I have bought a cheap soldering iron. It seems to work fine.

Out of curiosity I tested the metal enclosure (and thus also the tip) with an electric tester and it lit up. Then I tested it with a multi-meter and it shows about 120V with respect to one of the mains and 0 with respect to the other. Mains is 220V where I live.

Then I tested the resistance between the metal enclosure end both of the power socket pins (it has only two pins, no ground wires.) It shows infinity. The metal enclosure gave no shock while connected, though I was heavily isolated from the ground.

I am interested in knowing what is happening.

My guess is capacitive coupling. Will I get a shock if I am somehow connected to the ground? Is the soldering iron ESD safe? If I ground the tip (and thus also the enclosure,) won't it trigger the ground fault detector?

  • 1
    \$\begingroup\$ It's capacitive coupling for sure. Try and measure the capacitance. \$\endgroup\$
    – Andy aka
    Jan 1, 2021 at 15:20
  • \$\begingroup\$ I am building my inventory from the scratch and right now I don't have anything to measure that :( \$\endgroup\$
    – Likhon
    Jan 1, 2021 at 15:25
  • \$\begingroup\$ When you write "the metal enclosure," do you mean the shaft of the soldering iron or a separate box that the soldering iron is connected to? \$\endgroup\$ Jan 1, 2021 at 15:34
  • 1
    \$\begingroup\$ Does it have a grounded mains plug? Is it connected to grounded wall socket? \$\endgroup\$
    – Justme
    Jan 1, 2021 at 15:40
  • \$\begingroup\$ Shaft of the soldering iron. No "earthing". Only two pins connected to the wall. \$\endgroup\$
    – Likhon
    Jan 1, 2021 at 15:52

1 Answer 1


It will be capacitive coupling if the resistance between the case and the supply pins is infinite.

It won't pass enough current to give you a shock (the burn will be much worse if you make the mistake of touching it). But it won't be ESD safe. That's why good quality soldering irons are grounded.

  • \$\begingroup\$ ESD grounding often involves a high-value resistor to ground. Would you suggest that in this case? \$\endgroup\$ Jan 1, 2021 at 22:15
  • \$\begingroup\$ I don't think the resistor is necessary. Anthing touched by the iron should already have had any static dissipated away. \$\endgroup\$
    – Simon B
    Jan 1, 2021 at 22:30

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