? Ground Wires on Molex Connector (Reverseable?)

Synetech

Hi,

Is there a difference between the two black ground wires on a drive
connector? For example, does one ground the 12v and the other ground
the 5v or do they both go to the same place? Is it bad if they are
reversed?


Thanks a lot.

__________________
--
Synetech

Grace

All ground wires are ground wires. Reversed or not, it won't make any difference.

Synetech

Well that's not entirely true. A ground wire for an oven receptical is not exactly equal to a ground wire for a bookmark light. I'm guessing that you meant in a computer though, but even then, there are different kinds of ground wires in a computer and I doubt that they can be mixed and matched arbitrarilly.

__________________
--
Synetech

Judas

while i can't claim any electric or psu knowledge at all really in this area.
synetech, you are right,

There are the grounds which just are a means for the positive to run through to negative being the ground, and then there is the positive to negative, and positive to negative supplemented with a ground.

Now in the DC world inside the machine, i'd suspect that most likely on a standard 4 pin molex, that either ground, would be able to be flipped around without worry. But i'm not sure about any of the others.

I've always been confused by the -5v and -12v rails that are marked on PSUs. Which by somewhat thinking about it, would seem that there would be wires that would be required to connect in the right way.

No? Not sure, where's a resident computer PSU expert when you need on... i'll post a link to this thread in the OCZ Support forum, perhaps one of them may have an answer for us.

__________________

MIG-31

considering grace did not make any resemblance or remark to any oven or lighting system of any type..... the answer was given to the question you asked.(but you're point is understandable).

Of course she meant in computer (molex) terms.....the is no difference as far as i know (but i'm not 100% + on that)

besides that if the was any difference in the black ground wires it would simply be pointless having the same colour coded cable,surely these would be a seperate colour also.

__________________

Judas

Mig, i've come across some PSU's where one black and one black with a white stripe are clearly visiable, making it clear that there "is" a difference? i haven't a clue though yet.

Haven't found anything on the net either, other then when chaning molexes or anything of the sort, to put everything back in the same position (making sure each is labled as clearly as possible)..

__________________

H3X4D3C1M4L

Its all in the return to the neutral circuit of the AC plug.

It doesn't technically matter in most power supplies but in some older power supplies it did matter for purposes of eletrical noise and interference.

MIG-31

Judas all im going by is from what i have seen in the past,i personally have not had a single psu with any marking on one of the black ground cables and i have had a few in the past..I'm not tech minded like a huge number of the members here and i only said a small opinion on what i thought.... i also said i was not positive on the answer...but thanks for pointing it out.

even i flick through Wikipedia does not show the answer required.

__________________

Judas

yeah.. it's an interesting question non the less....

__________________

Grace

We are talking about computer power supply units here, and even in your example the ground wires are the same. The latter is just not large enough to withstand the current of the oven, so it will probably get burned.

Especially in DC circuits, all ground/neutral cables are exactly the same. They just pass the voltage to the ground cable of the AC plug. You can match any voltage line to any ground wire as long as the cables are strong enough to withstand the current, which is not really a variable when talking about computer PSUs. Many PSUs actually gather all those small black cables in the casing and solder them into one ground point. As you can guess, since all cables originate from the same source, they do the exact same thing. And ground wires always do the exact same thing. I even have several MOLEX adapters here for various uses which I modified and have both ground wires soldered together instead of two separate wires on the female plug, so both the +5V and +12V are using a single ground wire of a given MOLEX.

All ground wires are the return lines of a voltage to the ground or the neutral/ground wire of the AC plug. There is nothing different about them and they do nothing more than what they are supposed to. They hardly ever matter about (only in high voltage industrial lines) or cause noise, ripple or anything else. It's simple electrics.

Think of the ground wire as an infinite 0 voltage line where you can plug any other voltage line at it to work. That's the simplest way to understand it. If that doesn't work, there are many alternatives like teachers, books and such. You shouldn't be making a fuss about something so simple. You can always use any ground wire for any power line, as long as it is strong enough to handle the power which will move through it.


PS. I have seen tens of hundreds of power supply units but I haven't ever seen a PSU with two different ground lines, and that technically sounds impossible as there is only one ground wire at the AC plug. If you can remember the manufacturer of that PSU, please let me know, I'd like to get one and check it out myself.

Judas

i wasn't refering to the AC plug... that's just a standard 3 pin plug.

i'm talking about the 2 black wires for a 4 pin molex that say connects to the cd-rom drive...

