General newbie question

[Flared69]

When I read of people wanting to do something that has anything to do with electrical parts in cars, the gauges etc, I hear people say "disconnect the negative terminal".

Is there any reason why its always the negative terminal? I have a kill switch on my battery which I think is on the negative (but I have to look at it when it gets back from the shop), I use that all the time, but is there any reason why its the -ve and no the +ve? Just for peace of mind really .

 

[AKRAY4PLAY]

electricity flows - to +. so if you disconnect the ground lead, and your doing something that will cause a short. the flow of electrons is not through your car. but it does not really matter, with either terminal disconnected there is no potential for electron flow. most of the time other leads are hooked to the + terminal, so killing the - terminal is usually easier.

 

[billagroom]

You will get sparking when you disconect and reconect the + no sparks fron the- side so most people do it that way unless they like the light show.

 

[gooney0]

YES

The reason you disconnect the - terminal is....

Relays, coils, and capasitors can hold a charge for a long time. Disconnecting the positve terminal won't prevent a short. Disconnecting the negative terminal will as the car will no longer be ground.


99.9% it would make no difference though.

-Gööney0

 

[Flared69]

thanks guys, great to know

 

[JohnZ]

Disconnecting the (-) cable eliminates entirely the ground path back to the battery, which makes it impossible to create a short anywhere in the car - nothing is ground.

 

[cwerve74]

I see the issues as saftey. When you put a tool on the positive side of the battery and accidently bump the tool into a metal part on the car you get a high current short. Lot of spraks, chance of fire and battery explosion. Since the negative side is the same as the metal frame you do not have that risk with a tool on the negative side of the battery. --- So when you want to get the power out of the car to work on electrical stuff and you are going to disconnect the battery. DISCONNECT THE NEGATIVE SIDE FIRST. No chance accidential short when doing that task.

 

[cntrhub]

Aussie,
All above comments are worth repeating here. But instead, think in terms like this: NEG - OFF FIRST..... for electrical repair or battery replacement. NEG - ON LAST when installing a battery or electrical work is completed.

 

[Flared69]

Oh I figured that

I have logic, just want more knowledge

 

[Mac]

Oh I figured that

I have logic, just want more knowledge

Here's another way to think of it which I've found helpful in explaining this.

The negative is 'common' throughout the vehicle; the frame, the engine block, every major componant is tied to the negative. Metal cars use the body itself as a conductor. In our fibreglass cars, there are quite a number of "ground straps" which serve to bring all of the major componants to ground.

On the other hand, each positive circuit is independent, passing through a fuse (okay, not strictly true but close enough for this explanation).

Electricity moves at the speed of light and it seeks any and all paths but it needs to have a complete path to flow. By removing the negative, you've made it the entire car safe by eliminating the possibility of a complete path.