Electrifying sensation whilst soldering with ESD wrist strap

[king.oslo]

Hello my friends,

Lately I have been feeling current flowing through my body whilst soldering using my ESD strap. The experience is not shocking, but it is enough to make me stop soldering, to take the strap off.

I probed my board, solder and iron relative to ground potential, but I could not find AC or DC above 4V anywhere using a averaging handheld DMM, true RMS 6.5digit DMM or oscilloscope. Except when I measured the soldering iron with the true RMS meter. It saw 55VAC relative to ground. But when I went to probe it with the oscilloscope, I found nothing. Could my DMM be lying? Or is it likely that it went low before I came to probe it with my scope? Now I am not sure where else to look for the source.

I want to find and eliminate the source. It worries me a bit to think there may be a hazard somewhere on my bench.

What are your thoughts?

Kind regards,
Marius

[alm]

What is the resistance between the ESD strap and ground? This should be at least 1 Mohm, so currents should not create any sensation. I would check the grounding of your mains sockets, wrist strap and soldering iron. If there is current flowing through the wrist strap, there must be a relatively large potential across it compared to the resistance. 4 V across 1 Mohm does not create a tingling sensation. I would fix both the potential and the wrist strap resistance.

[king.oslo]

Wrist strap resistance is 1M. I will go sit in the electric chair and tell you the potential across it whilst soldering. Please just give me a minute. I am not looking forward to it Electrical appliances where i live, unfortunatly does not have ground in this building. I am using a cold water pipe for ESD GND.M

[Psi]

If your wrist strap has 1Meg to ground then it isn't part of the circuit responsible for the sensation.
Unless you have leakage from the 11kV mains line somehow, but that is extremely unlikely.

[king.oslo]

alm, Psi, I went back to the electric chair to solder like normal. Now I get no tingling sensation. Damn.

Psi, could you be wrong? Once I took the wrist strap off, I felt nothing, when I put it back on, the sensation was back. I did this just to be sure it was the strap. I understand that 1M + resistance of skin = high resistance, but there is no doubt that current was flowing, and disappeared once I took the strap off.

Kind regards,
Marius

[Ajahn Lambda]

Strange question, but are you wearing good shoes?  And are you working on a concrete floor?


Don't laugh, I've got an old non-isolated amplifier that will give you a nasty tingle when you're touching the strings of an attached electric guitar, given those situations.  My feet became the ground connection, on a concrete floor with a small amount of moisture (it was a basement).

[T4P]

Does your iron have a earth pin ? you'd better have one on your iron .

[king.oslo]

Does your iron have a earth pin ? you'd better have one on your iron .

At the minute, it doesn't.

Strange question, but are you wearing good shoes?  And are you working on a concrete floor?

I am sitting on a rubber mat with wool socks.M

[SoftwareSamurai]

If your wrist strap-to-ground has a solid 1M of resistance, you're probably not feeling a DC current. But it is possible that you're feeling an induced AC flow. If your soldering iron isn't properly grounded, it could, with just the right conditions, cause an AC feedback loop to form between it, you, and the surrounding environment. Sitting on a rubber mat with wool socks insulates you from earth ground extremely well, so your wrist strap is the only ground potential for the AC to couple to, hence why you feel it only when you have it on. If this is the case, hunting down the source is going to be like chasing a ghost, since doing such seemingly non-important things like moving your chair over an inch might disturb the feedback loop just enough to break it.

Having said that, I would take a closer look at your soldering station and the power supply to make absolutely sure there isn't an intermittent short somewhere, just to be safe. And make sure it's properly grounded. Most of the time these mysterious tingles are due to equipment that has a floating ground while powered by AC.

[ejeffrey]

Does your iron have a earth pin ? you'd better have one on your iron .

At the minute, it doesn't.

You mean it is designed to be earthed but you have defeated that somehow?  Try fixing that...

[G7PSK]

You say that the earth is via a water pipe, has any repairs to the water supply taken place, like a new piece of plastic pipe inserted, also if your soldering iron is meant to be earthed and is not due to no or poor earth on the system that could well be your problem you say that there is 55 volts on the earth side of your iron relative to to your earth on the wrist strap this will give you a tingle even with the 1M ohm in the strap if as is quite likely the metal contact of the wrist strap is placed over a nerve, The other thing is it might not be electrical problem I used to get tingles in the wrists when working, it was the first sign of carpal tunnel syndrome, it started low and slow and increased until i had to go and see a doctor, ended up having surgery to fix the problem.

[king.oslo]

Does your iron have a earth pin ? you'd better have one on your iron .

At the minute, it doesn't.

You mean it is designed to be earthed but you have defeated that somehow?  Try fixing that...

Sorry, I can see that what I wrote was incomplete- The soldering station has earth contacts on the socket, but the building I am in does not have a lead going off to earth.M

[alm]

If a piece of equipment has an earth contact, it is designed to be used with an earthed socket, using it without earth connection defeats its safety features. A single fault (eg. loose wire) could shock you, something that would require a double fault (much less likely) if an earth connection was in place. It's quite likely that there is some leakage current going through the mains input filter which is supposed to flow through the earth pin, but is now flowing through your body when it has a low impedance connection to earth.

A water pipe is not a solid earth connection, and earthing via the water pipe is not even allowed in many countries. As already stated, water pipes are routinely replaced with plastic pipes, and it's not very nice for the plumber to get shocked because something you 'earthed' via the water pipe has a fault.

