• (cs) in reply to Anon
Anon:

Since those are quotes of somebody else speaking, it is quite possible that Alex is fully aware of the difference between current and voltage, but that the speaker wasn't. Would you expect Alex to correct somebody's quote?

How cute! You must be new here.

Alex makes up just about everything in every story. You think some person sent him a full narrative written in the third person?! Alex has to rewrite everything he receives to make it fit the format of the site.

For all we know, the original story was about a circus clown who WTF'ed by locking the bearded lady in the same cage as the lions "in order to save a bit of money"...

• Azarien (unregistered) in reply to JuggaloBrotha

it's not as simple as that, depending on the country (and time) the so-called 240 volts can be anything between 210 and 250.

• Stinky (unregistered)

Computers have not needed that switch for nearly 3 years now. OR are the computers in europe designed with really low grade power supplies?

Every Dell I have seen and every PS I have bought from Newegg over the past 3 have not had that switch, they are auto voltage switching.. you can flip between 240 and 120 every 5 minutes and they dont care. Granted I have limited exposure. I only installed 600 dells and bought 120 power supplies in the past 3 years...

• (cs) in reply to Thg
Thg:
Yazeran:
Well technically you also change the current when you switch from 120 Volt to 240 Volt Especially if you put the same resistive load on :-)
Well, technically that doesn't make current the same as volts, or gravity the same as weight, or pressure the same as temperature.

But thanks for letting us know that you know V=IR.

Except you were thinking of P=IV, and besides, neither you nor he knew it, because you missed it when he went on to say:

In that case you get exactly 4 times the 'bang for the money' (2 for the voltage and 2 for the current) :-)
It's not called a power supply for nothing: when the voltage doubles, the current is halved.

I wouldn't ask an IT worker to fix my car, but sheesh! I thought there'd be some basic understanding of electrics. I'll never expect an IT worker to be able to change a fuse.

• (cs) in reply to Tharg
Tharg:
Folks,

I have to call BS on a few things here. First of all, most equipment that is expected to be able to work in numerous countries uses switch-mode power supplies (PSU). If adequately specified, and I do emphasise the "if" in that statement, plugging a U.S. based PC into a U.K. 240 Volt outlet presents no problem, other than plug form factor. The very nature of a switch-mode PSU protects both user and equipment.

There is no way to switch between voltages, so the story in that regard MUST be BS.

blah blah blah blah blah I don't get this shit blah blah blah

Well hey, aren't you Mister Whizzo Electrician?

So why do PSUs -- like the one illustrated -- have a little red switch on the back -- like the one illustrated?

Come back when you've learnt something.

• (cs) in reply to JuggaloBrotha
JuggaloBrotha:
Fuses and circuit breakers do the same thing
No they don't. Circuit breakers always follow the same spec. Fuses, on the other hand, once they've blown, get replaced with different amperage fuses, paperclips, rusty nails, and when they were still made in York, bits of KitKat wrapper.

By people like the majority of commenters on this forum.

• (cs)

TRWTF is that almost EVERY laptop adapter out there supports 100-240v, so the whole thing about execs bringing in US laptops should have been a non-issue.

Unless of course this happened years ago, before "world" adapters were common...

• Sou Eu (unregistered)

There's no standard voltage in Brazil. Indeed, different outlets within the same room may be different. To make matters worse, the outlets look the same and aren't labeled. Standard operating procedure is to plug in an inexpensive device and see if it works.

• (cs) in reply to JuggaloBrotha
JuggaloBrotha:
What I'm wondering is when someone will point out that it's 120v, 240v and 480v. A US house will run on 120v, a US factory is usually 120v and 240v for large equipment and 480v if 3-phase motors are involved.

Europe (and the rest of the world too) uses 240v in houses and factories with 480v in some factories.

3-phase would be 415V. 240√3 = 415.something. Note, this is 415V between any two of the active wires, and still 240V between an active wire and neutral.

• (cs) in reply to joemck
joemck:
TRWTF is that almost EVERY laptop adapter out there supports 100-240v, so the whole thing about execs bringing in US laptops should have been a non-issue.

