Jumping Earth to Ground wires on a PSU

[-Jackson]

I'm pretty sure a lot of you have seen forum posts (namely around the Watercooling section) about jumping the Earth (green) wire to a Ground (black) wire to start up a PSU via the 24-pin ATX plug.
The other day, I told this to my Hardware teacher at my college and he called me an idiot :lol:
I'm sure this has been asked plenty of times, but is it actually safe to do so? I've done it several times myself and it seems fine. I just want to prove my teacher wrong.

 

[alexoiu]

It's actually what happens when pressing the power button http://www.youtube.com/watch?v=5FWXgQSokF4

The green is PWR_ON (or PS_ON), not Earth.

 

[ittimjones]

AWESOME! Did not know this.

I'm guessing that it is very important to triple check that you indeed do have the green and a black wire bridged. lol

 

[alexoiu]

More details: http://www.tomshardware.com/reviews/power-supply-specifications-atx-reference,3061-6.html
"When the switch is pressed, the PS_ON signal is grounded. When the power supply sees the PS_ON signal drop to 0.8 V or less, the power supply (and system) is turned on"

 

[-Jackson]

I was quite shocked (no pun intended) when he told me that it was extremely dangerous to do so, I mean I'd even touched the paperclip while it was bridging the green to black wires and it seemed perfectly safe to me. Man, I'm going to get myself killed someday :lol:
Well, when I told him about it I did say "green" wire, so I don't blame him for mistaking it for an Earth, but I guess I can still prove him wrong nonetheless. ;D
Thanks Alex

 

[RetiredChief]

Max voltage on 24 Pin connector is 12V. A normal person can not even detect that low of a voltage, let along get "shocked" - LOL

 

[-Jackson]

Of course! Silly me

 

[FinneousPJ]

What the heck would be an Earth wire?

 

[alexoiu]

earth wire = ground wire

 

[FinneousPJ]

"Earth to Ground wires" would suggest they're different :lol:

 

[InvalidError]

Max voltage on 24 Pin connector is 12V. A normal person can not even detect that low of a voltage, let along get "shocked" - LOL

Back when I was a kid, lots of people in my family and neighborhood used the 'lick test' to verify whether or not a 9V battery was good or not... I remember fresh 9V batteries producing a rather sharp tingle

This isn't exactly a typical 'use' scenario but less than 12V is definitely detectable by most people in that case!

Under normal circumstances though, it takes 30-40V to start feeling something through healthy skin. Under 50V, the likelihood of a potentially lethal shock is pretty low but the surprise effect may contribute to secondary injuries such as from dropping tools, yanking something or losing balance.

 

[InvalidError]

"Earth to Ground wires" would suggest they're different :lol:

Depending on context, they can be.

Within the same device and even the same PCB, you can have "analog ground", "digital ground" and "ground" where 'analog ground' is a ground island on the PCB dedicated to service a certain set of particularly sensitive components such as analog audio inputs/outputs, 'digital ground' may be other island(s) dedicated to a set of either sensitive or particularly noisy digital components and 'ground' being the common reference for everything and usually gets tied to Earth through the ground wire/pin on AC power cables. There may also be more "local grounds" for stuff like WiFi, 3G/4G, BT, etc. either on the same PCB as everything else or simply by virtue of being on a separate card/module with its own power and ground planes.

Each island usually gets tied to the common ground using small inductors and small (sometimes even zero-ohm) resistors.

 

[RetiredChief]

^ yea, I've heard of the "Lick" test for 9 V Batteries.
More foolishly, some electricians test for 120VAC with there finger - Little secret, they use the fingernail. STILL DO NOT RECOMEND.

Also, generally Blond, blue eyes feel have a lower voltage tolerence - has something to do with skin pigmintation (lower body resistance) - If memorry serves me right.

 

[shanky887614]

Max voltage on 24 Pin connector is 12V. A normal person can not even detect that low of a voltage, let along get "shocked" - LOL

50v is safe to be shocked by


for example the lights in your bathroom at least downlighters are 50v

search selv lighting





make sure to check the pinout diagram first to makesure you are selecting the right pins if you havent done it before


better to be sure than not sure


p.s. your college tutor sounds like an idiot




most electricians check got voltage with a voltstick even someone as thick as a brush can tell if its working or not as there is a light on a lot of them that shows if batteries are dead and if there is power the tip glows

(eddie currents, basically the magnetic field given off by the flow of current. transformers work by using the same basic principle as voltsticks and electric toothbrush chargers

 

[alexoiu]

I think that the pofessor's point was that in case of a faulty power supply (where the output is not electrically isolated from the main and the protection doesn't work) a higher voltage would get through the ATX connector.
The 2 pins involved in shorting are not dangerous (ground and PWR_ON), but theoretically, other pins would be.
I don't think that one can find such damaged PSU in real life.

 

[InvalidError]

50v is safe to be shocked by

Although much less likely, 50V can still be lethal if all the 'right' circumstances line up. Getting the 50-60mA needed to cause cardiac arrest is possible at 50V if you happen to have bruised skin with serum/sweat on your chest and back and 50V across. Not likely but not impossible.

BTW, "voltsticks" work by sensing the 60Hz electrical field using capacitive coupling between the wire and tip. Eddie currents are considered parasitic losses in magnetically permeable electrically conductive material and their only desirable use is induction heating such as stove-tops and industrial. Toothbrush and most other "wireless" chargers work by inductive coupling where the charging base holding a transformer primary winding while the device(s) hold the secondary winding(s).

 

[FinneousPJ]

Depending on context, they can be.

Within the same device and even the same PCB, you can have "analog ground", "digital ground" and "ground" where 'analog ground' is a ground island on the PCB dedicated to service a certain set of particularly sensitive components such as analog audio inputs/outputs, 'digital ground' may be other island(s) dedicated to a set of either sensitive or particularly noisy digital components and 'ground' being the common reference for everything and usually gets tied to Earth through the ground wire/pin on AC power cables. There may also be more "local grounds" for stuff like WiFi, 3G/4G, BT, etc. either on the same PCB as everything else or simply by virtue of being on a separate card/module with its own power and ground planes.

Each island usually gets tied to the common ground using small inductors and small (sometimes even zero-ohm) resistors.

The context here of course in case you hadn't noticed being the PSU

 

[-Jackson]

Back when I was a kid, lots of people in my family and neighborhood used the 'lick test' to verify whether or not a 9V battery was good or not... I remember fresh 9V batteries producing a rather sharp tingle

This isn't exactly a typical 'use' scenario but less than 12V is definitely detectable by most people in that case!

Under normal circumstances though, it takes 30-40V to start feeling something through healthy skin. Under 50V, the likelihood of a potentially lethal shock is pretty low but the surprise effect may contribute to secondary injuries such as from dropping tools, yanking something or losing balance.

I found out about said "lick test" when I decided to lick a battery when I was a kid, still use it today

 

[-Jackson]

50v is safe to be shocked by


for example the lights in your bathroom at least downlighters are 50v

search selv lighting





make sure to check the pinout diagram first to makesure you are selecting the right pins if you havent done it before


better to be sure than not sure


p.s. your college tutor sounds like an idiot






most electricians check got voltage with a voltstick even someone as thick as a brush can tell if its working or not as there is a light on a lot of them that shows if batteries are dead and if there is power the tip glows

(eddie currents, basically the magnetic field given off by the flow of current. transformers work by using the same basic principle as voltsticks and electric toothbrush chargers

My college teacher assumed Earth wire since I said "green", when it was actually the PWR_ON wire.. Easy mistake I guess.

 

[-Jackson]

Best answer selected by -Jackson.