AC and electrocution?

[jeff262]

As i have said before my knowledge is totally limited to DC. The current project I am working on requires me to use 120V AC. I was curious if both sides of AC are equally dangerous? I have to use a cutoff wire to run thru a float switch and was curious if one side is better to use then another if some reason the float fails and allows water in making a short. Someone said the common wire but this guy also has 4 of his finger nails black from being shocked way to much off of 240V
thanks jeff

[Chatenever]

On a standard 120V circuit, the black (hot) wire is under 120 volts of electrical "pressure". The white (neutral or common) wire is close to zero volts of pressure. You will get a shock if you touch the Hot wire, but touching the neutral wire should not be very exciting. On building wiring, codes require that you place switches in the Hot leg for safety considerations. Switching the neutral leg will turn off the load just as well as switching the hot leg, but there is no advantage to switching the neutral, and there are certainly some safety disadvantages.

FYI, on 240V wiring, depending on the transformer from the power company, you most likely have two Hots, each one 120V relative to a neutral or ground. However, they are 180 degrees out of phase with each other, so the voltage between them will be 240V. On SOME 240V systems, you may find one of the hot wires is actually 240V relative to ground, while the other side is the same as neutral. Normally, BOTH legs are switched off to de-energize a load.

[ghoti]

1) wear rubber shoe soles
2) keep one hand in your pocket
3) anything greater than 50 volts, AC or DC can kill you

[indtech]

use a ground fault interrupter

http://en.wikipedia.org/wiki/Residual-current_device

[pilotpete2]

Hi Jeff,
Take Indtech's advice and use a ground fault interrupter :)
Secondly, if at all possible if working around electricity keep your left hand in your pocket, just in case you do get a shock by being grounded through your feet, always a danger when standing on a concrete floor, like in the basement. As you're not an electrician, any "rubber sole" shoes you may own cannot be considered safe if working in a damp area or outside on the ground ;)
If I lived in a Country where 240AC is used (referenced to ground) I'd be dead :eek:
Pete

[infopimp]

I've heard keep your left hand in your pocket. Otherwise it will go through your heart on the way to ground.

[MarkusN]

If I lived in a Country where 240AC is used (referenced to ground) I'd be dead :eek:
Nope, you wouldn't. 99 out of 100 cases a 240 V electrocution is just a (hurtful, I give you that) buzz.
If 240 V invariably killed, I wouldn't be here to write this. A few times over.
At one time the current went from my right hand through my chest to the left. Talk about the heart being involved. (And talk about being a dumb f*.) I was fine again after a few seconds.

Dangerous are the times when you grip around the conductor and the current makes your muscles cramp, so you cannot let go. But that's dangerous at 110 V as well.

Don't get me wrong, I'm not advocating sloppy workmanship around AC. I just hate people being afraid of things that they just need a healthy respect for.

[AndyKunz]

I work frequently in some high voltage areas, usually in our lab with very few safety precautions possible. I've been bitten by everything - AC, DC, 120, 240, 480V - and none of them was fun. The only reason I survived a 600VDC kick is because I was working overhead and as my body slumped down the weight pulled me away from the system. It took a few days before my arm, neck, back, and legs felt normal again. And that was with rubber soled shoes, one hand in a pocket, and working on an insulated pallet.

Another item to remember - DON'T WEAR JEWELRY (even wedding rings) AROUND ELECTRICITY!

Andy

[pilotpete2]

Hi Mark,
I was exaggerating a bit maybe ;)
The worst 120AC hit I've ever taken was many years ago when I was an apprentice tech for NCR Corp. I had just serviced the series wound brushed motor on one of those old classic chrome cash registers that you still occasionally see behind a "bar", when I put the motor back in and torqued down on the mounting screws, I had pinched the "hot" wire to the chassis and of course there was no ground wire connected :o , I was standing on the wet boards behind the bar and "hugged" the register to push it back in position, by the time I regained some level of awareness the bartender was ready to call for medical help, and I swear I had not been into the jack Daniels :p , it was waaay to early for that:o
Cheers,
Pete

Andy,
Very good point ;)

[Unterhausen]

the part of this I find strange is how hard states find it to execute people with electricity when they try, as opposed to how easy it is to electrocute yourself by accident. I guess we really don't understand everything there is to know about electrocution.