My 486 laptop has a 100-240V power supply. I got it second hand in 1998 so that is well over a decade that these "universal" power supplies have been available.

My P166 laptop even came with a Japanese power plug (similar to the US but without polarisation or earth), (I bought this second hand in 2000) and the previous owner gave me an adapter. It worked fine for years (I'm in Australia so 240V) until I sold it to a friend. It used a started figure-8 on the PSU end so I had replaced it with a "standard" one. Unfortunately I accidentally sold that cable with it, then that friend moved to Japan!

• Sardonic (unregistered) in reply to Firethorn
Firethorn:
*With a few exceptions. They finally shut off the last DC distribution grid in NYC like 10 years ago, after operating for like a hundred years.

Even more recently (2003?) in Melbourne, Aus. Which for historical reasons had one of the oldest grids in the world.

The DC grid in Melbourne was finally shut off when someone dug through it, and it wasn't worth replacing. Instead, they placed semi-conductor rectifier stacks at every customer location, and connected up to the AC grid.

This means that scattered across Melbourne, (and probably Chicago and NYC) there are building which still have HV DC services. Mostly used for the Elevators/Lifts.

• (cs) in reply to Kaijuu
Kaijuu:
I have a small 100 volt grid in my house for my Japanese equipment, along with the regular 230.

Talking about Japanese equipment, the charger for my (Olympus) camera always seemed to stuff up: it would just start flashing the LED and it would not charge the battery until I reset it.

I took a holiday in Japan during the cherry blossom festival and the 100V there worked with my charger perfectly. And ever since then it has worked, even on 240V. So the couple of charges on the lower voltage seemed to have fixed it...

• Historian (unregistered) in reply to JuggaloBrotha
JuggaloBrotha:
What I'm wondering is when someone will point out that it's 120v, 240v and 480v. A US house will run on 120v, a US factory is usually 120v and 240v for large equipment and 480v if 3-phase motors are involved.

Europe (and the rest of the world too) uses 240v in houses and factories with 480v in some factories.

Actually, in the US it's quite often 110v and 220v.

A nominal 120 supply supplies 110 at the socket on a traditional system. (Modern systems may be more tightly regulated). You get 220v by using 2 phase-reversed 110v systems tied end-to-end (which was a traditional method of getting 220v in the US).

You also get 223v (which is close enough to 220 in a traditional system) by deriving the inverted phase from a star-delta connection on a 120v system. That's 120*1.87, which is what you get if you get the 220v from a substation,instead of adding 2 110v phases at the customer location.

• (cs) in reply to Rootbeer
Rootbeer:
A quick skim of http://en.wikipedia.org/wiki/AC_power_plugs_and_sockets doesn't turn up any plug designs which are physically compatible but use different voltages regionally.

Either this story has been anonymized past the threshold of plausibility, or the electrical WTFs in that warehouse are even worse than imaginable.

Oddly enough, in business environments in the US, I've never seen an electrician refuse to use a requested plug or socket type because it was the wrong standard for the power requirement.

That having been said, the last time I witnessed such a request, the electrician asked (when the PHB was distracted), "So are all of these systems redundantly powered?" The answer was yes.

Later that night, our monitoring server reported one of our power legs went away for a few minutes. Then, a few minutes later, the other one dropped for a few minutes. Years later, when we unplugged that cabinet, the plug and socket oddly enough matched the standard for 220, rather than being a 110 plug like we'd had originally and the socket to match. Not that we ever mentioned anything to the PHB who'd said to change the socket rather than the plug.

• Red October (unregistered) in reply to tgape

Could they have in fact been 20 amp plugs? The difference between a 20 amp 110V plug and a 20 amp 250V plug is which of the two pins is horizontal, and even though I know this I'd be hard-pressed to figure it out right away. 20 amp gear is something else that is, for whatever reason, frighteningly uncommon. If you live in the states in a reasonably modern home, You probably have circuits in your house capable of serving it, but only lack the sockets (which usually have a T-slot to accept 15 amp plugs as well.) It also could have been done deliberately as an anti-tamper measure, so that someone unplugging the server would be presented with a useless socket for anything but the server, to discourage them plugging in their radio/kettle/personal massager/floor buffer. If that was the goal the Electrician should have used a twist-lock plug of the correct rating, rather than a plug rated at 220V, which, while not creating an immediately hazardous condition, created the ability to connect the server to a 220V plug elsewhere. I suppose someone might have asked for anti-tamper and the electrician used what he had on hand, thinking there was no harm to an up-rated 110V socket and a presumably several-hundred-pound server with a 220V plug that was unlikely to be moving. It could even have had a switchmode power supply which could cope with 220V if it were presented with such, in which case there was no harm at all.

