Bizarre Home Electrical Problem (Pic Heavy)

[Jacob32123]

For a few months now, I have been getting shocked when I touch anything powered by a DC power supply that is not case neutral.

The problem is so odd, I figured if I posted about it, no one would believe me, but my voltmeter shows it too.

The problem occurs when you touch the output of a DC power supply or anything that is case positive or negative. For example, touching the battery charger shown below, the frame of a car while it is charging, or the battery plugged into a UPS (makes it hard to unplug)

This isn't just a little shock though like you get from licking a 9v battery, this is a big shock, like when you touch 120 VAC (turns out it is). The severity of the shock seems to vary with the output current of the power supply, but the voltage seems to have no effect.

The odd thing is, things still work. Today, I was trying to change out the battery on my UPS, but I had to put rubber gloves on to unplug it, because I got an awful shock every time I touched one of the terminals. When voltmetered across the + and - of the SLA Battery, I get 14.3 volts.

The problem seems to go on and off. It may be that I just don't notice it (I don't use anything that would shock me), but I think I have been able to use the battery charger shown below without being shocked. I have not been able to find any sort of pattern between when I get shocked and other conditions.


Anyone have any ideas on this? I would really like to fix it.

 

[Sigurthr]

We have a similar issue here in this house. What I was told by an electrician is that when incandescent lighting circuits are tied in with electrical wall outlet circuits the incandescent lights pass on an AC signal between neutral and ground. Sometimes a LOT of current and up to full line voltage can be sitting between neutral and ground and this can cause serious hazards. In my house we have about 62V between neutral and ground.

 

[Things]

Sounds to me like your mains ground is floating. Try measuring between the ground point on your mains socket and a metal pipe or some other form of ground. If you still see anything more than a few millivolts then you should definitely get it checked out by an electrician. There are VERY strict requirements on the resistance of ground conductors.

 

[lasersbee]

Sounds to me like your mains ground is floating. Try measuring between the ground point on your mains socket and a metal pipe or some other form of ground. If you still see anything more than a few millivolts then you should definitely get it checked out by an electrician. There are VERY strict requirements on the resistance of ground conductors.

I agree with that.... There could be a floating
ground... Have it checked by a professional...


Jerry

 

[Sigurthr]

Floating ground would be even worse, no safety return path at all then. Yes, do as above and check for voltage between ground and a truly grounded metal pipe. If you get no voltage between ground and GROUND but between Neutral and ground then you have as I described in my previous post.

 

[Jacob32123]

We have a similar issue here in this house. What I was told by an electrician is that when incandescent lighting circuits are tied in with electrical wall outlet circuits the incandescent lights pass on an AC signal between neutral and ground. Sometimes a LOT of current and up to full line voltage can be sitting between neutral and ground and this can cause serious hazards. In my house we have about 62V between neutral and ground.

Very interesting. I am going to try to shut off all lights and see if it stops

Sounds to me like your mains ground is floating. Try measuring between the ground point on your mains socket and a metal pipe or some other form of ground. If you still see anything more than a few millivolts then you should definitely get it checked out by an electrician. There are VERY strict requirements on the resistance of ground conductors.

2.1 volts across hot and ground 32 volts across neutral and ground

EDIT: UP to 122 across neutral and earth. I don't know what changed

EDIT 2: I might have my pin outs backwards. 32 volts across the right pin and the bottom pin.

 

[Things]

Although, I will also throw in here, sometimes cheap switchmode power supplies from China are really badly isolated, and can give you a shock from their DC output. I had a eeepc power adapter I bought off eBay cheaply that was horrible like this, every time you were touching ground and touched the computer or plug, you'd get a massive shock!

Sure enough, after a few times I got annoyed with it and destroyed it.

IF this problem happens to you on only a few devices, and all of those devices happen to be switchmode power supplies, than you could try possibly grounding their cases and - outputs to prevent them from floating.

 

[Sigurthr]

2.1 volts across hot and ground 32 volts across cold and ground

EDIT: UP to 122 across cold and earth. I don't know what changed

Hmm, 2.1V between Hot and Ground looks like a floating ground for sure. It could be as little as an improperly installed recepticle.

Here is the normal and proper conditions for a household circuit:

Between HOT and Ground - ~120V
Between HOT and NEUTRAL - ~120V
Between NEUTRAL and Ground - ~0V
Between Ground and GROUND (pipe/rod) - ~0V

 

[Things]

Yes, such little voltage between hot and ground is definitely an issue.

 

[Jacob32123]

Floating ground would be even worse, no safety return path at all then. Yes, do as above and check for voltage between ground and a truly grounded metal pipe. If you get no voltage between ground and GROUND but between Neutral and ground then you have as I described in my previous post.

No voltage between ground and a metal pipe, but 39 ohms between the two.

EDIT: see bottom of post 6

 

[Sigurthr]

Ah, well as I said if Hot to Ground is 120 and Ground to GROUND is ~0 there is no floating ground. 39Ohms isn't bad for a couple hundred feet of wiring.

You might just have the same situation I do with a "hot" neutral.

 

[n2stuff]

Sounds like a bad neutral or bad ground at the main service. Do you have overhead or under ground power coming in to your house? Also how old in your home?

 

[Jacob32123]

Sounds like a bad neutral or bad ground at the main service. Do you have overhead or under ground power coming in to your house? Also how old in your home?

Underground, 11ish years old.

 

[n2stuff]

Underground, 11ish years old.

Ok. So that eliminates critters chewing on the overhead drop. Although gofers sometimes do get the underground mains. Check the main water pipe ground around the union in the front or back of the home. Have you tested more than just your work bench area for same problem? It could just be your power supply that you are using to run your charger.

Scott

 

[Jacob32123]

Ok. So that eliminates critters chewing on the overhead drop. Although gofers sometimes do get the underground mains. Check the main water pipe ground around the union in the front or back of the home. Have you tested more than just your work bench area for same problem? It could just be your power supply that you are using to run your charger.

Scott

The charger gives me a minor shock upstairs, but I am on carpet not cement there. I think if I were on the same concrete floor upstairs, I would get the same shock. I get the same shock from the battery for the UPS, and touching the frame of any car in my garage while it is charging. Really anything hooked up to a DC power supply.

 

[MarioMaster]

Sounds like you should have an electrician check the ground rod and neutral connections for your house. I've seen a shower house at a summer camp have around 20vac on the plumbing after a control transformer in the water heater rusted badly - resulting in mild shocks when people went to use the showers. Your case however is far more severe and should be investigated immediately.

I have never heard the theory on incandescent bulbs causing floating grounds. This makes no sense to me and I'd like to hear their reasoning on how this happens.


Switchmode power supplies tend to have small capacitors that couple outputs to ground and the housing to reduce high frequency noise. With a proper ground this is not an issue, but for you - you end up with nearly full line potential on the housing.