Please help: Video cable shield + computer case = electrocution.

I am trying to build a computer. It's on desk #1 plugged into power strip which shares wall socket #1 with little reliable refrigerator that is at least 35 years old. On desk #2 is a dozen things plugged into power strip into a wall socket #2. The monitor is using this wall socket, also with a different computer at desk #2.

Having trouble with the machine I try to re-seat pci cards. Then ZAP! 120v is a really distinctive feeling!
If the DVI cable / shield is in one hand, and then touch the CASE of this computer with other hand I get ZAPPED.

I put multi-meter continuity between the two ground wires from wall socket #1 & wall socket #2, and the BEEPER is oscillating. I check continuety ground on two different spots in power strip for wall socket #2 and hear a clean beep. I check continuety ground on two different spots in power strip for wall socket # 1 and hear the oscillating beep again.

I really do not know much about A/C wiring in old house with CLOTH wrapped around the cables in the walls. Can someone tell me what is wrong here - could the refrigerator be sending voltage back into the ground ? What troubleshooting steps do I do to start correcting this?

You shouldn't be able to get a shock from the frame of the computer. That is absolutely not proper behavior.

Check the outlet with an outlet tester (available online or at any hardware store) to rule out bad wiring (if that fails, contact a licensed electrician or bring it to the attention of your land lord and begin the process of getting the wiring fixed).

If the outlet passes, I would suspect the power supply on the computer.

You have to be more specific with what you have. Do you have actual grounded outlets (3 prong), or did someone just put unconnected grounded outlets in? Is there anything plugged in that has a 3 prong plug? Are these separate circuits, or on the same circuit?

Both wall sockets have the ground. 3 holes. No rubber ground eliminator. They are older than me I do not know who wired it. The house has cloth wrapped wire.

I do not know if they are separate circuits. That is a good question I will check on - thank you.

You can use a multimeter set to read ac mains voltage and check for correct polarity and also ground/neutral faults.

Looking at the outlet, the left is neutral, the right is hot, and of course the third is ground. If you connect a lead to the right (hot), you should read 120VAC to both the neutral and ground holes. Measuring from neutral to ground should read 0VAC. Doing the same using the hot from one outlet to the ground/neutral of the other outlet should read the same values. Measuring from hot to hot may yield 240VAC or 0VAC. Neither is actually wrong, nor does it determine a whole lot other than which phase the circuit is on.

Looking at the outlet, the left is neutral, the right is hot, and of course the third is ground. If you connect a lead to the right (hot), you should read 120VAC to both the neutral and ground holes.

That's ambiguous as there is no "correct" orientation (ground pin up or down) as provided in the NEC or NFPA.

Of the two slots, the small slot is the black/hot/live wire, the wider slot is the neutral, the white wire. Modern US outlets use brass colored screws for the live connection, tinned/silver color for the neutral. The ground is the green screw...

Just because you "see" a wire on the ground pin of the outlet does not mean it is connected to anything at the other end. One of our old houses had that problem. Old wiring was two #14 wires, new wiring was #12 with ground, but there was no place to connect a ground.

Furthermore, the new wiring may be connected to the opposite hot side on the breaker box. Also a NO NO. Was not done by a licensed electrician. One room can only have power from one side of the breaker box.

We also had a house where the color codes for hot and common were reversed for some wiring.

Our house in Washington state had the TWO bare ground wires going from the breaker box, across the ceiling, to the steel cold water pipe. But hidden in the ceiling, one of the bare wires ended, only one made the full distance. Then at the pipe, there were two wires, again.

Glad you were not damaged!

Paul

avr_fred:
That's ambiguous as there is no "correct" orientation (ground pin up or down) as provided in the NEC or NFPA.

That is true.

One can install a GFCI in the circuit to protect all following outlets, but it's best to leave that to someone that knows what's going on. Too many older houses used common grounds and other oddities that would need addressed.

Still, the OP has an issue going on, and in retrospect would be best to get an electrician in there to sort it out. There's too much at stake for trial and error. Getting zapped sucks. Having an electrical fire in an old house sucks. Both can kill.

Get an Electrician in to do an inspection and test report. They will test for CPC continuity and Insulation

Better get a qualified electrician to your home quick smart to avoid some serious accident.

First, Go down to the hardware store and get an outlet tester. This is a small plug-in device that has LEDs on it. It will tell you whether the polarity / continuity is good on each circuit. They are very cheap, and very useful. Follow directions for your tester. Test every outlet in your house. This will tell you what is going on. Also test any power strip that you may be using.

The reason you're probably getting zapped is because the ground is missing on one of the outlets. Some computers use a charge pump to bump up the voltage to is much as 180V. The ground is used to do this. Do not use your computer without a proper ground/neutral connection.

If your home uses the old cloth covered electrical wiring, Your home was probably built pre-1980. It is probably time that it is updated anyway. As others have said, get a "licensed electrician" to fix any problems. Doing it yourself could be fatal, if you do not know what you're doing. Your safety, and more importantly your family safety may be at Risk.

If your home uses the old cloth covered electrical wiring, Your home was probably built pre-1980

Yes, it certainly was. Closer to 1950 is more like it for cloth insulated wire. Paper/foil wrapped jacket over pvc insulated wire (romex) was the standard in the post-WW2 US building boom.

I thought the romex was out before the grounds were in. I don't see any fabric but plenty of eyes without mouths. PS: Don't trust all GFCIs. I threw ground and hot into salt water and they just fizzed. No pop. Come to think of it, what good is a switch for testing a smoke detector?

Don't trust all GFCIs. I threw ground and hot into salt water and they just fizzed. No pop.

If your goal is to test a device, you first need to understand how it functions... otherwise, you're just testing your ignorance, not the device.