I noticed the tip of my soldering iron is case grounded. I understand the GFCI compares voltages and trips if there is a difference (in the millivolt range). If the thermocouple generates a small amount of voltage, can't it trip the GCFI? Moreover, what does the GFCI use as a voltage reference?
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2\$\begingroup\$ It's not voltages that the GFCI/RCD is measuring, it's currents. It trips if there's a difference in the currents on the live and neutral wires. \$\endgroup\$ – Hearth Feb 5 at 17:52
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\$\begingroup\$ Could you post a model number of your soldering iron, please? I'm curious about its grounding. \$\endgroup\$ – Nick Alexeev♦ Jun 22 at 22:47
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I understand the GFCI compares voltages and trips if there is a difference (in the millivolt range).
Actually, the GFCI compares current (in the "line" and "neutral" wires) and trips if there's a difference of more than a few mA.
If the thermocouple generates a small amount of voltage, can't it trip the GCFI?
No, the thermocouple (if your iron even has one) would be unrelated to this.
Moreover, what does the GFCI use as a voltage reference?
A GFCI does not need a great deal of precision, so it probably just uses a diode junction as a voltage reference.
