Power Strip Causing Ground Loop?

First, let me tell you that I'm a retard when it comes to electronic stuff. Anyway...

I was fiddling around behind my computer and got a nice shock. I'm trying to figure out this problem and am hoping you folks could help me out.

I get the shock when I touch any part of the back of my computer or wires, and also touch the metal part of the cable that comes in and connects to my cable modem. Here's the deal:

I live in an older house that is not grounded. The ground prong on the outlets isn't connected to ground or anything else. Also, I've determined that the coax cable coming in to my cable modem is grounded. Somthing seems to be making the ground prong on my outlet hot. I've narrowed down the problem to my power strip. I've unplugged everything from my outlet and I check the outlet for voltage. Neutral to hot gives me 110V. Neutral to ground give me nothing (actually, for some odd reason, there does seem to be a slight voltage (less than 2V). Hot to ground also gives me nothing. As one would expect.

Now, if I plug in a power strip and do the same check on one of the outlets on the power strip, I get: neutral to hot 110V, neutral to ground around 60V and hot to ground around 60V. Is this right? I've checked this with two power strips and I get the same results. What would cause this? Is the polarity on my outlet wrong? Or, am I just a dummy and am misintepreting what is going on. This misterious 60V is what give me the shock.

Howard

Todd H. ( snipped-for-privacy@toddh.net) wrote: : ...your outlet is heinously miswired.

Not miswired, just wired 40+ years ago with no ground. Couldn't I just ground the outlet myself? Run a wire from the ground in the outlet to a water pipe outside? Would that solve my problems?

Howard

There are electrical codes with which you should comply.

Howard, First, I think you should replace that outlet strip. They have MOV's between the hot and ground and neutral and ground. When an MOV gets a big surge, they start leaking current that they would have blocked before the damage. Because your ground is floating, the leakage of the two sets of MOV's has made a voltage divider between hot and neutral with the ground at the midpoint. Grounding the outlet feeding your computer is a good idea, but it may trip breakers or blow fuses if the outlet strip is really hammered.

You might think about getting your house wiring brought up to modern configuration, proper grounding and GFI outlets add a lot to the electrical safety of a house. It would probably add to the resale value as well. If you are in a rental house, good luck.

Bob

Then get that fixed by a qualified professional before you burn your house down or kill one of your children.

Sorry, Rich

Use #10 AWG solid bare copper, and if you can't afford to have it done by a qualified professional, at least have it inspected by a qualified professional.

Don't murder your children.

Good Luck! Rich

The doom and gloomers sure do come out of the woodwork. There is probably nothing at all wrong with your power strips. If they have surge protective devices in them what you are reading may be normal. Some power strips have capacitors from hot to ground and neutral to ground in addition to mov's. Mov's by themselves have some capacitance and can act like a voltage divider as one poster mentioned. The fact that you measure 60 volts would indicate that both devices are acting in the same manor and dividing the voltage equally, so they are probably ok. However because of the nature of the devices it puts some voltage on your items that are tied to the ground of the power strip.

You should run a ground wire from the ground pin on the outlet back to the power service panel (breaker/fuse panel). The service panel should have a ground wire going to a ground rod already.

Running your outlet ground wire to a ground of its own would be better than nothing but the correct way to do it is to run it right to your service panel.

Regards Gary K4FMX

Yep, I completely agree. It's rather clear that no one before Gary had much of a clue as to what was really going on here.

What you are seeing is the completely normal result of having a home system with no ground, a power strip with surge protection, and a voltmeter with a high imput impedance.

You can leave things just the way they are, but the best thing would be to update the house wiring and give yourself some good grounds. In the meantime, your surge protector only gives your computer limited protection.

A proper ground is applied at the service entrance (where the AC power enters the house) and follows the wiring out to each outlet from there. An alternate ground can still protect you from electrical shock if it is well done, but it may cause other problems and may not allow your surge limiters to protect your equipment as well.

----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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Rather scary that so many know so much as to reply ... without first learning electrical basics.

The wall receptacle safety ground must have a dedicated wire connection to breaker box safety ground. Not to earth; to safety ground. And definitely not a connection to pipes.

Wire connection to pipes must be to remove electricity from that pipe. Never make a connection intended to dump electricity into pipes. A worst case scenario, a pipe connection might only electrify a wet human in a shower or bath. Wet is the worst time to touch electricity.

Connection to earth ground also does nothing useful. The important connection to earth must be from breaker box only. A receptacle safety ground must connect to breaker box so that a wiring fault does trip the circuit breaker. No way around that grounding (bonding) requirement.