I have been known to wire 120vac circuits when they are live. A lot of times it makes things a lot easier. I don't think I would do it with 220, just don't like that much pain.

[Dan Baldwin]

Leaving one hand in your pocket sounds like good advice, but in practice, it doesn't really work. I need two hands to do just about anything I'm going to do; hold the wire in the lug with one hand, tighten the lug with the other.


Andy

How the devil did you get zapped if you only had one point of contact on a hot conductor? Where was the path for current to flow?

Dan

[AndyKunz]

At 600V, it doesn't take much - sweaty feet in rubber soles and an uncontrolled environment. The thing "looked" safe, but really wasn't due to a variety of hidden issues. While they may have jeopardized my life by being unsafe, the high impedance is probably what saved it.

Andy

[Skycruiser]

Here in New Zealand we're on 240V AC. The other day I was out in our pumphouse, stood in the doorway in bare feet on a metal door frame, reached in and pulled a plug out without flipping the switch first. The belt I got was strong enough to make my arm ache for ten minutes afterwards, and that was just leakage from the plug.

Best one I ever had though, was kneeling on a chest freezer to change a fuse (the old fuse wire kind) It was after dark and I had no light so couldn't turn the mains off. Someone had left a tail of fusewire sticking out of the block, and it just happened to be on the live side! Woke up five minutes later on the floor, fuse in hand, with a burnt thumb.

In response to the first question, neutral here is tied to ground so is perfectly safe. I always treat any wire as live until proved otherwise though.

[Gary Warner]

After getting shocked by the 35,000 volts from picture tubes, I now know why shock therapy is used with mental people. Though I don't understand it, I'm in a VERY bad mood after these shocks. The effects can last for days. Some people don't understand fully when I say "It'll change your attitude, that's for sure."

So far as what's safe (hot or ground) it's all in the hands of the electrician that wired the house... after a 3 beer lunch ;).

[pilotpete2]

Skycruiser,
I'm curious as to whether there is a slightly higher rate of electrocution in areas where you have 240Vac referenced to ground?
Here in the US and Canada the typical residential supply is single phase 240Vac with neutral/ground connected to a center tap on the transformer to provide split phase 120Vac or 240Vac using the full phase.
Pete

[Skycruiser]

Dunno Pete.

I do know that in NZ on average three people die each year testing 9V batteries on their tongue!

Actually even on 240V you get a good kick but as long as you don't clamp on to the wire there's a reasonably low risk of fatality.

Nick

[LOGICAL_PSYCHO]

Dunno Pete.

I do know that in NZ on average three people die each year testing 9V batteries on their tongue!
...snip

Nick

Can you cite one case of this happening?

[vintage1]

Skycruiser,
I'm curious as to whether there is a slightly higher rate of electrocution in areas where you have 240Vac referenced to ground?
Here in the US and Canada the typical residential supply is single phase 240Vac with neutral/ground connected to a center tap on the transformer to provide split phase 120Vac or 240Vac using the full phase.
Pete


Yes there is. Or would be if the regulations around mains equipment were not so stringent.

The average US or canadian house wiring would be rejected out of hand in the UK.

Typically we have RCDs on ether the whole house, or at least on sockets that are used outside, possibly on both.

EVERYTHING is wired 3 wire. So any chassis is at ground potential. Only equipment with double insulation is allowed to run without an earth wire.

Every house has a comprehensive switchboard, lights are separated from power sockets, so you can always isolate your freezer and leave the lights on..;)

There are stringent rules about bathroom wiring.

Actually more people are killed falling down stairs in the dark as they fumble for the reset on the safety switches, than are electrocuted. ;)

[AndyKunz]

Sounds like you guys are using the same code that is used here on new houses, vintage. My house is only 40 years old, but as I upgrade it, it's the standard I follow.

