I'm have a low cost (<2$) soldering iron, similar to the one shown in the image, except that it has 3 plug terminals.


Suddenly something got me thinking about safety, out of curiosity I cut the wires, to find only 2 wires (I was expecting 3). I was wondering why I'm not getting a shock? I touched the metal heating rods and tips, nothing happened (with a tester first, of course). I don't find any isolation between the heating element and me. I'm guessing the neutral is wired on the outer side (which should be very close to ground potential).

The overall circuitry is just a diode and an led with 100k series resistor.

  • \$\begingroup\$ Why am I getting fownvoted? \$\endgroup\$ Mar 27, 2016 at 2:47
  • 4
    \$\begingroup\$ Of all things to spend some extra money on, I think soldering irons are at least top 10. A good quality temp controlled iron will last you for many years with good care. I've had mine work great for years. \$\endgroup\$
    – MichaelK
    Mar 27, 2016 at 4:13
  • \$\begingroup\$ Perhaps the tool simply omitted the ground connection, for a cheaper price?.... \$\endgroup\$
    – Brethlosze
    Mar 27, 2016 at 6:06
  • \$\begingroup\$ I've been using mine (WTCPN) for 3 decades and counting. It's just reaching a point where I might need to swap out a part. \$\endgroup\$
    – Ecnerwal
    Mar 27, 2016 at 15:47

2 Answers 2



simulate this circuit – Schematic created using CircuitLab

Figure 1 unearthed and, 2, earthed.

You are correct to be concerned. If a wire comes off the element or the insulation breaks down the case may go live. In the circuit of Figure 2, if enough current goes to earth the fuse will blow. An RCD or GFD will also offer protection.

Get a better iron.


You've obviously missed a few things. There should be a third wire going from your third prong to the sheath. It does not require insulation so you may have missed it. Here is a similar iron that someone has taken apart, although unfortunately with not much more attention to detail (the heater comments are not useful).

enter image description here

There pins on that piece of what looks like FR4 go into a heater that will be insulated from the outer sheath by some fairly high temperature material (mineral insulation or fiberglass or something like that). The LED indicator is incidental to the operation of the soldering iron- the heater does the real work and will be connected directly across the mains.

  • \$\begingroup\$ There should be a third wire going from your third prong to the sheath - I didn't find any, I tore 4-5cms of the wire. There were three prongs, both in the plug and also inside the soldering rod(cover). Another thing,Just to make sure I understand correctly. You mean to say that the heating element is completely isolated(electrically) and the metal part of the rod is just the heated metal, which is completely isolated. Right? \$\endgroup\$ Mar 27, 2016 at 14:35
  • 1
    \$\begingroup\$ The tip should be isolated from both current-carrying conductors of the plug. If there is a 3rd (ground) connector on the plug (and it is a metal one, not merely a plastic dummy or shutter actuator), then the tip should be electrically connected to that. \$\endgroup\$ Mar 27, 2016 at 15:06

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