I am currently rewinding 2 microwave transformers to create an electrical arc furnace. I have taken the secondary coils out of each transformer and am planning on winding new ones. In theory the device should output about 200 amps at 36 volts. I got the idea from a series of youtube videos, links to which are below. The guy, who seems experienced with this kind of stuff, is using 8 gauge wire to wind his secondaries. I have purchased raw 6 gauge stranded copper wire. I have wrapped all of the wire in 3 layers of electrical tape (the hardware store didnt sell insulated). However, a quick google search indicates 6 gauge wire is only safe to use up til 55 amps. Even with the two transformers, each would be handling around 100 amps, which is almost double the amount the wire is rated for, yet this guy somehow pulled it off reliably with 8 gauge wire which only supports 40 amps.

A few questions.

  1. Would operating this device burn my secondaries if using continuously for only brief periods of time?
  2. Is using electrical tape to wrap the wire a bad idea?
  3. If using electrical tape is a bad idea, how would you recommend an alternative safe insulation method?

I recognize the obvious dangers and lethality of this project, however i have taken precautions and am attempting to inform myself to avoid any accidents.

Youtube Links:

  • \$\begingroup\$ That guy built an arc welding rig. You can use it intermittently without it overheating. An arc furnace has to run continuously, though. It will get hot and burn up on you. That's the difference. Even professional arc welders aren't intended for continuous operation - there's usually some expectation that you make occasional breaks, during which time the coils can cool off \$\endgroup\$
    – JRE
    Jul 16, 2018 at 11:20
  • \$\begingroup\$ The third video says it's about an arc furnace. Couldn't get it to play - loading time is too long on my phone. \$\endgroup\$
    – JRE
    Jul 16, 2018 at 11:24

1 Answer 1


You can get a high temperature braid that you can use for the insulation or source a cable with high temperature rated insulation : do NOT use that electrical insulation tape...

What precautions have you taken / are you planning, because at the moment I would suggest that you should NOT plug this in at all...

  • \$\begingroup\$ Will do. Im not plugging it in until i know everything will be running smoothly. Both coils are wrapped with many layers of electrical tape, so no contact with core or each other. I have purchased insulating gloves apron etc to protect me. The handles of the vice grips i am using to hold the electrodes are also well insulated. The arcing is occuring within firebrick, so the heat/electricity is contained. I am planning to install a kill switch should things get out of hand. My only concerns are the coils overheating and the insulation on secondaries. Any extra advice for safety/insulation? \$\endgroup\$
    – john doe
    Jul 16, 2018 at 23:19
  • \$\begingroup\$ As @johndoe states, I see quite a few safety issues. 1) The maker of the video used two separate 120 V lines, rather than a correctly-sized 240 V line. 2) At 36 VAC, 200 A, this will draw ~7 kW! Ordinary 120 VAC home wiring is not able to handle that. 3) There is no ground for the transformer core. Should the primary insulation break down, or a wire come loose, this could but full line voltage on the transformer. 4) Toxic fumes are produced. 5) The fire danger is obvious. Home testing hand grenades would be safer. \$\endgroup\$ Jul 17, 2018 at 0:04
  • \$\begingroup\$ @drmoishepippik i have done some calculations, and it seems to me that this device takes in 30 amps and 240 volts. Ive read that a typical wall outlet provides about 15 amps. What the maker of the video did is he used two wall outlets, hence the 30 amps. Am i correft in my assumptions? Toxic fumes can be produced from melting metal yes, but i am going to be wearing a mask. Im going to buy a fire extinguisher for the fire hazard, thats a good point. As for the 240 v line what would be the appropriate size? Will my home wiring be able to handle the power requirements with two wall outlets \$\endgroup\$
    – john doe
    Jul 17, 2018 at 1:30
  • \$\begingroup\$ No, the two outlets are in series, and could provide no more current that way. Also, should one circuit breaker trip, that line would be fed 120 V through the transformer, and would still be live. Ask an electrician about what you intend. \$\endgroup\$ Jul 17, 2018 at 2:54

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