We have this concept of "grandfathering" whereby one is not allowed to change the law after the fact and then prosecute someone. In technical jargon it's called "ex post facto" and was one of the complaints our forefathers had against the crown 230+ years ago. Perhaps by now that concept has reached you guys as well.

You guys also have rules regarding the length of power cables, distance between outlets on the walls, etc. that solve non-existent problems.

And then there's the flicker of 50Hz...

Andy

[pilotpete2]

Vintage1,
As Andy said we actually have very similar standards here.
We built a new house 3 years ago when I retired.
Todays national code now requires arc fault breakers in all circuits that feed outlets in living areas in addition to GFI interrupters in all "wet" locations, these arc fault breakers will trip if there is any arcing detected, they are quite sensitive and will sometimes trip if you plug a device in with the switch on, I've had it happen.
The importance of ground fault interrupters is not understood by too many folks here. When they came in vogue I went and upgraded to them in our old home ( built in 1974), good investment though, as they were required to be installed before a C.O. (certificate of occupancy) can be issued to the buyer when ownership is transfered, at least in most jurisdictions.

Andy,
I believe it was non other then Nicola Tesla that determined that 60Hz was the minimum frequency required to not see the flicker.

Regards to All :)
Pete

[pilotpete2]

Dunno Pete.

I do know that in NZ on average three people die each year testing 9V batteries on their tongue!

Nick

Well, I would think that that would be about the same number, as the number of kids that get their tongue frozen to a flag pole at 20 below zero (C or F :D )
"I triple dog dare you!" :p
Pete

[Skycruiser]

Can you cite one case of this happening?

It must be true, I read it in a Readers Digest :D

Haha, busted! Here's another one for you: The elephant is the only animal with four knees.

[Skycruiser]

We're going through a slow renovation of a 100yr old house here, including the wiring. Thankfully the local sparkie is happy for me to do the work if he can check it. We don't have to have RCDs on all circuits here but with two preschoolers in the house I have anyway. As vint said, everything is earthed, even ceiling roses for light fittings.

[deh6]

When I was in the Navy (coming up on a 1/2 century ago!) I was told that 440ac was the most dangerous, i.e. most people killed. Higher than that, the voltage caused a muscle reaction that threw the person away from the wire. Lower than that the person had a chance of letting go of the wire...at least that is what they said.

In engineering school they said that about 60ma was required to kill a person, though I expect that it could vary widely with the path of the current, the physical condition of person.

[AndyKunz]

as they were required to be installed before a C.O. (certificate of occupancy) can be issued to the buyer when ownership is transfered, at least in most jurisdictions.

For non-commercial buildings, here they would be grandfathered. Commercial buildings come under an entirely different set of rules.

I believe it was non other then Nicola Tesla that determined that 60Hz was the minimum frequency required to not see the flicker.

But lots of folks DO see the flicker - I happen to be one of them (it is more common in near-sighted folks). It is especially annoying in the peripheral vision, where we are all more sensitive to changes than static.

What drives me nuts is being behind a car with LED tail lights. Every bump in the road, every slight movement of the head, and there's this string of red dots in my vision. I would HAPPILY pay the extra 25 cents that properly finishing the circuit would have cost.

But my wife does not have any problem with them - she doesn't have the slightest clue as to what I'm talking about.

Andy

[dleroi]

These stories take me back.

I used to sit on a wooden stool at my garage workbench and never gave a second thought about getting shocked while working on a piece of equipment. If I was working on something that was hot, I just kept my feet off the concrete floor and one hand out of the equipment. Well, one day my wife came out in her bare feet and poked a spoonful of whatever she was cooking into my mouth. We both got zapped. Then, I bought an isolation transformer.