CAPTCHA "eros". Ther server is horny.

Also, I though it was standard practice in the Europe for power runs to be loops where each end is connected to the service panel. The would really complicate sticking in a step-down transformer that you can switch in and out.

Nope they are mostly used in Britain and sometimes in Ireland. Germany generally uses a star-topology as do the other continental countries.

• (cs)

To everyone saying "Oh the story is fake cos computer/laptop power supplies can take any voltage",

STOP ASSUMING THE STORY IS RECENT.

Quite often the stories posted here happened years ago. After all, despite the anonymisation, the tellers might still have kept quiet until the left the workplace it happened at.

• wtf?! (unregistered)

Reminds me when I was in college, and had switched my 386 from 120 to 240. I too didn't have a clue about electrical standard at the time, and hey! 240v is probably way better than 120v.

Fortunately, my 386 ran practically normally in this setting (switched to 240v and plugged in 120v plug). The only annoyance I had was each time my dad was turning on the outside lights of the house, the 386 rebooted.

Later on I wisened up and flipped the switch again... and never touch those switches again.

• (cs) in reply to m0ffx
m0ffx:
To everyone saying "Oh the story is fake cos computer/laptop power supplies can take any voltage",

STOP ASSUMING THE STORY IS RECENT.

Quite often the stories posted here happened years ago. After all, despite the anonymisation, the tellers might still have kept quiet until the left the workplace it happened at.

Oh yeah, because switching power supplies and line fuses are recent developments.

• (cs) in reply to frits
frits:
m0ffx:
... STOP ASSUMING THE STORY IS RECENT. ...
Oh yeah, because switching power supplies and line fuses are recent developments.
Just because they were invented millions of years ago does not mean they were in broad use a couple of years ago.
• Ron (unregistered)

Don't forget, we do use "220V" here in the States... your dryer and stove outlets, as well as say at my parents where my dad installed a 220V outlet in his garage for his welder...

• Mayhem (unregistered) in reply to hallo.amt
hallo.amt:
frits:
m0ffx:
... STOP ASSUMING THE STORY IS RECENT. ...
Oh yeah, because switching power supplies and line fuses are recent developments.
Just because they were invented millions of years ago does not mean they were in broad use a couple of years ago.

Almost every cheap PSU sold in australasia in the 90s was fitted with a 110-230 switch at the back. I remember the CS department at my highschool going ballistic at some kid who delighted in swapping them round before the class would start. Since NZ runs on 230V, setting it to 110 would result in a hefty bang on a regular basis and a suitable disruption to the lesson. Switchmode supplies only really started spreading around 2000, before that they were too expensive. And I can remember my old mans laptop had two power bricks, a 110 and a 230, although that thing was ancient, from mid 80s.

paratus - always prepared for malignant users

• Cees de Groot (unregistered)

15-ish years ago, me and a colleague got invited for some coding workshop at Microsoft. Not having a laptop and refusing to work on Windows, I checked the back of my DEC Alpha OSF/1 workstation, verified I could set it to 110V, and put the whole thing in my suitcase.

Great decision, I could work like at home over at Seattle, and I had a fun two weeks.

...until I got back, retrieved my workstation from my luggage, plugged it in, flipped the power switch, and heard a small bang announcing some expensive repairs to the fried power supply that was still on 110V, of course.

• Yazeran (unregistered) in reply to rfsmit
rfsmit:
Except you were thinking of P=IV, and besides, neither you nor he knew it, because you missed it when he went on to say:
In that case you get exactly 4 times the 'bang for the money' (2 for the voltage and 2 for the current) :-)
It's not called a power supply for nothing: when the voltage doubles, the current is halved.

