping/touching engine or other metal parts affect electrics with a disconnected positive lead.

Surely if earth is connected to battery and pos is disconnected no current can flow even if it touches metal??

It was so much simpler in my day, bring back points and filament bulbs, at least you knew where you stood with them

The battery has approximately a 12v "potential difference" between its positive and negative lead and, due to the construction of the battery, it is able to deliver extremely high currents (around 300A to start the car for example). Your car battery is capable of delivering around 2.7KW (KILOWATTS!)for a short time so the potential for excitement and heat are large. It can't electrocute you in the acknowledged sense as the volts are too low, but it can and will produce enormous heat if connected in a way which shorts the two terminals together.

Now to the crux..... you will only get a big bang if you connect the two terminals together. So if you leave the negative lead connected and, whilst disconnecting the red positive lead, your spanner happens to touch the chassis while its other end is around the bolt on the positive, you will have connected the two terminals together through your spanner and it will become a permanent part of your chassis as 300 amps flow through it and weld it to the car! You will also probably let go of it very smartly as its temperature reaches that of the Sun!!

Conversely, if you disconnect the negative lead first, thus also disconnecting the chassis from having anything to do with the battery, then your spanner can be round the positive and touch the chassis with no ill effects. I would suggest that, once you have disconnected the battery negative, you close the protective cap on it so that nothing metal can accidentally fall across the two terminals. There is no need to disconnect the positive terminal of the battery unless of course you are taking the battery out for some reason. If you do undo both, always remember, UNDO THE NEGATIVE FIRST AND RECONNECT THE NEGATIVE LAST. When you have undone the negative lead, tuck it safely out of the way so that it can't suddenly spring back and touch the negative of the battery again before the work is finished.