# PSU Wiring - neutral/earth?



## scaminatrix (Feb 16, 2012)

Hi all, I've got a mate on teamspeak with me that is telling me that all black wires on a PSU are not actually earths; he says they are neutral. He's a trained electrician and I'm a relatively simple man, so I don't understand most of the lingo.

Can anyone put it in a way that I could understand please? Every single PSU guide I've dug up says that the black wires on the PSU (particularly molex) are earths so are they earths or neutrals? I think he's going to try some ghetto modding and I don't want him to electrocute himself 

Thanks guys


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## silkstone (Feb 16, 2012)

I believe that the earth and neutral are usually hooked up to the same ground. Not sure tho, just something i read a while ago.

http://en.wikipedia.org/wiki/Ground_and_neutral

Edit - From what i remember, the ground is usually connected to the metal part of the enclosure, to short the fuse if there is a fault. Neutral is where the current from the live wire flows... so yes, he is right. The only difference is the function.


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## Batou1986 (Feb 16, 2012)

I think where your both getting confused is AC vs DC terminology. 
AC power has Line, Neutral, Ground.
DC power has Positive, Negative/Ground are the same.


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## lilhasselhoffer (Feb 16, 2012)

The reality here is a might bit different than you are understanding.


Green is a universal color for ground, but ground is not the same as return.  

DC also works differently than AC.  AC requires a complete loop, as current direction changes.  DC requires a high potential, resistance, and low potential.


In simpler terms, DC can use ground in the same way that it uses return (black and green).  AC cannot do this (return must complete the circuit).  So the electrician is trying to communicate that ground (green) is not the same as return (black); this is true, but your comment that ground can be used as return is accurate (assuming that the ground can dissipate the voltage fast enough.


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## silkstone (Feb 16, 2012)

Batou1986 said:


> I think where your both getting confused is AC vs DC terminology.
> AC power has Line, Neutral, Ground.
> DC power has Positive, Negative/Ground are the same.



Not getting confused. The purpose of ground on an AC system is the ground the metal part of a case. The ground wire goes from the mains to the casing, if that. some things have double insulation and no ground.

irc ground and neutral are linked to the same earth... kind of... usually neutral is earthed back at the transformer, where ground in linked inside the house.

It's a bit more complicated than that as there are devices which regulate the charge on the neutral line.. i forget how exactly.

The terminology is actually quite amusing, as before they new exactly what electricity was, it was defined. The negative terminal in a DC system is actually positively charged while the positive terminal negatively charged.

Edit - I see what you mean, the output of the PSU is DC, so it should be called the positive and negative terminal. in respect to terminology, yea.. getting confused  but what you kinda know what i meant? 

Does the negative terminal of a DC system actually link to the ground or is it linked to neutral? (assuming it's not a circuit with a cell)


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## Norton (Feb 16, 2012)

lilhasselhoffer said:


> The reality here is a might bit different than you are understanding.
> 
> 
> Green is a universal color for ground, but ground is not the same as return.
> ...




+1 

DC side of a PSU is different than the AC side.... don't mess with either unless you really know what you are doing. 
On AC (in the US anyway)- 120volt single phase has 3 wires (green, white, and black) green is always ground.
On DC side- check the wiring diagrams for your PSU and PC as there are many different wirings and voltages in there. As far as color.... be careful with that too, 
Example- On a NZXT modular PSU all of the wires are black


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## Arctucas (Feb 16, 2012)

For an ATX PSU, I believe the proper term for the black conductors is COMMON.


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## St.Alia-Of-The-Knife (Feb 16, 2012)

isnt ac ground is the center tap of the transformer?
and your black wire is whats connected to the third hole on your wall plug, so pretty much the same as the ac ground


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## Uncorruptable (Apr 24, 2012)

Hi Everybody,

Just picking this thread back up briefly, if i want to power a device that is max 3.9v, based on all of the above, can i utilise the orange 3.3v from a power supply & hook the orange to live & black to neutral?

That should do the job, yes?


