Mac or Outlet, which side should be plugged in first?

[Blu101]

Skin resistance is a key factor and the current flow (amperage) depends on both voltage and resistance. Assuming resistance the same, voltage governs the amps that flow. Simple example: touch both terminals of a common 9 volt battery with your dry fingers. You feel nothing. Touch both terminals with your tongue, you get a tingle. Wet skin has a lower resistance. This is part of why 120V on dry skin is a pain but likely won't hurt you; 120V when you're soaking wet can kill. 220V gets a bit more dicey, as more current will flow across the same resistance.

Not quite. The original poster is correct. And even though your examples are also correct, in that lower skin resistance allows for more flow and thus, can kill you at lower potentials (voltages) - it's still the current (amperage) that kills you, not the voltage. In a way, you actually gave yourself the answer in your own examples...same voltage + lower resistance = more current flow = death. The reason why your tongue tingles from a 9V battery and your skin doesn't is because more current flows through your tongue due to its lower resistance compared to your skin, not the 9V, which remains unchanged. Bottom line, it is the flow of electrons (current/amperage) that kills you, not the potential difference (voltage). Typical electrostatic shocks are very high voltages, in the thousands (50,000 volts and higher are not uncommon), yet do nothing more than tingle whatever part of your body (usually your hand) is touching something else that causes the discharge (usually the door knob) - these don't kill you because they are very, very low currents.

 

[JamesGorman]

I always plug it into the wall first. When I first got my mac I noticed that if I had the magsafe plugged into the mac, sometimes when I would plug it into the wall, the outlet would spark. Ever since I started to plug it into the wall first, this has never happened.

 

[theaudioguy]

I have always felt that with all electronics you should plug into the wall first. That way any electrical discharge would be let out in the adapter first without traveling into the device.

but that's my opinion

 

[roliath]

Get a friend to help you plug them in at the same time. Like those guys turning the keys in missile silos.

lmao

 

[AllieNeko]

But then again, if there's a spark, and there is no grounding prong (like the US plugs) there is a chance you'll electrocute yourself as well as the macbook, since it's already connected.

But in reality, those things almost never happen. EU and UK plugs all have a grounding prong to prevent sparks and electrocuting yourself. US plugs don't have that, so the chances might be higher there.

US plugs ARE grounded. Grounds don't prevent sparks.

There are ways to prevent sparks (electrical arcing). In the UK, most outlets have switches to prevent sparks (plug in cord, THEN turn on switch). In the US, there are specially designed "hospital grade" outlets available designed to be resistant to arcing (necessary in a hospital due to oxygen use).

Connecting or disconnecting under load is what causes arcing, thus the nasty arcing you get when plugging in a switched-on high-current appliance like a vacuum cleaner. There is always some load on the MacBook adapter, and I've seen some small sparks on the outlet end (never the MacBook end) but never anything big.

 

[deeddawg]

it's still the current (amperage) that kills you, not the voltage.

I may not have been clear; it was your comment of "Volts has nothing to do with it" that I disagreed with; I agreed with "It's the amps that will kill you"

My point was that voltage does have something to do with it, since the amperage is related to both the resistance and voltage. Especially so when resistance is held constant as in the case of current flow when you touch different voltage sources (9V, 120V, 220V). Electrostatic discharge as you mention is a different case due to the relatively low amount of overall stored energy.

 

[Blu101]

I may not have been clear; it was your comment of "Volts has nothing to do with it" that I disagreed with; I agreed with "It's the amps that will kill you"

Wasn't my comment, it was brammp's comment I was just trying to help explain things for mutual benefit

My point was that voltage does have something to do with it

No, it doesn't.

We're talking about what kills you, not what controls the flow of current. Both voltage and resistance can be used to control/calculate the current, but it's not the voltage that kills, it's the current, and there's no two ways about that.

...since the amperage is related to both the resistance and voltage. Especially so when resistance is held constant as in the case of current flow when you touch different voltage sources (9V, 120V, 220V). Electrostatic discharge as you mention is a different case due to the relatively low amount of overall stored energy.

Yes, all 3 parameters are related to each other through Ohm's Law (E = IR), but this doesn't answer the question "what kills you".

Also, keep in mind that not all supplies regulate output through voltage (voltage regulators), as in the examples you mention. I say this because after reading your comments, I think that you think that a change in the voltage (or resistance) can get you into the kill range of current, and thus, voltage/resistance has "something to do with it". Sure, you can argue that they are *indirectly responsible* this way, but it's not the right way to look at it, because, again, it's not what actually kills you, which is what we're talking about. There are also current regulators out there, that regulate current output - here, a change in resistance changes the voltage, not the current (current is the parameter being regulated). The relationship still exists, i.e. a change in resistance with the same current changes the voltage parameter, but the voltage parameter is a result of the resistance and current, you can't control it directly (thus you can't say that it "has something to do with it" in these cases, because it is a function of the other two parameters), just like the current is the result of the voltage and resistance in a voltage regulator. Make sense?

Knowing the voltage can help though - let's say you don't know what the current is but you know it can vary depending on voltage and resistance (in other words, current is not being regulated), and you know the resistance (fixed/constant) - you can then calculate at what voltage the current flow will be strong enough to kill (again, it's the current that kills) so that, if the circuit/wire reaches this voltage, you know there's enough current to kill you and thus, you stay away from it (don't touch) and live (this can come in handy if you only have a voltage meter and no amp meter).

 

[AllieNeko]

Guys, do you realize that you both agree, both have a basic understanding of the concept, and are arguing about tiny, meaningless semantics?

 

[Blu101]

Guys, do you realize that you both agree, both have a basic understanding of the concept, and are arguing about tiny, meaningless semantics?

That's what working 40 hours a week does to ya

 

[deeddawg]

Guys, do you realize that you both agree, both have a basic understanding of the concept, and are arguing about tiny, meaningless semantics?

markie: you're quite correct.

Blu101: Thanks for the correction on the attribution, my error.

Actually, I was talking about voltage being related to current flow, not whether current "is what kills you" since I took that as a given. As Markie mentions, we're talking both sides of the same coin. I think the points relevant to this thread and to MR have been made, so I'm going to move on.