115 volts on computer case...help.

[ukracer]

I have the strangest problem.
In all the years I have messed with computers I have never an electric shock.

Well I had a couple of shocks of my old case and thought ooops. Not good perhaps it's dodgy power supply or touching board etc.

Anyway I was not that concerned as I have another case and mobo to setup.
I started weeks ago and today I was making things fit under the desk.
I grabbed the new case handle and got a bèlt......so I was now getting concerned.
I pulled out the power lead and turned the supply off and blow me I got another tingle as I was wary.

So. I got the meter out and checked what was between the case and carpet and it seems to be 115 AC.
I started pulling out cables one by one and it appears that it's when the USB cable to my OKI lazer printer that I get voltage on my PC case.

If I pull the USB cable out of PC from the laser and measure the steel part to carpet I get 86 not the full 115.

I am now about to try another USB and see what results I get but I have never experienced anything like this before. I dont have a clue what could have caused it.

 

[Stupoty]

If you think the voltage is coming from the printer via USB ?

Does the printer have a 2 pin power connector ? if so try reversing it.

 

[snoozer]

Am I right in assuming from your details your getting 86v from PC case to Carpet with the PC not plugged into the mains or the printer plugged into the USB port on the PC ?

 

[mtt.tr]

Is the computer earthed? Have you checked other earthed metal objects?

 

[snoozer]

Have you tried raising the case off the carpet, Thinking maybe some static build up.

 

[jsf55]

Wild guess here, but some of our PCs came in with a 240v or 110v input, not a loose cable touching the case from the PSU ?

 

[brightspark]

test your sockets on the wall for a bad earth . if alls ok test the 10 amp lead in to the puter and make sure you have continuity of the earth from 13 amp plug to case. if your still getting shocks its static from the carpet through your body to the earthed case . had a guy getting shocks off his plastic light switch last week and he couldn't understand it the spark was jumping off him to the earthed screws on the switch just told him to put a blob of silicone over them to stop iti get zapped of the dogs nose when he touches your face and taking jumper off on a nights like blackpool iluminations

 

[ukracer]

Am I right in assuming from your details your getting 86v from PC case to Carpet with the PC not plugged into the mains or the printer plugged into the USB port on the PC ?

No...I am getting 86 volts between the outer case of the USB plug that fits into the PC... And the carpet. Whilst it's plugged in to Lazer printer.

 

[ukracer]

Is the computer earthed? Have you checked other earthed metal objects?

Well I have plugged in another USB item and checked whilst that is plugged into the PC.

I do not get any voltage between case and carpet.

If I do the same with the USB lead from the Lazer printer I get 115 volts between case and carpet.

I have tried another lead and it's the same so not a duff lead.

 

[mtt.tr]

Well I have plugged in another USB item and checked whilst that is plugged into the PC.

I do not get any voltage between case and carpet.

If I do the same with the USB lead from the Lazer printer I get 115 volts between case and carpet.

I have tried another lead and it's the same so not a duff lead.

So whats the voltage on the laser printer usb to carpet sounds like that is at fault

 

[ukracer]

Wild guess here, but some of our PCs came in with a 240v or 110v input, not a loose cable touching the case from the PSU ?

Nope... As I said (I think I said anyway. Lol)
The PC has no cables attached to it.....even the main power cable is removed.

The only time I get a reading on the meter of 115 (between case and carpet) is when the USB cable coming out of the OK I lazer is plugged into the PC. Nothing else is plugged into PC and power supply is drained.

 

[Can'tWeld]

Two things:

- the computer case should be grounded via the three pin lead. Either the socket has no ground, the 3 pin cable is faulty or the PSU does not have a ground connection from the three pin connector to the case.

- getting tingles off the printer usb lead is not necessarily a problem. Some devices with a switch mode mains adapter and no ground have a capacitor between the mains and low voltage sides of the power supply, for interference suppression purposes. The current available is very low but it will show up to several hundred volts on a digital multimeter. Mobile phone chargers sometimes do this too, I get a slight buzz off my phone when charging. Sounds dangerous but isn't.

But the key point here is that the pc case should be grounded so you should never feel a tingle or read any voltage on the pc case itself as long as the mains lead is plugged into it.

 

[ukracer]

So whats the voltage on the laser printer usb to carpet sounds like that is at fault

Yes I agree I think it's the Lazer printer.

It's highly likely that Lazer printer was plugged into the other PC when I kept getting zapped. But like Bright Spark suggested I put it down to static at the time.

I get 86 if I test any USB cable plugged into it.
It's reading 115 if I try between PC case with the USB cable actually plugged into PC.

I am fairly certain it is the Lazer causing it but wondered what sort of thing might go wrong to cause that behaviour.

 

[mtt.tr]

Its really odd because the usb and computer should be earthed so any stray voltages should go to earth.

It would be worth checking you have a functioning earth at the socket

 

[ukracer]

Two things:

- the computer case should be grounded via the three pin lead. Either the socket has no ground, the 3 pin cable is faulty or the PSU does not have a ground connection from the three pin connector to the case.

- getting tingles off the printer usb lead is not necessarily a problem. Some devices with a switch mode mains adapter and no ground have a capacitor between the mains and low voltage sides of the power supply, for interference suppression purposes. The current available is very low but it will show up to several hundred volts on a digital multimeter. Mobile phone chargers sometimes do this too, I get a slight buzz off my phone when charging. Sounds dangerous but isn't.

But the key point here is that the pc case should be grounded so you should never feel a tingle or read any voltage on the pc case itself as long as the mains lead is plugged into it.

Ah Ah. I like replies for dummies.

First thing I did was pull the mains plug from the PC....it's also likely to be the same lead used with the previous PC as it was/is coming from a 4 gang extension socket that is clipped onto the computer desk... .that in turn goes to the switched wall socket.

 

[ukracer]

Its really odd because the usb and computer should be earthed so any stray voltages should go to earth.

It would be worth checking you have a functioning earth at the socket

It's not plugged in to the mains.....but it was so yes it may not have a functioning earth...I am going to check now.

 

[Can'tWeld]

What I would do to start with, is check your socket has a decent earth connection.

But if it only does it when the computer is not plugged into the mains, there is likely no problem as long as it is a slight tingle and not a proper belt.

Does the printer have a 2 or 3 pin power cable?

 

[voipio]

I'm intrigued by the measured voltage to the carpet. What sort of carpet is it? All I get when connecting a test meter between live and the carpet is 0V, with some flicker in the last digit. Let's explain that a bit more. Meter on table, +ve lead into live pin on mains socket, -ve lead hanging above floor = 8.5VAC, -ve lead stuck into carpet = 8.5VAC i.e. the reading is down to the meter's capacitance in free space. The carpet doesn't conduct.

 

[mtt.tr]

It's not plugged in to the mains.....but it was so yes it may not have a functioning earth...I am going to check now.

You should be able to meaure 230v between live and earth. Neutral and earth should read 0v or very close Please don't do this unless you are competent.

 

[ukracer]

What I would do to start with, is check your socket has a decent earth connection.

This might sound stupid. And I do have a remote cable tester if needed but I am assuming I am having a brain @££_& as I can't see many people having one.
How do I test the socket easily.?