[Monkeh]

Does your iron have a earth pin ? you'd better have one on your iron .

At the minute, it doesn't.

You mean it is designed to be earthed but you have defeated that somehow?  Try fixing that...

Sorry, I can see that what I wrote was incomplete- The soldering station has earth contacts on the socket, but the building I am in does not have a lead going off to earth.M

You should get that fixed. It can't possibly meet regulations.

[T4P]

You need a earth pin in your home mains .
If not you are just gonna blow things up with ESD by accident with your iron 
No actually the most important thing is that something doesn't accidentally short out to the metal body in your iron .

[IanB]

The soldering station has earth contacts on the socket, but the building I am in does not have a lead going off to earth.

Are you saying that all of the electrical sockets in your building look like this one?

http://electricaloutlet.org/type-c

And that none of  them look like this one?

http://electricaloutlet.org/type-f

If so that is rather unfortunate. It means you cannot safely buy or use any appliance that has an earthed Schuko type plug, including your soldering station.

[king.oslo]

IanB, that is true. I am thinking about running a wire off to earth ground.M

[mariush]

You should have at least one socket with ground in the house. Usually you find such sockets near the bathroom, as were meant for washing machines or hair driers.

You should have ground wire through the sockets - unless you house is really, really old.  Try opening the faceplate of a socket, maybe you actually have the cable there but it's not connected to anything.

If you find the grounded socket, just use long power strip... otherwise if you have central heating or something that goes into the ground eventually you could improvise a ground wire by typing the end to an exposed part of the metal pipes. But this later part is not safe.

[king.oslo]

You should have ground wire through the sockets - unless you house is really, really old.  Try opening the faceplate of a socket, maybe you actually have the cable there but it's not connected to anything.

Wow! You are right. Under the faceplates I found the good old green/yellow wire. How do I measure whether it actually goes off to mains ground? Measure the voltage between phase and ground? The fact that the faceplates was the C-type, makes me worry about this.

The house is 70 yrs old.

Kind regards,
Marius

[IanB]

Wow! You are right. Under the faceplates I found the good old green/yellow wire. How do I measure whether it actually goes off to mains ground? Measure the voltage between phase and ground? The fact that the faceplates was the C-type, makes me worry about this.

Go and have a look in the cupboard where the circuit breakers are. If you can see big green and yellow wires in there bonded to metal pipes or other objects it is likely the building has been rewired recently to modern standards, especially if you find circuit breakers and not fuses. If there is evidence of proper earthing arrangements where the circuit breakers are then the green and yellow wire behind the socket is almost certainly a proper earth. If so you could replace type C sockets with type F sockets and get proper grounding.

Is the building yours or does it belong to someone else? If there is a landlord you will have to ask the landlord to have the sockets modified.

[alm]

A neat trick I once picked up from a Fluke appnote is to measure the voltage between phase, neutral and earth. Only consider these measurements if you have the equipment, experience and confidence to measure live mains wires. Neutral and earth are generally bonded somewhere, but the current flowing through the neutral wire causes and IR drop compared to the earth wire, through which no current is flowing. You're using the earth wire as a sense connection to the earthing point. The voltage between neutral and ground plus the voltage between neutral and phase should be the same as the voltage between ground and phase. This allows you to quickly verify correct wiring. It's not a replacement for proper earth bond resistance and insulation resistance tests, but it should give you a clue whether it's connected to PE or just a loose wire (the latter would be against the code in many countries).

[king.oslo]

A neat trick I once picked up from a Fluke appnote is to measure the voltage between phase, neutral and earth. Only consider these measurements if you have the equipment, experience and confidence to measure live mains wires. Neutral and earth are generally bonded somewhere, but the current flowing through the neutral wire causes and IR drop compared to the earth wire, through which no current is flowing. You're using the earth wire as a sense connection to the earthing point. The voltage between neutral and ground plus the voltage between neutral and phase should be the same as the voltage between ground and phase. This allows you to quickly verify correct wiring. It's not a replacement for proper earth bond resistance and insulation resistance tests, but it should give you a clue whether it's connected to PE or just a loose wire (the latter would be against the code in many countries).

Lets see, you are saying, measure phase relative to earth ground and phase relative to neutral? If these measurements are equal, it indicates that I have found earth ground wire?

Go and have a look in the cupboard where the circuit breakers are. If you can see big green and yellow wires in there bonded to metal pipes or other objects it is likely the building has been rewired recently to modern standards, especially if you find circuit breakers and not fuses. If there is evidence of proper earthing arrangements where the circuit breakers are then the green and yellow wire behind the socket is almost certainly a proper earth. If so you could replace type C sockets with type F sockets and get proper grounding.

I will check this tomorrow. Thanks.M

[king.oslo]

Alm, did I understand your neat trick?

IanB, the cupboard holds old fashioned fuses. No modern circuit breakers. I could spot some green and yellow wire in there. The wires went off into some pipes to somewhere else. No idea where.

What do you guys think? Is this good earth ground?M

[G7PSK]

Most likely not, as you appear to have grounding problems. You need to find a good ground and test for resistance and potential between the good ground and the wiring ground that you have. 

[king.oslo]

Most likely not, as you appear to have grounding problems. You need to find a good ground and test for resistance and potential between the good ground and the wiring ground that you have.

Should I hammer a copper stick into the ground and measure the resistance between this and the green and yellow wires behind the faceplates?M