You pointed out that a 3-wire cord by itself cannot guarantee safety from electric shock, and I agree, of course. An improperly wired socket can be dangerous no matter what power cord you use.
In fact, my mother was nearly killed by a terribly mis-wired electrical outlet when I was still an infant - she went to get milk from the fridge for a middle-of-the-night feeding, and the entire metal body of the fridge was live, so she couldn't let go once she touched it. 😱 Fortunately my father heard some sort of inarticulate moan, and purely by accident, reacted in the right way to save her life: he picked her physically off the concrete floor, breaking the current flowing through her body. (He was wearing insulating bedroom slippers, so he didn't get shocked.)
But if your AC outlet is miswired, it's dangerous no matter whether you use a 2-wire or 3-wire AC cord. And in every other situation - with properly wired outlets - the 2-wire cord would be more dangerous than the 3-wire cord.
So I'll stand by my statement: "Two-wire cord no can defense!"
Seriously, no guitar amp should have a two-wire AC cord. It's just a terrible, terrible idea.
There are still guitar amps like this built today - toys like the Roland Micro Cube belonging to one of my friends. It's AC power supply is the usual tiny switch-mode wall-wart, complete with two-wire AC cord. The wrong electrical failure inside that cheap little wall-wart could put live AC voltage on the guitar strings. 😱
-Gnobuddy
A simple, quick, and safe test of an outlet that I've used is this.....
Get a good DVM, (I use my Fluke meters for this), set it for AC volts.
And for safety's sake, wear proper shoes or sneakers.
Insert one probe into the outlet ground/neutral slot, then pinch your fingers on the other probe tip.
If you get a reading of perhaps 3 or 4 volts, it's OK. - the outlet is wired correctly.
If you insert the probe into the "hot' side slot, and do this test, you won't be shocked, but it will read a lot more AC volts.
Of course, I've got one of those "3 light" plug-in testers as well.
Get a good DVM, (I use my Fluke meters for this), set it for AC volts.
And for safety's sake, wear proper shoes or sneakers.
Insert one probe into the outlet ground/neutral slot, then pinch your fingers on the other probe tip.
If you get a reading of perhaps 3 or 4 volts, it's OK. - the outlet is wired correctly.
If you insert the probe into the "hot' side slot, and do this test, you won't be shocked, but it will read a lot more AC volts.
Of course, I've got one of those "3 light" plug-in testers as well.
My mother saved me from an uncertain future when I was quite young. We had terrazzo floors in the house. These are a type of white Portland cement with tiny colored stone or mica flakes embedded in it, electrically similar to bare concrete. It was Miami, and we did not have air conditioning, so I was likely dressed in just a pair of shorts. The house was built in 1949, grounded or polarized outlets did not exist yet. At that time my authorized work space was a corner of her sewing room on the bare floor.
I had just rescued a hot chassis radio from some trash somewhere, brought it home and plugged in in. No glow from the series string tubes, so I ripped it out of its case, and plugged it back in. The last thing I remember was grabbing the chassis with both hands. The rest of the day was a fuzzy memory, but my mother was in the room when she heard a loud eruption from my mouth and saw me convulsing on the floor. Fortunately she was smart enough to simply rip the power cord out of the wall. That radio had one side of the power cord wired DIRECTLY to the metal chassis. What's worse than a death cap.....NO CAP! I would find several radios and TV's like this in my younger days. (early 60's trash, so the radios and TV's were 50's or older)
I recovered, and fixed the radio that almost killed me, then put it back in its cabinet and got some knobs for it. The incident also caused some damage to some of her stuff, so this got my authorized work space moved OUTSIDE, with my only power source being a 2 wire extension cord. Does it rain in Miami....almost every day in the summer.
My next rescue was a hot chassis TV set. That first incident and a few others led me to the knowledge of how the shocking experience happened, and how to prevent them. What I did then would still be considered STUPID today, but I am still here. Measuring, then marking plugs, cardboard, then finally plywood between me and the concrete, a light bulb with a probe on one side and a grounded water pipe on the other side....test before you touch......
About the time I entered high school my parents remodeled the house, and the garage became my bedroom, and we got air conditioning.....sort of. It allowed my workspace to move back into the house and expand. I also put a piece of plastic, and carpet between my feet and the concrete.
Yes, reverse bootleg is the secret shame of the electric testing racket.
A guy I know devised a much better tester. He started with UL, who were not used to gear which "requires" user contact(*) for a reference, and the UL fees would be far higher than the value of the musicians saved even if they bought it.
(*) So how does a NCVT work? Basically referencing the user's capacitive coupling to the average potential in the room. This tends to be groundy, but an exhaustively bootlegged electrical circuit could trend toward 120V off ground and befuddle this test. For-sure testing requires finding "real" ground and running long wires. This is only done after the accident (and usually not then).
A guy I know devised a much better tester. He started with UL, who were not used to gear which "requires" user contact(*) for a reference, and the UL fees would be far higher than the value of the musicians saved even if they bought it.
(*) So how does a NCVT work? Basically referencing the user's capacitive coupling to the average potential in the room. This tends to be groundy, but an exhaustively bootlegged electrical circuit could trend toward 120V off ground and befuddle this test. For-sure testing requires finding "real" ground and running long wires. This is only done after the accident (and usually not then).
I make it a point to wear good insulating footwear and to avoid touching metal parts with my bare hands. If I need to touch any metallic parts, I do it with only one hand, while making sure no other uninsulated part of my body touches anything. This means, if I touch a hot terminal, my whole body would be at that potential, with the consequence no potential difference is created between different parts of my body. This way, current cannot flow through my body and I am completely safe.
I also hold it as a rule to earth any electronic equipment enclosed in a metal box. Such an earth connection must be secure and reliable even in the event of a fault. Exposed metal must always be guaranteed to be at earth potential, otherwise it can be lethal.
I hate two wire mains operated equipment when such equipment has exposed metallic parts. A two pin plug can be inserted in two ways, which means, Neutral and Live would be interchanged. The latter is dangerous and stupid from a safety perspective. Live/Neutral metallic parts must always be insulated, so that, users would not be able to touch them.
I also hold it as a rule to earth any electronic equipment enclosed in a metal box. Such an earth connection must be secure and reliable even in the event of a fault. Exposed metal must always be guaranteed to be at earth potential, otherwise it can be lethal.
I hate two wire mains operated equipment when such equipment has exposed metallic parts. A two pin plug can be inserted in two ways, which means, Neutral and Live would be interchanged. The latter is dangerous and stupid from a safety perspective. Live/Neutral metallic parts must always be insulated, so that, users would not be able to touch them.