Pants shitting moment (got zapped changing plugs, now it wont start)

No harm

 

Just to clear up the electrical situation....

Cars do not have ground.
Period.

What you have are negatively and positively charged conductors.

"Ground" is called "Ground", because it is electrically connected to the dirt that you walk on. The GROUND. Where the concept of ground becomes relevant is in long distance power transmission. Specifically, alternating current. By using the ground as one side of the circuit, you reduce the amount of wire it takes to transmit electricity by 50%.

In alternating current, they only need to send out one wire. On this single wire, electrons are pulled back and forth 60 times per second (60 Hz). We call the push phase "negative", and the pull phase "positive". At the null phase, when the electrons are stationary, the voltage is zero.

But the thing about voltage, is that it is always RELATIVE. So what do I mean by the voltage being "zero" at null? I mean that the voltage is zero relative to GROUND. It is established zero relative to ground at the point of transmission, and it is re-synchronized relative to ground at the transformer where it is split into "live" and "neutral" lines, and then finally, it is again synchronized to ground in the electric distribution panel.

So when you're wiring an alternating current circuit, you are working with a "live" alternating voltage conductor, and you are working with a "neutral" or "ground" conductor to complete the circuit.


Automotive power is direct current. That means that the electrons flow in one direction only, from the negative terminal into the positive terminal. Some people get a little bit confused by this point, that the actual substance of electricity flows from the negative terminal. Unfortunately, the terminals were named positive and negative before the discovery of the electron, hence the confusion and use of terms like "electrical current" which is said to be in the opposite direction from "electron flow".

Now whether a vehicle is wired chassis-negative or chassis-positive, really doesn't matter, specifically because we are not dealing with ground. We are only dealing with the relative voltage between the terminals. The very state of naming of the terminals proves, in fact, that there is no relevance. If the electron was discovered before the terminals were named, what is called the "negative" terminal would probably have been called "positive".

In a chassis-negative vehicle, you can imagine that there are electrons everywhere in the chassis trying to blast out through everything in order to get to the positive terminal. Seems kind of strange when you think of it like that, doesn't it?

The only thing that really makes a chassis-positive vehicle seem "not right" is the fact that it is not in compliance with standard practices. It doesn't make any difference relative to ground. You know, that flat thing the vehicle rolls on.


Now where the confusion in "negative" vs "ground" terminology comes from, is in powering DC appliances on AC circuits. In an AC circuit, we consider the ground to be a constant voltage, and the live to be a voltage varying about ground. DC is obviously constant, so where better to begin a DC circuit than from ground?

So you have your first constant. Now you only need an additional constant with a voltage differential from there. We use some form of 1-way electron gate to filter out the negative phase of the AC line, leaving only the positive phase, now electrons will only flow in one direction. The most common semi-conductor solution to this is a device called a diode. It allows electrons to flow only in one direction. Throw in a capacitor (like a small battery), and a resistor (reduce the rate of electron flow), and you have yourself a DC power supply, with your positive terminal relative to your negative terminal (which also happens to be ground). A more sophisticated conversion device is called a "rectifier". These devices are also able to take the negative phase of the alternating current and convert it into a positive. You can think of it like a reverse gear in a transmission, but for electrons.

Now BamaToy1997 suggested disconnecting the negative terminal of a battery in order to ensure that you don't short anything out. In order to short anything out, you need to have an electrical connection between the positive and negative terminals. Because the vehicle is chassis negative, the entire positive electrical circuit is insulated against shorting out against the uninsulated, negatively charged chassis. If you disconnect the positive terminal, then you can short it out by touching ANYTHING to that positive terminal. If you disconnect the negative terminal, you would have to short out some part of the positive circuit to the negative terminal. Of course, the positive circuit is fully insulated, so the only thing you could do to short the battery out is to create a direct bridge from the negative terminal to the positive terminal.

When the negative terminal is disconnected from the battery, the entire chassis takes on the positive charge relative to the negative terminal of the battery, however, unlike being a big thick wire running directly from the terminal to the chassis, this voltage is filtered through a number of very high resistance circuits. If you touch that now positively charged chassis to the negative terminal of the battery, you will still be creating a short. In this short, the current will be FAR lower, so there won't be any big sparks. The good news is, of course, that as soon as you contact that negative terminal to any part of the chassis, you are just re-exerting the negative potential where it is intended to be under normal circumstances.

So there will be some electron flow, in the proper direction as intended, and without the dramatics or potential for damaging the battery.

When servicing electrical components, disconnect the NEGATIVE terminal.

And cars do not have ground, even if the term is commonly used to mean negative -- they truly are not the same thing.

 

would of still been grounded by the plug.

 

No.
Ground does not exist.
Negative is disconnected from the terminal.
Plug itself will be charged positively as soon as it is disconnected from the negative terminal.

 

Back to the pants, something like that will get your heart jumping pretty good. I was in a hurry and hooked up some jumper cables one time but forgot to make sure the other ends were not touching together. You get to witness the full "Cold Cranking Amps" out of your battery in action.

 

I'm guessing you missed all the posts following the comment you quoted...

 

Shesh!! Shep, you really do have to get technical....lol. I did know the information that you have mentioned. HOWEVER, in the world of automobiles the general common nomenclature does still call the negative terminal "Ground". Even in the repair manuals written by the engineers and the like still call it a ground. No, TECHNICALLY it is not a ground, as you have explained, but to all us techs out here, we still call it ground or negative terminal interchangeably.

 

To simplify this thread:

Remove the negative cable from the terminal of the battery BEFORE messing with electronics.

These damn pesky newer vehicles can shit the bed real quick (usually the BCM or worse depending on make) if you send power where it doesnt belong.

I personally dont remove the cable to do plugs, but just my preference, been turning wrenches for over 25 years, and welding using the battery is not recommended (unless you have one of those power pack welder thingys, lol)

Carry on.

Oh and also I would like to PM the OP my address so he can send me that fried torque wrench, its junk, just send it over..