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In Reply to: RE: Two-Wire Cord is Extremely Hazardous posted by Triode_Kingdom on July 09, 2021 at 21:05:54
>> "The AC circuit is entirely isolated from the chassis.">> No, it's not. The schematic doesn't show the capacitance to the
>> chassis from any of the primary components. Most power transformers that
>> aren't hospital grade leak enough current to the chassis to kill a person
>> who comes between the chassis and ground. It's unconscionable to build
>> and sell a tube amp without a three-wire power cord.False.
The power transformer has a few hundred pF at most from one end of the winding to ground, which can pass an AC current in the microamp range. Modern safety standards allow 0.7 mA (below the "startle" threshold of about 1 mA, which could cause someon to jump or drop something) and well below a hazardous current. GFIs trip at 4-6 mA, a level considered hazardous. A typical voltmeter is 10 megohms, a cheap one one megohm; can show a voltage even when a non-hazardous current is available.
However, a kitmaker does not build and sell an amplifer; and cannot get safety approval since he does not build it. It would require a 3-wire grounded cord to gain safety approvals (or to be double insulated, which is not practical for the power transformer or output transformers).
Edits: 07/10/21Follow Ups:
Even if I was wrong (I'm not), what happens when the insulation deteriorates or there's an arc-over inside the power switch to the chassis? Only a third wire ground can protect the user from these and countless other hazardous conditions. Sure, you can trust your life to a Chinese interrupter. Not me.
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Buy Chinese. Bury freedom.
Your statement that transformer leakage could kill a person is false - it's minuscule. Yes, you can measure it with a voltmeter - but current is what's dangerous. This sort of design met safety standards for decades, though it would not today.
That said, I'm currently working on some amps from 1960 that have UL labels next to the (previous ) 2-wire cord. Now with grounded cords, like everything else I work on.
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