nubimax wrote:
My meter shows that the ground wire is broken so it should not be doing anything.
We are talking about the ground wire in the cable between the wall socket and the computer here, aren't we?
Also, the wire is apparently broken now, but wasn't necessarily always broken. I am assuming it was not broken until the computer started playing up, and it being broken is possibly the cause of the problem.
I had the following paragraph at the end. The text has got so long, however, that I decided to put the "summing up" at the start:
Suffice to say that the ground and the common in your socket in the wall are almost certainly connected somewhere in the house. This means, if the common and the ground connector are swapped in the device (in this case your computer), the device will find the "common" connection via the ground wire. If the ground wire in the cable being used then breaks, the device will stop working (obviously).
And now the long-winded explanation:
There is not really a big difference in how to wire DC and AC. Because a lot of the stuff that "normal people" as DC see is 12 V in cars, or 24 V in trucks, the wires are often a little thicker than for the AC applications that normal people encounter. This is because, to get the same work done, i.e. power (Watt), you need a higher current (Ampere) when the voltage is lower, and that needs a thicker cable.
Otherwise, the principle is the same: volts applied to one side of the device cause a current to flow through the device and work to be done. For that, you only need two wires. One to the device from the source, and one back to the source from the device.
In DC circuits the wires are referred to as "plus" and "minus". In AC they get called things like "hot" and "common", "hot" and "cold" or whatever.
The principle is always the same: the "hot" wire applies the potential (Volts), and the "common" is the way back to the source.
The ground has nothing to do with the operation of the device. It is purely a safety feature, providing a "way of least resistance" back to ground should the volts get onto a part of the device where they shouldn't be, like the housing, for instance.
The "way of least resistance" means, hopefully, the stray volts will go that way to earth (and hopefully trip a fuse) rather than through a person that touches the part of the device where the stray volts are.
Generally, the ground is connected to the housing and metallic chassis parts of the device, but mostly not the operational circuit in the device. There are exceptions, for instance professional audio gear mostly does have a connection between signal common and earth.
Wiring up a boat or whatever is relatively simple in as much as you see the entire circuit: starting at the plus pole of the battery, a wire goes to the device (with probably a switch on the way, and a fuse maybe) and from the other side of the device a wire goes back to the minus pole of the battery.
In principle, an AC circuit is the same. Volts come into the house from the power plant, go through the devices (and fuses and switches) and flow (theoretically) back to the power plant. Two wires. The only difference really, is that the potential (Volts) in the "hot" wire changes polarity regularly (60 Hz in USA, I believe). Therefore, the current in the circuit changes direction at the same frequency, hence "alternating current".
The third wire in your plug is the ground, which, as I said, is simply a safety feature that has nothing to do with the operational circuit of the device.
What you don't see, unless you wire your house up yourself from scratch, is that the common and the ground are generally joined at the fuse box of the house, and connected to a stake in the ground. The wiring from the power plant is, as far as I know, only the "hot" side of the circuit.
The "common" is present in the wiring in the house, but generally not in the power distribution network. The power lines you see along the sides of the road are only "hot" wires. There are usually three because power is generated and distributed as "3 phase power". In that system, the "common" is provided for each phase by the other two phases.
Wikipedia
The "common" is literally connected to the earth, i.e. a big fat metal stake in the ground, at the power plant and at the house. If I understand it correctly, no real current flows. It is more like an anchor, so that the Volts have a stable reference that they want to flow back to.
So, once again, the summing up:
Suffice to say that the ground and the common in your socket in the wall are almost certainly connected somewhere in the house. This means, if the common and the ground connector are swapped in the device (in this case your computer), the device will find the "common" connection via the ground wire. If the ground wire in the cable being used then breaks, the device will stop working (obviously).