I've seen some with black, one of which has a different color or white stripe. Perhaps for manufacturers own references? haven't a clue... i'll have to dig through a few things and see, but i beleive it was in a dell machine i had come across that.

__________________

Grace

I didn't say otherwise. I said it's impossible to have two different ground points in a PSU when the AC plug has one to offer. They will end up to one ground point anyway.

I just want to know which ones are those with the white stripe or different colors. As I said previously, I've seen thousands of power supply units and none had different ground wires. If you remember which manufacturer/model that was, I would like to know in order to ask them myself.

I have seen Dell reference power supply units, they were pretty normal.

Judas

yeah... all the dells i've seen have had normal ones... which leads me to beleive that this psu i had found was not a typical dell psu (even though most of the dell psu are non standard size)....

If i can find it again i'll post it.

__________________

PangingJr

not sure if this helps answering any of the questions.

below information, which is stated in the DC output / Grounding section of the EPS12V power supply design guide (don't see this information in the ATX12V ones).

"The ground of the pins of the power supply wire harness provides the power return path.
The wire harness ground pins shall be connected to safety ground (power supply enclosure)."

Synetech

That's what I was hoping for. Someone else said the same thing earlier today and I said that it begs the question why there's two then.

It's not necessarily just high-voltage that would make a difference; you could burn out a microscopic ground wire (like the kind in a die) on even a fan (probably even an LED).

You've probably already seen it but this site has a lot of details on power connectors.


Anyway, thanks for the input everyone; I just wanted some peace of mind that I wouldn't fry my drives. I have to replace the PSU eventually anyway. In fact that's why I removed the plastic from the connectors today, to add some solder to support the connections because my drives have been intermittently clicking off and on for a while and it's driving me nuts. Some of the wires in there were a bit frayed (I guess I manhandled them a bit too much) so the power wasn't getting to them properly. My optical drives have the same problem which is why I want to change the sucky PSU—it came with the case. I figured I'd get off my butt and take care of it once and for all before any permanent damage is done to the drives. They've been good all day but I'll have to test them tomorrow by wiggling the wires while the system's on.

__________________
--
Synetech

Grace

The MOLEX is a pretty old design. There are two of them because each cable can withstand a given current and power, not infinite. If both voltage lines are connected to a single ground wire, that ground wire has to withstand the power and current of both those two voltage lines. It was designed like this for safety reasons mostly, since earlier units had wires which were working pretty close to specification limits. Today, an average PSU copper wire can withstand 3 to 30 times the maximum power and current a component can draw (with the worst case being a 150W+ CPU taking power from two 12V wires, 4-pin 12V Intel spec connector, that's 75W per line, the wire can withstand about 200W).

Of course even today the manufacturers have to follow specifications, so the maximum current of a single 12V wire is set to be 12A. The wire itself however can handle at least 18-20A. It is all about safety precautions.

Of course you could. If you have that fan cable ground more than 100-150W of power, it will most probably get burned. But a single fan ground wire can be used for up to like...6-10 fans. The voltage is irrelevant, the current is what we actually care about. You can have 20.000V with 0.00001A current, that's a minimal amount of power.

Synetech

It's interesting you would mention that because just the other day I was reading an article in a trade paper about how desktop computers have plateaued and are moving forward very slowly compared to other types of consumer electronics.


I said a wire on a die—those microscopic filaments in a CPU—not a fan ground wire. I don't have the numbers but I'm sure that a motor could burn one of those.

__________________
--
Synetech

Grace

True, I misread, you said 'on even a fan' and I read 'or even a fan'.

Actually, pipelines can take quite an amount of power, depending on their use and design of course. Remember, most of the power inside a PSU is transfered between the components via pipelines before it actually reach the cables.

Matth

The two ground wires in a molex, most likely end up connected to the same ground point in the PSU and the same ground PCB land on the drive.

As for the -V lines, the only place they go to is the ATX power connector, and on modern boards, they don't do much. Back in the old days, the 640k of D-RAM ("enough for anyone") may have been a type which needed negative voltages as well as positive, but now very few parts (if any) would require negative supplies - serial ports, if not equipped with a voltage converter.

__________________
Mary had a little lamb,
Her father shot it dead
Now Mary takes her lamb to school,
Between two crusts of bread

H3X4D3C1M4L

ATX 1.3 abolished most negative rails, including the legacy ISA -5V rail.