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## lilhasselhoffer (Apr 24, 2012)

Uncorruptable said:


> Hi Everybody,
> 
> Just picking this thread back up briefly, if i want to power a device that is max 3.9v, based on all of the above, can i utilise the orange 3.3v from a power supply & hook the orange to live & black to neutral?
> 
> That should do the job, yes?



Yes and no.

Yes, 3.3 is generally between 3.2 and 3.4 volts on a good power supply.  If you connect +3.3V to the positive and black to the negative you should be able to use the voltage to run what you want.  Just make sure you don't connect 3.3V negative, or any other voltage to the opposite side.

No, you will need a switch or resistor to actually get the power.  On an ATX power supply there is a lead that tells the PSU to power up.  This wire is on the 20 or 24 pin main connector, and should be the only green one if the PSU is certified to meet ATX specifications.  Connect this green wire to any black wire with either a small resistor (constant power when connected to the mains) or a switch (on-off, but plugged into mains constantly).  The power supply should no turn on and provide power to the 3.3V bus.


Finally, I have a suggestion.  Pry off the final SATA/Molex (SATA is easier) connector on one of the leads from the PSU.  The yellow wire is +3.3V, and the black is ground.  You've got everything you need, with a minimum of invasion into the power supply itself.



Edit:
To those who want to argue, the Molex connector Specification (http://en.wikipedia.org/wiki/Molex_connector) requires that black is a *GROUND*.  This SPECIFICATION supersedes whatever terminology you would like to say is the only correct answer.  Please remember that sometimes people do their research before saying anything.


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## Jetster (Apr 24, 2012)

Who says Earth. In a PC PSU black is ground

Neutral = In a single phase system the neutral wire is the return path of the circuit and may be near ground potential, in multiphase systems it carries the unbalanced current. Your friend need more training unless hes talking about the AC side of the PSU. Really its just nomenclature. No big deal


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## TheMailMan78 (Apr 24, 2012)

Arctucas said:


> For an ATX PSU, I believe the proper term for the black conductors is COMMON.



Thank you.


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## Jetster (Apr 24, 2012)

I think with a lot of us being from different parts of the world the terminology will vary


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## Uncorruptable (Apr 24, 2012)

Jetster said:


> I think with a lot of us being from different parts of the world the terminology will vary



yep, with me being located in Ireland, the Earth (Ground) would be also coloured usually green & yellow striped.

Thanks for the info above, i will go for the Yellow & Black from 1 molex connector for my power supply.

On the bridging of the green wire to a Ground/Earth to get the power to flow, what resistor would you guys recommend?


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## Completely Bonkers (Apr 24, 2012)

*Stop*

... with this guessing nonsense. I don't have time to give a full answer now, but GROUND does not equal NEUTRAL. And NEVER wire them as such. And DONT GUESS if you arent sure. If you are "playing" with the DC side of a PSU the worst you can do is fry some PC components. But if you misinform people, then they may use this misinformation on a later occasion and put themselves or other people at risk.

I'm come back later with more info - for the sake of cleaning up this thread - when I get home and have time.


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## Uncorruptable (Apr 24, 2012)

Completely Bonkers said:


> *Stop*
> 
> ... with this guessing nonsense. I don't have time to give a full answer now, but GROUND does not equal NEUTRAL. And NEVER wire them as such. And DONT GUESS if you arent sure. If you are "playing" with the DC side of a PSU the worst you can do is fry some PC components. But if you misinform people, then they may use this misinformation on a later occasion and put themselves or other people at risk.
> 
> I'm come back later with more info - for the sake of cleaning up this thread - when I get home and have time.



Without cleaning the entire thread now, can you tell me where to obtain a neutral wire in a PSU for my device please? 

Most likley i will be snoozing when you are cleaning up the thread me being in Ireland so if you can throw me the info now i would very much appreciate it.


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## TheMailMan78 (Apr 24, 2012)

Jetster said:


> I think with a lot of us being from different parts of the world the terminology will vary



This.



Uncorruptable said:


> Without cleaning the entire thread now, can you tell me where to obtain a neutral wire in a PSU for my device please?
> 
> Most likley i will be snoozing when you are cleaning up the thread me being in Ireland so if you can throw me the info now i would very much appreciate it.



Look for a wiring schematic friend.