I wouldn't ask an IT worker to fix my car, but sheesh! I thought there'd be some basic understanding of electrics. I'll never expect an IT worker to be able to change a fuse.

Actually I did include the assumption that it was a resistive load. Yes I know switchmode powersupplies are not resistive, but some older powersupplies are (old transformer-types with big power-transistors for voltage control). They are still used for some applications (NOT PC's) where the high frequency noise from a switchmode powersupply is undesirable.

• spacecoyote (unregistered)

Mid-range and low end PSUs like this one aren't auto-sensing.

• anon (unregistered)

One nasty property of those switches at the PSU's is that by turning them to 120v then plug them in a 230v one, you can easily blow them up.

• Eric the Reddest (unregistered)

"“Since the executive comes from the US, he cannot plug into the 240 volt outlet I normally use. Because they forget their power adapters so often, we just put in a few switches that allow electric currents to be changed for the entire electrical group.”"

...because this happened in the early 80s and laptops didn't have 100-250V rated adapters?

It's still a nice story though.

What makes this seem a bit incredulous is that industrial applications often times have home runs for each outlet, especially in areas where people may plug in high draw equipment. Even if that wasn't the case, the entire factory floor couldn't be running off a single circuit. Each circuit would require its own step-down transformer.
NewBee:
This story doesn't make sense if an American is visiting a 230V only country because it would be very expensive to make a 120V circuit just for a visitor.
Tharg:
There is no way to switch between voltages,

Actually, I've seen this type of refit before. You take a DPST knife switch, an existing centertapped 240V (0*/180* 120V) mains transformer in a factory and make the following connections: (180*) to one postion of the DPST, (center/neutral) to the other- run the 0* as your live and the common terminal of the DPST switch as your neutral. This results in a cheap (as free) 120/240V mains switch poised to make some sparks-

An even though it would cost perhaps an additional \$500 in materials to run seperate neutral/180* lines to deliver BOTH 120 and 240V from teh same transformer, this would require not reusing the existing factory wiring.

And befote you say "When was the last time you could walk into an abandoned factory and expect to find a mains 120/240V center-tapped-transformer and knife-switch?", "1988." These days its all threephase +300V this or that and I don't want to think about how you would jury rig 240V/120V out of that...

^ - -^ MEow.

• NeoMojo (unregistered) in reply to Anon
Anon:
Thg:
Anon:
Bob:
"...we just put in a few switches that allow electric currents [sic]..."
"I am one of the few that cannot change current [sic] on the PC itself."

Since those are quotes of somebody else speaking, it is quite possible that Alex is fully aware of the difference between current and voltage, but that the speaker wasn't. Would you expect Alex to correct somebody's quote?

problem solved

I did consider suggesting the use of [sic], but then I remembered that only arrogant douchebags would insist on pointing out everybody else's mistakes in such a passive aggressive way.

Much better to use "I am one of the few that cannot change current [retard] on the PC itself." Then you are being plain old aggressive.

• Anonymous (unregistered)

It was an accident waiting to happen. That happened.

• arrogant douchebag (unregistered)
only arrogant douchebags would insist on pointing out everybody else's mistakes in such a passive aggressive way.
Very subtle, I like it. Lost some possible friends using that sort of humour though.
• Maurice (unregistered) in reply to ih8u

err I think he meant a propper time served Electrician (and presumably bonded) who has done a proper apprentiship and a proper HVAC one at that.

dont confuse a proper trade with a+ certs

• JB (unregistered) in reply to Historian
Zemm:
3-phase would be 415V. 240v3 = 415.something. Note, this is 415V between any two of the active wires, and still 240V between an active wire and neutral.
I realized after posting that I didn't have that quite right, 3 phase isn't as common in the US other than large factories so I'm not as in tune with it as I should be.
Historian:
Actually, in the US it's quite often 110v and 220v.

A nominal 120 supply supplies 110 at the socket on a traditional system. (Modern systems may be more tightly regulated). You get 220v by using 2 phase-reversed 110v systems tied end-to-end (which was a traditional method of getting 220v in the US).

