What's wrong with my answer?

Question

This has got two downvotes:

https://electronics.stackexchange.com/a/54982/16047

The mouseover for the downvote says "not useful", however I thought it was very useful! :/

Is it just because I actually qualified DC rather than saying they're both bad be careful like everyone else?

Answer 1

I did one of the four dowvotes, but I also explained why in a comment. Personally, I reserve downvotes for answers that are misleading or just plain wrong. I was bothered by your incorrect use of "RMS", so much so that I felt your answer was misleading. By giving your answer a negative score, it provides a strong clue to others not to trust the information in it.

I see you have reworded it a little, but there are still errors or at least misleading use of terms. Currently, my objections are:

1. You say you are assuming the original question was not using implied RMS for the "230 V 50 Hz AC" in the question. That is such a bad assumption as to be wrong. Both the 230 V and the 50 Hz part make it clear that this is the power line voltage, probably what comes out of the socket wherever this OP lives. By saying that you assume it is not RMS, you are creating confusion. If you want to make the point about RMS versus peak or peak to peak, that's fine, but do so as a add-on since the whole point is likely beyond the OP's level of understanding. I also pointed out that RMS was clearly assumed (even if the OP doesn't know the difference) in this case in a comment, so you can't say you weren't aware of this.

2. You are still using terms incorrectly to the extent they could easily confuse someone. You say you assume the AC voltage is the signal amplitude as apposed to RMS. What exactly is "signal amplitude" supposed to mean? Without specific qualification, the first assumption would be RMS. Someone being on shaky ground with this knowledge could think they learned something from this statement that would be incorrect. They could take away "Ah, signal amplitude doesn't mean RMS", when in fact usually it does.

3. The part about holding a stripped power cord in your hands and not dying is also incorrect. If you had qualified that by saying in a single hand, then I might agree with you. However, you actually mention "hands", so one can assume you meant one lead in one hand and the other in the other hand. 230 VAC certainly can kill you like that since the current runs thru your chest close enough to your heart. People have died for touching 230 VAC the wrong way. That stuff is dangerous. That doesn't mean you will always die, maybe not even most of the time. But death is likely enough, and has happend enough in the past, to make your statement wrong and potentially dangerous to someone that doesn't know better.

I can't tell if you are just being sloppy, know you're being a little loose with the terms but don't care, are have a real misunderstanding of RMS, although I'm starting to suspect the latter. If you fix these things and ping me in a comment, I will undo my downvote.

Answer 2

I am sorry to say that the reason you are being downvoted because your answer in general has some true pieces but is overall bad advice. This is my opinion and it is the opinion of others in the community, which is why you are receiving downvotes.

Some examples:

If you plug one end of an extension lead into the wall and cut off the extension-plug end and strip the wires and hold on, you won't die (but will get black marks on your hands).

This is scary to me, wall outlets where I am are 110V AC and operate at nearly the same frequency as a heartbeats. It is very possible to go into fibrillation from wall outlet power.

You have already had the RMS point brought up in comments, but power from powerline is always specified in RMS. If someone says they have 230V line power it is 230V RMS, so the DC having less power is not valid.

Power is transmitted over high voltage lines

Not even sure how this relates to the current kills, voltage doesn't. High voltage power lines dont give a second chance, the scariest thing at my job is the 15kV generator. It can deliver 18A. You are correct that just high voltage without current is not very dangerous, but the opposite is true also. I have a 250A power supply for 3V, that supply does not worry me either. It really takes both, the reason people saying that is because once you have enough voltage to conduct a large current the current reduces your resistance and runs away. I was once told, "Always have an observer when you work on the power supply, that way someone can warn you before you do something dumb, if you do something dumb you are already dead."

The only thing I will agree with is that with DC you cant let go. You are very correct, but if I am going to pick between burns and my heart stopping I will pick neither.

@exscape, yes: it works for any frequency.

This is also not true, when you get to higher frequencies it will just cook you. It works for frequencies at a low enough frequency that your body reacts to it. 10kW RF would just cook you, there would be no two ways about it, but you would have muscle control the whole time, if that makes anyone feel better.

This answer seems pretty good.

Answer 3

The answer as it stood had a few misleading/inaccurate points. Also since it relates to "high" voltages, people will usually take any mistakes more seriously, since many inexperienced people read these answers and may accept the information given without question. The part that bothered me the most was the idea of grabbing on to a live wire with both hands.

Olin's answers puts the main reasons well, so I won't go over then again. Now you have reworded the answer, I feel happier to let my upvote stand now.