removing grounding wire

I wanted to connect a computer power supply with a standard cable to the net (230volt), which means i’ll only have 2 cables. So i removed the grounding. The output of the power supply is 12 volts. Touching the heatsinks gives me a shock
I know that not grounding the supply is dangerous, but i do not come in contact with it nor will it run for a long time.

Questions:

1/ i measure 10 volts between my finger and the case/ the ground of the output. Does this mean that it is defect? If not, does it influence my circuit?

2/ An opamp comparator followed by a transistor follower is connected to the output of the power supply (12volt), when measuring between the output of the follower and the ground of the power supply i measure +60 volts. How is this possible? Does it harm my components? But then when i connect the transistor follower to a resistor, then the voltage drops to 2/3 volt… (supposed to be 10 volt). I do not understand what is happening here…

Thank you for your time!

Power supplies with no earth pin are usually encased in tough plastic, so there's no metal bits for people to touch.

If you're getting electric shocks etc, and if you have removed an earth (for protecting lives against short circuit to 'active' pin etc), then might be a good idea to put it back. Otherwise, could end in tears --- either for you, or for your family etc. Need to be real careful when it comes to mains power.

ALSO......... be extremely careful about some heat-sinks of some power supplies. The reason is.... the metal of some heatsinks MAY be at mains voltage. Power supply boards of some personal video recorders (PVR) etc are like that. Pretty nasty. So, if unsure...... better not touch heatsinks of power supplies. Just google something like "heatsinks at mains potential".

Touching the heatsinks gives me a shock I know that not grounding the supply is dangerous, but i do not come in contact with it nor will it run for a long time.

And it's obviously even more dangerous if you're getting a shock!!!! And, the intensity of the shock may depend on the conditions... what else you are touching and how the current flows through your body, etc. i.e., You might feel a slight shock when you touch something, but if you touch that same thing with one hand and ground with the other hand, the current-path is through your chest (and your heart). And if your body is wet/damp you'll get more current flow, etc.

When I was a "kid" my mother told me she was getting a tingle from her waffle iron. I was wearing sneakers and I didn't feel anything. I knew a little about electricity, so just to make sure I briefly reached-over and touched the water faucet at the same time... BLAM! Huge current through my chest. As you can tell it didn't kill me but we got rid of the waffle maker.

I've never seen a computer power supply that wasn't enclosed. You're probably not supposed to touch the heatsink!

Questions:

1/ i measure 10 volts between my finger and the case/ the ground of the output. Does this mean that it is defect? If not, does it influence my circuit?

If the ground is truly earth-grounded, that's normal and safe. It's just your body acting like an antenna, picking-up electro-magnetic radiation from the power lines all-around you. If you've ver touched the input of an audio amplifier and heard a buzz, that's the 50/60Hz AC picked-up by your body. 10V is not dangerous, and you can't feel 10V.* If the ground is floating, who knows...

You usually CAN feel 60V, and anything over 50V is usually considered dangerous. 60V usually won't kill you, but there may be a higher-voltage peak/spike (with your meter showing the average) and we don't know where the voltage is coming from or if there is anything limiting it, and it may get worse (higher) under some different conditions.

2/ An opamp comparator followed by a transistor follower is connected to the output of the power supply (12volt), when measuring between the output of the follower and the ground of the power supply i measure +60 volts. How is this possible? Does it harm my components? But then when i connect the transistor follower to a resistor, then the voltage drops to 2/3 volt.. (supposed to be 10 volt). I do not understand what is happening here..

You'd have to show us a schematic. Maybe you've got a different ground/reference. i.e., It's possible to have 12V between the "red" and "black" power supply terminal also have 60V between the red-output and earth ground, if the black terminal is not earth-grounded.

Did you add the comparator & transistor, or is that built-into the switching supply? A comparator has a digital (all-or-nothing) output, so I'm not sure why you'd want a comparator on a power supply output, unless it's part of a switching supply/regulator. You're comparing what-to-what?

  • You CAN feel the voltage from a 9V battery if you touch it to your tongue!

thank you for the responses! :)

I used a crappy Chinese oscilloscoop to measure the voltage between the outputs ground and the ground of the house:

|500x374 |500x374

it's highest point is +-16volts

the voltage between my hand and the outputs ground:

|500x374 https://imagizer.imageshack.us/v2/587x440q50/r/923/oiqKlG.jpg

this looks like the net's voltage, the antenna like you said i guess.

When the project is finished i'll not have to come in contact with the circuit. So i guess i have nothing to worry about as long as nothing breaks in the power supply itself?

For some weird reason is the little circuit with the opamp & transistor now working, no idea why. (it's an lm358 wich isn't meant for a comparator circuit so that's why i had to place a transistor follower against the massive voltage drop when draining current). It's weird, it's been a problem for some time now wich i couldn't find to fix..

|500x374

The comparator & the transistor have nothing to do with the power supply itself though.

First of all, I’m not sure how accurate that Chinese oscilloscope is, You should consider it to be on the low side of voltage. Also what was your probe set to, high or low voltage. If it was set to high voltage, you can double that voltage.

safety dictates that you have an earth ground connected to your device. Having said that if it is not possible to have an earth ground, Check current potential between the earth and common wire. Be careful. Make sure you do not connect to the hotwire. If the current potential is low, Connect the common earth together. Here in the United States, it is common for these two wires to be connected together at some point. Electrical potential needs to be the same.

Unless you have wet hands, you will probably not feel any electrical shock from 10 V or even 12 V for that matter. And the amount of voltage that you can take really depends on your physical size and how wet your hands are. What may not even faze you, make kill a young child. Make sure you have the unit fully enclosed so that there is no chance of anyone getting to it.

While I cannot be sure without testing your particular power supply, I suspect what you are seeing (feeling) is voltage and current from the EMI filters. To meet government requirements for radiated (radio) emissions the designers utilize a number of components. One of these are filters from the circuit to the case (which) is meant to be grounded.

So the effects of lifting the ground are:

  • Increased EMI (could affect your cell phone reception etc)
  • Dangerous potential if touching the case and being grounded.

For safety I think it is a bad idea to remove the ground. You may think you have a handle on the possible problems but believe me you don't. This is something we learn by nature repeatedly showing that we missed something. Hopefully without any catastrophic results.

you convinced me, but how should i ground it when i have only 2 cables? would a stick pressed ±30cm into the earth connected with the ground do the job?

3 core cable is very “standard” and cheap. I really don’t see why you have used 2 core cable.

You need to Earth the PS as it is not classed as a Class II appliance

MarkDerbyshire: 3 core cable is very "standard" and cheap. I really don't see why you have used 2 core cable.

You need to Earth the PS as it is not classed as a Class II appliance

i used the wire of a vacuum cleaner for the rolling mechanism..

Then change your power supply to a class II one.