You also get 223v (which is close enough to 220 in a traditional system) by deriving the inverted phase from a star-delta connection on a 120v system. That's 120*1.87, which is what you get if you get the 220v from a substation,instead of adding 2 110v phases at the customer location.

In Michigan, USA (where I live) the code is strictly 120v/240v, if you have 110v you're out of code and should have the transformer checked. If it's outputting 110v it's a sign the oil's either leaking or goign bad which creates a fire hazard.

• Red switch guy (unregistered)

Hello, this is the guy known in the story as "Byron Schield" - a fake name to protect my real name from being linked to this incident.

Seeing the comments i think i should clarify a few things:

1. First and foremost i have no training in electronics whatsoever. Errors with voltage and current, among with some of the inconsistencies might originate by my own lack of understanding about the subject.

2. The factory building we are talking about had been empty for a real long time with no maintenance whatsoever. My former company moved in almost before the most critical repairs were completed, and even the things that were done had been done hastily. From what i heard almost the entire electrical infrastructure had degraded to a pure hazard zone over time.

It is possible that the speedy repairs were goofed up or only partially complete. Maybe my switch flip wasn't directly responsible for the incident. For example some offices on the third floor were unused because there were leaks in the pipes there. Maybe something such as this was related. Perhaps switching two switches at once caused a short circuit or anything. I know to little of electronics to say anything with certainty.

All i know for certain is that around 50 PC's died with a huge bang, right after i flipped those switched. Other then that i can offer little insight into the how im afraid. But one thing was for certainly true: The entire place was a complete and utter mess on many levels.

• (cs)

Hahahaha that's great :)

• Graeme Hill (unregistered) in reply to expat

I can remember in Saudi having little step-down transformer boxes with meters so we could run our 110V equipment off 240V supplies. [and vice versa]. It really was a pain in the ass to set things up. I managed to blow the power supply fuses on an IBM minicomputer that way....

• Graeme Hill (unregistered) in reply to hallo.amt

Known as a "Ring Main"

• FFS! (unregistered) in reply to rfsmit
rfsmit:
JuggaloBrotha:
Fuses and circuit breakers do the same thing
No they don't. Circuit breakers always follow the same spec. Fuses, on the other hand, once they've blown, get replaced with different amperage fuses, paperclips, rusty nails, and when they were still made in York, bits of KitKat wrapper.

By people like the majority of commenters on this forum.

That may happen if the design of your fuse boxes is retarded. If they're properly done they will only accept a smaller than specified (by the electrician) fuse.

So how about realizing that not every country has such a retarded system as the UK does. Retard.

• Max L (unregistered) in reply to operagost

I wouldn't bank on surge protectors in a generic piece of electrical equipment kicking in at 330V.

Apparently even the super cheap power strips do have MOV surge suppressors but they suppress surges less than 220V. Since they are surge suppressors running a constant over voltage induces them to melt and smoke until the breaker trips. The surge suppression elements now form a 0V surge suppressor, AKA short circuit, and cause more smoke when plugged in anywhere else.

The moral is don't assume that a power strip is just a switch and bunch of outlets even if you only paid \$5 for it. I never bothered to buy another strip and cut out the MOVs but I'm pretty sure it would work and it would mean only having to carry one plug adapter or at worst one UK adapter, one Euro adapter and maybe one for Italy.

Max L.

• BSEE holder (unregistered) in reply to Crash Magnet
Crash Magnet:
Pedantic:
Zapp Brannigan:
nB:
that would be E=IR, not V=IR
I don't get the nuance of E vs V. Could you explain?

E = Electro-motive force.

I would think its a mater of convention. EE students learn to write their answers like:

``````E = 12V
``````

``````V = 12V
``````

which look kind of wierd. This also pulls in the reason EE's lean to use j for the complex operator because they use I for current. They learn to write:

``````i = 12j mA
``````

``````i = 12i mA
``````

it just looks wierd. That an the fact that there are millions of EE's who to it one way and will kill you if you try to do it the other way. It's a standard convention.

