Isnt ground supposed to be 0

[Lofixx]

As most of us already know the ground is connected to the case of the psu and when the psu comes in contact with the computer case it grounds the case. The ground wire in DC is 0(neutral) and below it is negative and above it is positive. I have a fanbus in my case and I was hooking up my new led fan I put the positive in the positive clip, but I forgot to put the negative in and when I turned my computer on the fan was spinning but I noticed that the negative was not clipped in. I thought that maybe a negative somewhere in the case was not properly insulated and was touching the case I checked everywhere for it but nope everything was insulated. After learning this I went to my sister's computer and tried to emulate the same thing again so i just put the positive in the molex and the negative on the case; guess what the fan spins. Now I thought something might be up with the ground in my house so I tried the same thing in my computer engineering class at school and the fan still spins. All my life I thought that ground was neutral or was I wrong.

Can anyone explain this?

 

[CTho9305]

in general, ground is 0. so are the black wires in power connectors. the ground in the power supply usually is also hooked up to the case - that way if something shorts power into the case, the ground connection prevents you from getting electrocuted if you touch the case. when you put a fan from a +5 or +12 to the case, it is the same as to the negative connection.

 

[Geniere]

The DC ground is really termed DC common. It may or may not be connected to ground, depending on the design engineer?s requirements, although I believe all PC?s are as you describe. The grounding conductor in the AC line cord is required by the electric code for the sole purpose of safety. Should a fault occur, it would keep exposed conductive surfaces at ground potential or cause the circuit breaker to blow. Ignoring the safety issue, a well-designed PC should work just as well with or without the case being grounded.

Regards

 

[RossGr]

I am very unclear on just how you are connecting your fans. If by negative, you mean a black wire, generally this is ground, it will be negative wrt to the other wire, but is intended to be connected to ground. So if you are grounding the wire then the system is behaving exactly as I would expect it to behave. If you are not connecting the black wire to anything, then it is more of a mystery, unless your fan is somehow connected to ground through the fan bus.


Is the black wire you are not connecting attatched to the fan or the fan bus? You need to specify the wiring of this system a little better before anyone can explain to you what is happening.

 

[ScottMac]

"Ground" is just an expression of reference. "Ground" can be any voltage. If "Ground" is not "Ground," then there is a "Phantom Voltage" between "zero" and the reference referred to as "common" or ground.

Token Ring had three phantom voltages, depending on which two leads you were measuring against.

Even "Earth ground" is not necessarily a stable value. If you drive two stakes in the Earth some distance apart and hook up a meter, chances are very good that there'll be some potential between the two. That is why it can be dangerous to use copper to connect two locations without some sort of entrance protection.

A voltage measurement is useless without some specific reference; the norm is to reference against the common connection in the circuit providing the power. If that reference also happens to be neutral, or Earth, then all the better.

FWIW

Scott

 

[dkozloski]

Whole carreers have been built around studying the grounding of electrical power and electronic signals. ScottMac hit on the basic problem. If you have power, signal, and safety ground circuits interconnected haphazardly you will soon find that in very low resistance circuits you can develope heavy currents with just a slight difference in potential. These circulating currents are called ground loops. The result will be 60~ hum and noise riding on low level signal circuits resulting in erratic operation and unreliable data. In gross cases entire power grids can be brought down by the differences in ground potential as a result of sunspot activity. In fact at several northern latitude universities the possible extraction of useful power is being explored.