Is earth/ground important?

MassMan · Post by **MassMan** » Thu Feb 03, 2005 11:24 am

I've read the psu guide and searched the forums but haven't been able to figure out whether earth (ground for you yanks) is that important?

btw considered placing the question in the newbie forum, but then I thought the psu freaks would probably be the best to ask. Feel free to move the post if it is better suited for the newbie forum.

SometimesWarrior · Post by **SometimesWarrior** » Thu Feb 03, 2005 11:41 am

The Xbit-labs PSU Testing Methodology article talks a bit about when a ground is important for a PC, and when it isn't. Check page 4, maybe it will answer your question?

Jan Kivar · Post by **Jan Kivar** » Fri Feb 04, 2005 2:40 am

It is recommended to plug the computer to a grounded outlet. If you do plug the computer to a non-grounded outlet, don't do any "hot-plugging": shut down all devices before making new connections.

The problem derives from different ground potentials. If the computer is ungrounded, the entire computer will float in half of the AC voltage from the outlet (115V/60V). Now, if you connect the computer to an amplifier, which is connected to a TV, which is connected to an aerial (or cable), you might get some problems, since the aerial network is probably grounded somewhere else and thus has a different potential.

In these cases You might actually get a small jolt on your fingers if you hot-plug (and even if you don't, since the PSU is on whenever the PSU is plugged in).

Cheers,

Jan

ChristianN · Post by **ChristianN** » Sun Feb 06, 2005 5:22 am

In my experience, you can get away without ground if you run all devices from the same powerstrip / wall outlet.

This is, as Jan Kivar allready said, mostly an issue when hot-plugging stuff. It's fully possible to actually destroy stuff with different ground potential, my most expensive victim as of yet was a $1000 Harman Kardon amplifier a few years back

Luckily, I had good insurance back then and got most of it covered.

Anyway, when you connect different equipment with different ground potentital you _really_ should disconnect it first. You should also be careful not to touch open metal on devices with different ground potentials, especially one floating (115/60 v) and one properly grounded.

Between my freezer and a server I have a 190vac ground difference. Suffice to say; touching both of these at the same time hurts like bloody hell.

peteamer · Post by **peteamer** » Sun Feb 06, 2005 6:46 am

The earth/ground is there for SAFETY reasons !!!!!!!!!!

If you are getting Potential Differencies between grounds, you have seriously flawed wiring/mains leads/equipment in your home.
(Differencies may be measurable... but should be negligable.)

190VAC is potentialy lethal.

It's part/mainly why America uses 110V... and why professional building companies in the U.K. are required by law to use 110VAC 'centre earthed' transformers/equipment. (Effectively never more than 55V)

Jan Kivar wrote:The problem derives from different ground potentials. If the computer is ungrounded, the entire computer will float in half of the AC voltage from the outlet (115V/60V).

I'm not sure that's correct... I would only expect that if the computer PSU wasn't functioning correctly... or am I thinking wrongly?...

Come on Boys... even my my 'significant other' knew why the earth was there when I asked if she knew.....

Pete

Doomer · Post by **Doomer** » Sun Feb 06, 2005 1:10 pm

peteamer wrote:
Jan Kivar wrote:The problem derives from different ground potentials. If the computer is ungrounded, the entire computer will float in half of the AC voltage from the outlet (115V/60V).
I'm not sure that's correct... I would only expect that if the computer PSU wasn't functioning correctly... or am I thinking wrongly?...
Pete

There is indeedy half of the AC voltage at the case if the PSU is connected to ungrounded outlet. It sounds dangerous but because the actual current is very small(something like 0.5mA) it can only kill your hardware.

But don't touch that ungrounded case and a grounded object(a radiator for example) at the same time. And DO NOT try to ground your computer to the radiator!

Jan Kivar · Post by **Jan Kivar** » Mon Feb 07, 2005 9:18 am

peteamer wrote:
Jan Kivar wrote:The problem derives from different ground potentials. If the computer is ungrounded, the entire computer will float in half of the AC voltage from the outlet (115V/60V).
I'm not sure that's correct... I would only expect that if the computer PSU wasn't functioning correctly... or am I thinking wrongly?...

See this schematic of a 200W ATX PSU made by DTK. See that the SHIELD is connected to the junction of C5 and C6. So, normally this illicit current is going to the ground, but if if is unconnected in the outlet, it'll make the PSU/case to float at half of the AC voltage. (Actually I think it would be illegal to have a grounded outlet with no electrical connection made to the ground pin.)

As Doomer mentioned, the leakage current is small, so it'll basically just hurt if you get zapped, despite the high voltage. Current kills, not voltage.

In most of Europe nearly all other devices use the flat C-type connector (aka Europlug, see pictures here): TVs, VCRs, etc. On the site it's said that if the device needs less than 2.5A, it can use the Europlug. One can also get a similar jolt if one touches the antenna plug in the TV and the cable plug at the same time (when the TV is plugged to the wall socket). It is though a bit different setup with these devices, as the covers are plastic/metal covers not connected to the ground (obviously).

peteamer wrote:It's part/mainly why America uses 110V... and why professional building companies in the U.K. are required by law to use 110VAC 'centre earthed' transformers/equipment. (Effectively never more than 55V)

Yeah, same here in Finland, but there is no requirement to upgrade the existing wiring jobs. So, live in an old house, and most likely you'd have grounded outlets in kitchens only, or not even there if it's really old house.

It is also illegal to use an extension cord to extend the grounded outlet to another room. And as Doomer said, do not connect the ground to the radiator. It might kill your neighbour (if you live in a terraced house/apartment) in case of a electrical failure.

Now, I'm not a licensed electrician, so if there is any false information, please do correct it.

Cheers,

Jan

Elixer · Post by **Elixer** » Mon Feb 07, 2005 10:33 am

Jan Kivar wrote:(Actually I think it would be illegal to have a grounded outlet with no electrical connection made to the ground pin.)

Illegal or not, my house has a lot of these. I'd say that about 2/3 of the 3 prong outlets in my house have the ground plug, but are not grounded. I solved the problem in one room by running a wire outside through a window to a 4 foot steak in the ground. After that my power tester no longer read any problem. I have ran computers for years on ungrounded power without any problem though. From what I understand not having a ground increases your computer's vulnerability to power strikes, particularly lightning, because the static discharge of lightning is trying to reach ground, and electricity takes the past of least resistance so having a ground lets the discharge more easily go to the ground instead of your computer.