I call bullshit. I am an EIT and a holder of a BSEE degree from an ABET-accredited university in the US and here we write Ohm's Law (and voltage calculations with a V)

We use "E = " when calculating energy. Like the amount of energy that a capacitor can hold.

• BSEE holder (unregistered) in reply to frits
frits:
Coyne:
frits:
I call BS. There is this thing called a fuse in every piece of electrical equipment that plugs into a wall outlet. For those of you who don't know, they are designed to break the circuit before damage occurs from overcurrent conditions.

Fuse slooooooowwwwww. Overvoltagedamagereallyfast!

This diagram shows that a 20A "fast-acting" fuse can carry 100A for up to 0.1 seconds before blowing.

So the power supply is long dead before the fuse can react. A capacitor can blow after 1/2 cycle of current (0.008 second)...it only takes that one pulse of voltage over the capacitor's rated maximum, and it's toast.

The fact that you chose a 20 Amp Bussman fuse as a line fuse for a PC invalidates your post.

Addendum (2010-01-06 08:39): I'd like to know where you get this from :

"A capacitor can blow after 1/2 cycle of current"

Most capacitors can take several seconds of gross overvoltage before overheating and failing. The voltage rating for capacitors has a built-in safety factor and is specified for continuous use.

I have not designed switching-mode PSUs, but from what I understand, overvoltage causes the solid state components to fail. Thus a mere fuse will not act fast enough to save the power supply.

• ChrisKC (unregistered) in reply to BSEE holder

I'm sure it's not to code (though what they did surely isn't either), but why not just run the ~230v to the rooms, then install some ~115v using just one of the ~230 lines and ground? Granted, this requires three-wire cables, which may not be what they were using.

Just make sure the outlets are different and appropriate for each voltage.

That way, you can have both 115/230 in every room at the same time!

• Eino (unregistered)

The reason why computer power supplies readily go bang when you flip the switch to 120 volts and then connect to 240 V, is because the actual circuit in the power supply defaults to 240 Volts, and the switch connects the mains through a diode pump voltage DOUBLING circuit, generating 480 volts into the primary tank capacitors used to level out the rectified current. The absolute maximum the capacitors will take is about 400 volts, for a few seconds. The voltage doubler circuit is also responsible for the ~5% efficiency loss when running at lower voltage.

The actual transforming circuit is optimized for roughly 220-240 volts, and cannot run properly at a lower voltage. Modern multi-voltage power supplies simply do the switching automatically when they detect a lower voltage, which is why, even though the face plate says so, it won't run at just any arbitrary voltage between 90-240 V. There's a crossover point where the power supply will switch to doubling the voltage and that can have catastrophic consequences if the input varies in case of a brownout for example.

And the British obsession for fuses in the plugs is due to the use of ring wiring, where a thinner cable is used, and is wired to the fusebox at both ends, but in a case of failure on a device the fuse wouldn't easily burn because a bigger fuse must be used to supply all devices in the ring.

The main fuse in the ring is therefore used against overload conditions instead of device failures, and this system is actually more likely to overheat the wires in the walls in the case that the ring is cut because the effective cross sectional area of the wire is halved, but power is still running to the connected devices on both sides of the cut. There is no way to know if the wiring has been compromized, which is why old houses can be real deathtraps.

The continental style where each non-looping branch is protected by a single fuse is sized so that the fuse will only let through as much current as the wire will handle safely. If the wire branches, the same diameter must be used all the way up to the socket.

Because the fuses are smaller, a device failure also trips the mainbox fuse, though the required current is somewhat higher than with the UK style plugs which are slightly safer in this respect. In any case, since the required current is several amps the effect is mainly to protect against fires and having the casing of the device go live. A person on the line won't trip a fuse - for that you need a fault current switch. (Which is not the same as the circuit breaker you'll find in modern installations. That is just a reusable fuse.)

And of the E vs. V issue. Some places use U for voltage/EMF, because E is typically reserved for Energy in physics, and V is for Velocity.

• Sidecutter (unregistered) in reply to Renan "C#" Sousa

Yes, and most computer equipment power supplies, these days, use active PFC in the power supplies. It handles the different voltages by automatically sensing the correct one and switching itself over, which is why they lack that little red switch anymore.