The wall receptacle, power strip, or computer need not be miswired to obtain leakage voltage. Without a safety ground, then leakage currents might cause the chassis to 'feel' electrically hot. Not a danger to a dry human. However leakage can cause damage to interconnected computer components and cause other irritating problems.

Easiest solution is to have an electrician route a properly earthed wire to that receptacle. Electricians have fancy toys that make 'impossible to route' wires simple.

If a receptacle is not safety grounded, then the circuit should be GFCIed. GFCI is a minimum necessary correction.

Better power strip is typically about $3+, no n> Todd H. ( snipped-for-privacy@toddh.net) wrote:

Is this legal in USA?Here, there are people who put shucko-plugs in old fashioned three-prong receptacles, with the result, abcence of ground (the appliance works, but is not grounded).Modern computers that work in the GHz range need very good grounding, because their case becomes hot otherwise from induced high-frequency currents.

In my house:hot to neutral and hot to ground 225 volts (3:10 pm)and, of course, neutral to ground 0 volts.I have checked every inch of the installation myself, because I think that electricity is quite a good friend,but canbecome dangerous sometimes.

Notice however that neutral even having a potential of 0 volts is run by large enough currents to cause problems in bad installations (neutral bars in distribution panels and neutrals in electric ranges e.g. tend to burn to be charcoaled completely).

Bullshit. The potential at the case is power leaked in the psu, not _any_ other parts in the computer. The psu has a filter on the input, which leaks tiny currents to ground/chassis. This has nothing to do with the cpu or any other thing. It has nothing to do with induction afaik.

if you want to carry on living i sugest you get this problem rectified imediatly. if you were living in the UK the wiring would be condemed by the power company as soon as they were aware of it.

Colin.

But ... that combination can be deadly. If you don't believe me, google "guitar amp death caps."

Oh, gawd. He's invaded yet another group.

You say your outlet has no ground, but then you say you measure voltage to ground. What are you using as the return reference for the measurements? Please think about this question carefully, and what the answer implies. Do you understand that electrical charge must have a complete path in order for electrical measurements to become useful? To understand your predicament, you should be somewhat aware of how such paths are formed.

As others have mentioned, the outlet strips have internal circuitry. This internal circuitry, the MOV's (metal oxide varistors), carry minuscule currents when normal power is applied between hot and neutral. The strips are designed to carry large transients away from both the hot and neutral circuits to ground. Having an open and unreferenced ground pin gives you access to the midpoint of a balanced voltage divider between hot and neutral, so it is natural and expected for you to read the 60V on the ground pin.

Given this information, you can conclude that you have set your computer case to the midpoint of this voltage divider by plugging it in to the unreferenced (also known as "floating") pin of your power strip. Thus, when you insert yourself as a conductor between your computer case and the cable shield that is grounded to earth at the cable entrance to the house, you can expect to feel that 60V potential difference. The neutral line will be earth grounded (possibly at the entrance of the AC power into the house), and very close to the same potential as the cable shield.

There are other interesting and complex consequences to your plan to short the computer case to a water pipe. You need to hire an electrician to get this straightened out, just as you might consult a doctor about an injury or a lawyer about legal issues.

Speaking of clues: if the OP leaves things "just the way they are," he will have an ever-present and very real 60V potential between his computer case and the cable shield. That's 60Vrms at 60Hz between bare, exposed metal conductors possibly just inches apart. Dunno about you, but I wouldn't want that.

If you have a un-grounded U-Ground outlet installed in a 2 wire UN-GROUNDED box, this is a violation of most US electrical codes. You need to replace 2 prong outlets wit 2 prong outlets UNLESS there is a ground wire attached to the 1)box, 2)the green terminal on the outlet.

Many bathroom outlet and light fixture boxes were required to have a separate (bare) ground wire connected to the cold water piping. This is fine until the addition of Di-electric union or plastic piping from the water supply. If your electric service does not have a ground rod driven into the earth, have this added to the required cold water ground bond wire at the service entrance.

, _ , | \ MKA: Steve Urbach , | )erek No JUNK in my email please , ____|_/ragonsclaw snipped-for-privacy@JUNKmindspring.com , / / / Running United Devices "Cure For Cancer" Project 24/7 Have you helped?

MODERN rules. Old rules DID require COLD WATER PIPES, but *never* GAS pipes.

, _ , | \ MKA: Steve Urbach , | )erek No JUNK in my email please , ____|_/ragonsclaw snipped-for-privacy@JUNKmindspring.com , / / / Running United Devices "Cure For Cancer" Project 24/7 Have you helped?