I was changing the rod on my arc welder and put my elbow down on the wet ground and I must have completed the circuit because my thumb got tingly. I guess I was asking for it because the ground was wet and my gloves were wet. Anyways, shouldn't the GFCI of tripped or not?
No. The GFCI looks at the power going out of the wall, to the primary coil of the welder transformer/power supply, and back into the wall - if out does not equal in, it trips. But a GFCI cannot tell what's happening on the secondary of the welder - no difference to it if you are getting zapped or steel is getting welded. You'll just have to depend on your brain.
Michael Shaffer wrote: Anyways, shouldn't the GFCI of tripped or not?
Nope.
The welder is essentially an isolation transformer. The GFCI is only looking for a ground fault on the primary side of the transformer. You got a shock from the secondary side, and a primary GFCI won't do a thing to prevent it, as you discovered....
Bob Weiss N2IXK
| Michael Shaffer wrote: | Anyways, shouldn't the GFCI of tripped or not? | | | Nope. | | The welder is essentially an isolation transformer. The GFCI is only | looking for a ground fault on the primary side of the transformer. You | got a shock from the secondary side, and a primary GFCI won't do a thing | to prevent it, as you discovered.... | | Bob Weiss N2IXK
Is it a total isolation? Or is there a ground-to-ground connection between primary and secondary?
It's total. But that is not relavent to the GFCI issue.
Tm
What everyone says is true about the secondary... It won't trip. But does the GFCI work itself? There should be a test switch and a reset button on it to simulate a ground fault.
Results?
|> | Michael Shaffer wrote: |> | Anyways, shouldn't the GFCI of tripped or not? |> | |> | |> | Nope. |> | |> | The welder is essentially an isolation transformer. The GFCI is only |> | looking for a ground fault on the primary side of the transformer. You |> | got a shock from the secondary side, and a primary GFCI won't do a thing |> | to prevent it, as you discovered.... |> | |> | Bob Weiss N2IXK |>
|> Is it a total isolation? Or is there a ground-to-ground connection | between |> primary and secondary? |>
| | It's total. But that is not relavent to the GFCI issue.
It can me. If there is a ground or neutral connection between primary and secondary, it can form an additional path, creating a common ground for the otherwise separately derived system. A ground fault can then flow from a hot wire on the secondary, to real ground, to the ground or neutral wire, to the power connection coming into the transformer, and over the ground wire between primary and secondary completing the circuit. It is then a potential shock path. If the ground clamp comes loose on the working object, you may still have a circuit if that object touches ground in some way (like through human contact).
If that connection is not present, you can be raising the voltage float on the secondary system due to capacitive coupling. Think of it as being in a ground fault loop in series with a capacitor.
Ground fault protection of a welding system would be a good idea. It can potentially be a difficult design to protect it, given the way it is used. But it would not be impossible. For example, the ground can be connected between primary and secondary, and a current sensor placed on it to check for any fault currents at the 4 milliamp level to protect humans. And additional current sensor on the actual welding leads could smooth out the current spikes first, and then see what difference remains.
transformer. You
touches
connected
What a lot of drivel. The OP said he put his wet gloves and person across the output which is probably 100 volts or some such with a current rating of MANY AMPS. No GFCI or other device will protect him from stupidity. It was designed to weld steel. it will most likely do a good job of welding a stupid person. If you can detect that the load is a person and not a piece of steel then maybe you can save him.
| What a lot of drivel.
Obviously you missed the point.
| The OP said he put his wet gloves and person across the output which is | probably 100 volts or some such with a current rating of MANY AMPS. | No GFCI or other device will protect him from stupidity. | It was designed to weld steel. it will most likely do a good job of | welding a stupid person. | If you can detect that the load is a person and not a piece of steel | then maybe you can save him.
So by using your reasoning, since it is possible for people to kill themselves by sticking their fingers in a light socket, or sticking paper clips into an outlet, then having ground wires and GFCI protectors for other more common modes of electric shock is not needed.