But we don't know when this story took place, and for cost reasons, it wasn't until that last five years or so that active PFC really became "standard". Especially in budget gear like many companies rely on for their workstations.

• Morgan Creighton (unregistered) in reply to Rick
Rick:
Mason Wheeler:
Rick:
But seriously, 220v is more dangerous than 110v. You were lucky. Electricians, users and product manufacturers are more careful with 220v. Not that it would ever happen, but if the US were to convert to 220v for household current there would be many deaths, while all 3 parties were educated.

Really? I'm no electrician, but I have a friend who is, and he told me the exact opposite once. He said that 220 may hurt more than 120 because it's higher voltage, but it's actually less likely to actually kill someone because double the volts means half the amps.

Third post attempt...

Please get a third opinion before you touch wires.

Mason Wheeler:
Rick:
But seriously, 220v is more dangerous than 110v. You were lucky. Electricians, users and product manufacturers are more careful with 220v. Not that it would ever happen, but if the US were to convert to 220v for household current there would be many deaths, while all 3 parties were educated.

Really? I'm no electrician, but I have a friend who is, and he told me the exact opposite once. He said that 220 may hurt more than 120 because it's higher voltage, but it's actually less likely to actually kill someone because double the volts means half the amps.

Third post attempt...

Please get a third opinion before you touch wires.

To be more explicit, the formula E = IR has been mentioned here a number of times. In English, Voltage is equal to Current times Resistance. If the resistance of your body remains constant, then if voltage is doubled, current will also double. Your electrician friend may not be as good a friend as you thought.

Addendum (2010-01-05 15:08): And thank you Mason for validating my point about the need for education.

No, the electrician friend was correct. 220 is slightly less dangerous than 120 because it's not the amperage that kills you. It's the fibrillation of your heart that kills you. Fibrillation is when the muscles contract and relax out of sync, and the heart can't pump. A higher voltage locks up the entire heart, so when the current stops, the muscles are all still in sync, and can resume beating in coordination.

But for humans, 120 volts lies in an uncanny valley of danger. Smaller and larger voltages are less risky, because exposure to 120 knocks the heart muscles out of sync, so you suffer a heart attack when the current stops.

In hospitals when doctors defibrillate heart attack victims with those electrical paddles, they are applying a high voltage (typically 300 or more) to sync up all those heart muscles. In the movies, they make it seem like they are restarting a stopped heart, but that's just Hollywood.

Citing E=IR is a spherical cow. Biological systems are rather more complicated.

• Trident (unregistered) in reply to JuggaloBrotha

Well this is not entirely true.At least for 400V(380V in the past) for europe. In some countries in the europe is technically impossible/rare to get three phase 400V. This is reason why many heavy duty equipment imported from abroad like a circular saws or A/C units i see with simple 230V socket(s). Anyway for high power demanding devices high voltage(standard differs across countres, in CZ is 22kv) connection is required together with own transformer substation to low level 230V. On the other hand in Czech republic almost every electrified home can have three phase power. Many electric ovens, heating pots, motorized equipments etc. are using this 3p power. 3p power also gives you possibility to balance power load across phases in your home. Cables are there even in old installations and in most cases unused cables and fuses are waiting to be used. On the other hand from my colleague i know that in UK is trouble to get three phases, because many homes are connected only by one phase from the street distributors.

• QBall (unregistered) in reply to Alargule

Oh yeah. When I was in elementary school I learned about these switches. One time the class was doing something in a computer lab and the kid across from me couldn't get it to work (was doing it wrong). The teacher came over, and jokingly offered to bet him \$50 that it would work when the teacher did it. Right when the teacher did it, I flipped the red switch to the other setting and then back, causing the computer to reboot. I had difficulty containing laughter.

• 🤷 (unregistered)

I learned of the little red switch as a kid, too. The computer wasn't working anyway, so I decided to look at the innards of that "magical computer thingy", after looking around for a bit I saw that switch on the backside of the power supply. So, I switched it, just to see what happened. Turns out, power supplies REALLY do go out with a bang.