BTW Grace you said the ground in a DC circuit passed the potential difference to the ground plug of the AC circuit... which isn't true, in PC PSU's it goes to the neutral side (at least in North America where its 120V hot and then the neutral and then the ground), if it was passing that to the ground you'd have an overloaded ground line and not enough return current on the netural side.

Grace

Sorry, kind of a habit, when studying electrics and especially AC networks and DC systems, neutral and ground are the same thing. No voltage line in any household application or even most industrial ones are truly going back to the ground, it would instantly blow up that line since that's a short-circuit! They all end up to the neutral line and the true ground is present for safety purposes.

H3X4D3C1M4L

Absolutely correct

swimtech

This was quite an interesting thread...

The answer to the original question is no, as Grace intoned, and you can reverse them with no ill effects. In fact, if you were to unplug the computer (for safety's sake...) and check the resistance between any two molex black ground wires, the resistance would be very close to zero - indicative that they are tied back to a single point. In other words, the ground "reference" is the same. However, if you measure the resistance from any black wire to the metal parts of your computer case you should measure an open (infinite resistance) circuit - it gets interesting (but not too complicated...) from here...

You have to be very careful in comparing "grounds" when dealing with power supplies though (especially with respect to the world outside the case of the PSU), because "ground" is relative - not absolute. In a computer for example, there are actually three "ground" references:

1) Earth ground - the semicircular hole on a three prong outlet plug that generally grounds the power supply metallic case to the earth outside your house. Yes, your main house circuit is connected to earth ground, but indirectly a little. At the breaker box where electric service enters your home, the neutral leads from throughout the AC outlets of your home are generally connected to a bar inside the circuit box, then from there to a stake driven into the earth nearby - as is your phone and cable (for TV or such...). The neutral is tied to it with a relatively small wire because there is almost no current on it - it doesn't need to carry much (if the house is wired properly) - just the leakage current due mainly to the difference in distance (and therefore resistance) of the wires according to how they're installed throughout walls of your house. This is generally done to prevent shocks (or tingles...) from occurring if you were to touch an exposed metal part of your computer case and another earth ground in your room.

2) Hot ground - this is an electrical term for the "ground" created where the two anodes of the diodes of a wheatstone bridge (an arrangement of four diodes that starts the process of converting AC sine wave voltage into what will become DC voltage for use by an electronic device) meet. That "hot" ground created by the diode bridge circuit is actually about 70 volts AC with respect to the neutral lug of an AC plug connector. If you were to touch that point and then touch earth ground or the neutral on your AC plug connector (possible if components are exposed...) it could KILL you. That 70 volt difference is only limited by either the fuse in the device or by the 15 to 20 amp breaker in the breaker box of your house. This has happened to me once - ONCE - by mistake, and it knocked me to the ground, blew the fuse, and shorted the diodes! Called hot, because with respect to outside world - it is! I laugh now...

One last edit: have to add this - any electronic device that plugs into the wall has to have some circuit that changes the AC in your house to DC that the device can actually run on. Therefore, it likely has a "ground" like this - hence the reason for all those "Hazardous Voltage!!!" warnings you see on stuff.

3) Cold ground - this is an electrical term for the "ground" referenced by the regulated (and isolated...) DC voltages used in an electronic device. In modern electronic devices, especially those using switched mode power supplies (such as computers, TVs, and VCRs to name a few...) the regulated DC "side" of the circuit is isolated from the AC conversion to sawtooth DC "side" by a transformer - no physical electrical contact at all - the transferrence of energy is accomplished magnetically (this gets complex - too much for this post...), and feedback to the regulator (load balancing...) happens through an optical/semiconductor circuit (an optoisolator circuit generally). Cold ground and Neutral ground in a device can be at the same electrical potential, but often are not due to design considerations (the list of which is very long). Again, if the differing grounds are connected somehow AND have a different electrical potential something generally blows up, or smokes, or burns, or tingles, or hurts, or dies. The energy is not wasted - stuff happens...

Again, those black molex wires are the same "ground" potential - just keep them inside the case, and connect them only one to another because that's how they were designed to be.

__________________
It's not so much getting your way that matters or not - what matters is how you go about getting it.

H3X4D3C1M4L

Now now no need to show off

All true though... I've had many dealings with electricity. You think that 70V zap was bad? I know an electrician on a railway line and he saw what happened to someone touching a screw that dropped on a 600V charged wire.... knocked to the ground? No, violently thrown back and his arm's skin peeled all the way back....