Electric case

[Pelle]

Hi!

I bought a new computer some weeks ago. It was "built" from its components in the shop by pros, the only modification I've done is to insert a second hard-drive (as primary slave). Everything works excellent, but I'm concerned because the case is sometimes electric. Sometimes when I touch the case I can feel a very notable current flow through my body. Sometimes I feel the current only when I touch the case and a radiator at the same time. And sometimes I don't feel it at all. What could be the cause of this and is my beloved one (the computer) in danger? The case is a "Black Thunder Miditower Black/Silver 300W ATX" and it is standing directly on a wooden floor.

 

[etp777]

Don't mess with it, take it immediately back to place you got it from and tell them to fix their screwed up system. Shouldn't feel a noticable current when you touch your case.

 

[Tavelkyosoba]

well that makes sense, but what would cause something like that, i'd like to know if it ever happened to me(unlikely as most of my cases are being replaced by homemade wooden ones)


I've got a book of matches,
I've got a can of kerosene,
I've got some bright ideas involving you and me.

 

[Crashman]

The power supply connects to a 3-pin power cord, the third pin is for grounding the case, it's possible you've used an adapter to connect the cord to a 2-pin wall socket, or that the person who installed the power in your building didn't ground the third connector properly! Try it in another building!

<font color=blue>Only a place as big as the internet could be home to a hero as big as Crashman!</font color=blue>
<font color=red>Only a place as big as the internet could be home to an ego as large as Crashman's!</font color=red>

 

[Crashman]

LOL, d00d, it doesn't matter HOW crappy or defective a system is, power supplies ALWAYS have the housing grounded to the third wire of the cord, the only way you could have such an issue is if your plug isn't grounded, which would make it a building or user problem.

<font color=blue>Only a place as big as the internet could be home to a hero as big as Crashman!</font color=blue>
<font color=red>Only a place as big as the internet could be home to an ego as large as Crashman's!</font color=red>

 

[etp777]

I stand corrected. Thought didn't even cross my mind, do my own wiring, and one of first things I ensure in a new house is that I've got a good ground(habits from when I use dto do radio stuff).

 

[Crashman]

Yes, a housing litterally cannot be charged as long as the ground prong is going to earth ground. Typical reasons it doesn't are: Ungrounded 3-prong to 2-prong adapters, 3rd prong of socket ungrounded, lack of an earth ground in the building.

<font color=blue>Only a place as big as the internet could be home to a hero as big as Crashman!</font color=blue>
<font color=red>Only a place as big as the internet could be home to an ego as large as Crashman's!</font color=red>

 

[Pelle]

3-pinned power cords? I've never seen such a thing! Here in Sweden, grounded power cords don't have a third pin but instead splints on the side of the cord which get contact with splints on the side of the grounded socket. This way a grounded cord can be inserted into an ungrounded socket directly.

Anyway, we don't have grounded sockets in this villa, except in the kitchen. But we have had several computers running here for ten years without any problems, so is this really an important thing to fix? I suspect it will be expensive to have all power cables ripped out of the walls and exchanged, if that is what's needed.

 

[upec]

In Taiwan we only have 2-prong too. The ground is biuld into one of the 2-prong. It should be fine for most eletronic equipments.

 

[Crashman]

The international standard for ALL AT/ATX power supplies is 3-pin. Pull the cord out of your computer an look at it! The OTHER end of the cord...the one that plugs into your wall, is the "problem". You could of course find an alternate way to ground the case. Also, try the thing in your kitchen and see if the problem goes away!

<font color=blue>Only a place as big as the internet could be home to a hero as big as Crashman!</font color=blue>
<font color=red>Only a place as big as the internet could be home to an ego as large as Crashman's!</font color=red>

 

[Tavelkyosoba]

isn't the third pin really just a safty ground? from what i've learned it doesn't do anything until there's a short, then it safly grounds the hot wire...or something like that, i can't remember exactly.

so do those 3 prong to 2 prong adapters connect the safty ground to the normal ground??

i've learned so much from you crashman, its incredible.

I've got a book of matches,
I've got a can of kerosene,
I've got some bright ideas involving you and me.

 

[Crashman]

Most high-power items with metal casings (such as the steel shell on power supplies and the aluminum shell on some heavy duty power tools) have a separate ground circuit for the power board and a separate one for the housing. U.S. style 3-pin to 2-pin adapters have a ground loop that's SUPPOSED to be screwed down by the cover plate screw and ground to the power outlet housing through that screw. Most people use them without grounding them.

<font color=blue>Only a place as big as the internet could be home to a hero as big as Crashman!</font color=blue>
<font color=red>Only a place as big as the internet could be home to an ego as large as Crashman's!</font color=red>

 

[Tavelkyosoba]

ohhh so thats what that little loopy thing is! next time im at my girlfriends house ill properly ground her computer to the wall outlet.

I've got a book of matches,
I've got a can of kerosene,
I've got some bright ideas involving you and me.

 

[Crashman]

LOL, yes, that loop is there for a reason!

<font color=blue>Only a place as big as the internet could be home to a hero as big as Crashman!</font color=blue>
<font color=red>Only a place as big as the internet could be home to an ego as large as Crashman's!</font color=red>

 

[jamarno]

Most power supplies have low-value capacitors connected between each line and ground to help block RF, so if an ungrounded outlet is used, the case of the supply will reach half the line voltage. Because each of these capacitors is only about 5nF, the amount of current will be limited to less than 1mA.