On 15 Jun 2004 08:55:09 GMT, snipped-for-privacy@ipal.net vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email
(1) but is not in the purview of earth fault cuiscuit breakers.
(2) one constantly stated advantage of trannies over other voltage reduction circuits, You cna _only_ get the volstage. SUPTA
*******************************************************Sometimes in a workplace you find snot on the wall of the toilet cubicles. You feel "What sort of twisted child would do this?"....the internet seems full of them. It's very sad
I've run into units in which the test switch trips the unit, but a GFCI tester doesn't. I don't trust the test buttons anymore.
Joel. phx
Had you considered the possibility that your GFCI Tester was defective, and the test button on the GFCI was functioning properly?
If you have the skills to work with live circuits safely (there is the potential for a lethal shock) you could construct a circuit that could tell you if the GFCI was functioning as intended.
With all live components insulated, and enclosed in a box you could assemble a circuit where a three conductor cord with the appropriate male plug on the other end was brought into the box with a 6.8k resistor connected to the hot wire to limit current to approximately 18 ma. The other lead of the resistor would be connected to a 100k pot. From the wiper of the pot a connection would be made to a shrouded banana receptacle. A second shrouded banana receptacle would connect to the ground conductor. With a multi meter connected to the banana receptacles, and set to the current mode you could read the current flowing in the circuit when plugged into the GFCI device.
With the pot adjusted to one extreme approximately 1 ma would flow. At the opposite extreme approximately 18 ma would flow. With nothing else connected to the GFCI except your test circuit (either the other receptacle on the GFCI, or to the load terminals) you could slowly increase the current flowing to observe where the device tripped. Recording that reading, and reconnecting the other loads to the GFCI would allow you to repeat the test and subtract to determine the approximate leakage of the load normally connected to the GFCI device. I believe a GFCI device designed for convenience outlets is specified to trip between 4 & 6 ma.
Measuring the current load your tester places on the GFCI circuit could also indicate it's place in the puzzle.
Louis
Another thought occurred to me after hitting send that could be your issue.
If the GFCI device were installed in a circuit where the ground was defective or non existent, it would operate as you describe. The test button on the unit would function normally, and the tester wouldn't (it needs the functional ground wire).
Louis--
********************************************* Remove the two fish in address to respond
needed.
I never said Grounds, GFCIs or any other protective system was not required. I just said you cannot protect a person from putting himself in place of the EXPECTED load. An this is what the OP did in the first place at the beginning of this thread.
Yes, except it was with a class of 12 who each had a tester (though not all checked). Good point on the ground, however the ground did appear functional, though a false ground is a possibility (although not probable for the year of the structure).
Joel. phx
I lit myself up pretty good one hot summer day, while laying in the bilge of an aluminum boat, while wearing only shorts and a welders leathers and welding underneath a brace below the steering gear. I grabbed the rod without gloves to change out the stub. My bare and sweaty back was in full contact with the hull..which was grounded to my workpiece.
Lincoln buzzbox, straight AC
Gunner
That rifle hanging on the wall of the working-class flat or labourer's cottage is the symbol of democracy. It is our job to see that it stays there. - George Orwell
Use a DC welder next time. That way if you ignore your heart's complaints again, you can defibrillate yourself.
Lie on the work clamp and touch the electrode to your chest. Reverse if your heart's DCEP.
Did that same kind of thing to myself once trying to finish a job after a rain started. Doesn't feel any too good, downright surprising.
Hmmmmn, there was supposed to be a smiley somewhere around here.
Gunner
That rifle hanging on the wall of the working-class flat or labourer's cottage is the symbol of democracy. It is our job to see that it stays there. - George Orwell
The GFCI circuit may have been ungrounded. External testers require a ground, or they will not trip the GFCI. The internal test button does not require a ground. The internal buttons are reliable, and there is no reason not to trust them.
Ben Miller
Benjamin D. Miller, PE B. MILLER ENGINEERING
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.