[pilotpete2]

Hi Andy,
Actually the house I sold 3 years ago is in Ocean County, NJ :)
I wasn't aware of the difference with commercial property.
Where I live now there is no such thing as a CO, if you want to live in a half finished house, that's your business :p Too much big brother watching out for us :rolleyes:
Pete

[pilotpete2]

Don L,
Boy do I remember some of the things that actually passed UL approval in the past:rolleyes:
Back in the "good old days" it was common practice with tube radios and phonographs to have no isolation transformer, one side of the power cord was connected to the chassis, and polarized plugs where unheard of. Pull the knob off the volume control and touch the brass shaft while you were grounded and you stood a 50/50 chance of getting zapped :D
Just curious whether our friends in the UK or downunder can tell us if the same stuff went on there :confused:
Cheers,
Pete

[Brandano]

In Italy we use 220 volts, I believe the actual figure is closer to 230 to ensure compatibility with other european equipment. Every new or refitted hoe has to follow stringent rules with regard to the electric supply, with separate appliance and lighting circuits independently fitted with what here are called "lifesavers" breakers (I believe these are the RCD's you are referring in various posts) and overload breakers that will trip if the current exceeds the circuit's capacity. In this we're a bit different from England, where every plug is fitted with a fuse. 220 volts isn't significantly more dangerous than 100, they can both kill you. It really depends on how much current can get through, and maybe it's easier to fit lifesavers on a higher voltage. Referring to an earlier post, the neutral wire MUST be separate from the earth, or the lifesaver breaker won't be able to sense the dispersion of current to earth and trip in time. These work by checking that the current flowing through the phase wiring and the neutral wiring match. I think that one of the best security features for high voltage wiring is the German plug and socket design. The ground contacts are exposed, so that even if a child were to be able to get its fingers on it, he'd likely be grounded at the hand before being able to touch the live contact.

[Kevin Cox]

Interesting thread.

In the US, the lifesavers are called GFCIs. They are required in outdoor areas, kitchens, washer rooms, and bathrooms. I am curious as to what gauge wiring is used in the UK for 230v systems.

Existing homes (older) don't require GFCIs in these locations until the owner decides to sell it. It then will be required to have GFCIs in the above locations or even a new distribution panel to bring it up to 'code'. This however varies by location (county).

I would think most home electrocution occur in wet/damp conditions with maybe a few from playing DIY electrician.
We joke at work about which is worse to be "hit" by 125VAC or 130VDC. I have only felt the AC but they tell me DC feels worse. I will happily take their word for it. :D

[Markz]

I got "buzzed" on day fixing a live telephone line standing on a 12 foot ladder. Thing is, everything was fine - until the phone rang. 90vac @ 20hz is really annoying, it makes all your muscles shake at once! I almost fell straight to the floor
(Would that still count as death by electrocution?)

Marc

[Mike the Snake]

It's all about amperage.

I was told more fatalities occur from 120vAC because it's low enough to cause the person to freeze up. Really high voltage cause a jerk reaction (I got zapped by a TV, my injury resulted from my jerking back so hard (sprained finger, and hand went through an ornamental cactus!LOL)

220 volts is about the same danger since the volts are 2X but the amperage is less (I think).

The shock you get from the spark on a doorknob on dry days is like a million volts, but nothing behind it amperage-wise.

440 3 phase, Be Very scared! I'd also be scared of high DC voltage

[indtech]

Yep its not the 120 volts that kill you - its the fall when you react!

My elbow is scarred up from pulling back after getting bit.

[pilotpete2]

It's all about amperage.


220 volts is about the same danger since the volts are 2X but the amperage is less (I think).



All conditions equal, at 240, the current passing through you will be double that of 120 :eek: At least that's what George (Ohm) says :)
Pete

[MarkusN]

220 volts is about the same danger since the volts are 2X but the amperage is less (I think).
Slight misconception here. Amperage of the devices at 230 is lower (assuming equal power), but that doesn't change a thing, since the "device" in the case of electrocution are YOU. Which means you indeed get twice the amps that you would at 120.

But then, it doesn't really matter. 20 milliamps (!) can kill, if nobody is there to switch off the juice and you clamp onto the conductor. 50V will drive as much through the typical human body (that's why 48 V are considered safe). Under bad conditions (saltwater on your hands and bare feet, say) even 48 V can kill.