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## brandonwh64 (Apr 24, 2012)

From my electronics engineering degree, We mainly called the black wires ground even when we created a AC to DC converter with a full rectifier as shown below 












Common and Neutral Mainly go with Alternating Current



> Neutral
> The wires of a circuit connected ultimately to the earth to receive flow "back" from a light or appliance. They are always supposed to be white. Contact with them should not normally shock you because they are normally connected to ground much better than you can be.
> 
> Common
> ...




SOURCE


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## Uncorruptable (Apr 24, 2012)

TheMailMan78 said:


> Look for a wiring schematic friend.



I had looked for some info online but wasnt really getting anywhere, i thought in the end it would be easier to register here & ask advice from people who use such devices regularly & are more knowlegable than myself.

If anyone can advise where to get a neutral in a PSU or if the balck ground is OK to use please do.

Thanks in advance.


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## TheMailMan78 (Apr 24, 2012)

Uncorruptable said:


> I had looked for some info online but wasnt really getting anywhere, i thought in the end it would be easier to register here & ask advice from people who use such devices regularly & are more knowlegable than myself.
> 
> If anyone can advise where to get a neutral in a PSU or if the balck ground is OK to use please do.
> 
> Thanks in advance.


Contact crmaris. If anyone can give you a straight answer it will be him. Hes the local PSU guru. His word is gold.

http://www.techpowerup.com/forums/member.php?u=93379


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## Uncorruptable (Apr 24, 2012)

TheMailMan78 said:


> Contact crmaris. If anyone can give you a straight answer it will be him. Hes the local PSU guru. His word is gold.
> 
> http://www.techpowerup.com/forums/member.php?u=93379



Just PM'd him there, thanks for the pointer & with him being in greece i may get a reply soon before i hit the hay, thanks again & i will report back if i am successful & the way it was done.


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## TheMailMan78 (Apr 24, 2012)

Uncorruptable said:


> Just PM'd him there, thanks for the pointer & with him being in greece i may get a reply soon before i hit the hay, thanks again & i will report back if i am successful & the way it was done.



He reviews our PSU's. His Kung Fu is strong with that one.


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## lilhasselhoffer (Apr 24, 2012)

You want to, functionally, make a bench power supply out of an ATX power supply.

The exact same project has been dozens of times.  One example can be found here:
http://tgbuilds.wordpress.com/2010/07/26/power-supply-design/


To get 3.3 volts, do what I said a few posts ago.  Green wire in 20 or 24 pin connector needs to be bridged to any of the black wires in that connector (provides on signal to PSU).  The 3.3 volt lead (yellow one if you've got a standard molex connector lead) will become hot, and to complete the circuit use the ground (ground because this is a DC source, not an AC source); in a molex connector the ground is black.


BE CAREFUL!  You're activating the power supply without a load, which isn't good for it.  Either provide a small load (a fan works well), or make sure that you don't leave the PSU on once the device you are powering is no longer in use (why I suggest connecting that green wire to a black with a switch.


AC: Green is the Earth.  Everything else is hot, because the circuit must be cyclical to have an AC voltage.  The Earth acts only as protection, and not as a functional part of the circuit.  White is generally neutral, but given the right circumstances will carry voltage.

DC: Black is ground.  Any other color carries voltage, but can be either positive or negative.  This is in reference to how the potential is oriented (High->ground is positive, Ground->low is negative).  There doesn't need to be a black (+3.3V to ground has effective 3.3V, +3.3V to -3.3V has effective 6.6V), but it is common to use the black in power supplies.  Think about not needing a ground in a flash light because the potential difference between the battery terminals is what provides electrical power.


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## Arctucas (Apr 24, 2012)

@lilhasselhoffer,

Actually, the yellow conductor is +12V, nominal.

The orange conductor is +3.3V, nominal.

You might want to correct that before someone overvolts something...

Anyway, the black conductors are COMMON, as in all tied together.

They (should) present zero volts potential with respect to earth ground, and therefore are the reference for the other potentials.

If an ATX power supply was actually DC, rather than rectified and filtered AC, one might think of the black conductors as the negative (-) terminal of a battery.


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