trans atlantic electrical differences

[tbellemare]

But it's not the current OR the voltage that kills, it's a combination of both. They are always connected to each other.

Well put, Alex.

Tom

 

[Ken Nagrod]

Voltage is stored energy.  It's when it's released (current) that the potential for shock/electrocution can occur.  In theory, voltage can't hurt you.  Alternating current varies, in its simplest terms it goes from zero potential to positive, back to zero, then to negative, back to zero, repeating itself.  Because of the cross to a zero potential, anything living coming in contact with it is afforded the time to separate from the source whereas with direct current, you don't since there is no "off" time or zero potential.  That's why DC current is more dangerous than AC current.  Now just to clarify, if you're being electrocuted by a high AC current, your muscles are going through such spasms that you may not be able to physically free yourself and your nerves and organs are being fried as well, so the brain may not be able to think, "I need to separate myself from the current source before I resemble my wife's pot roast from last night".

The human body's resistance varies with many factors and among everyone.  There is no "about" or a range.

 

[jonny round boy]

I wasn't saying that getting an unlimited shock from 220V was less harmful than a shock from 110V - as has been pointed out, with the fixed resistance of your body (at a single point in time) without any form of protection 220V will drive twice the current as 110V.

My point is that you're far more likely to survive a shock from 220V with an RCD fitted to the supply than you are from 110V, which doesn't have any protection other than a standard breaker or fuse.

At the moment, a lot of sites in the UK will not allow you to use the former, but will force you to use the latter.

 

[Rob Z]

If I remember correctly, it takes less than a 1/4 amp to kill a human. The smallest breaker that is common is 15 amps.

It actually can be as low as 30 to 60 milli amps. Fuses that are rated at 15 amps are meant to prevent a short circuit (which can start fires), not an electrocution. To prevent an electrocution you need a RCD or GFCI as it's named in North America. A fuse detects an amp overload, that's why it's rated at a certain threshold. An RCD detects a difference in the current that's send and the current that returns. When you get electrocuted, the return value is different from the sent value because of leakage to the ground (through you).

But it's not the current OR the voltage that kills, it's a combination of both. They are always connected to each other.  

Good explanation, Alex.  I'll confirm with my sparky, but I think the GFCI's here  are set to "trip" with an imbalance of only 5 milliamps, which is an order of magnitude below the lower threshold for a potentially deadly interaction.

 

[d8b]

Good explanation, Alex.  I'll confirm with my sparky, but I think the GFCI's here  are set to "trip" with an imbalance of only 5 milliamps, which is an order of magnitude below the lower threshold for a potentially deadly interaction.

In a typical Belgium house you find a GFCI of 300mA just after the main breaker and a 30mA one for the wet zones (bathroom, kitchen,...)
During my job safety training I was told that 200mA trough the hart could be lethal. So the typical 300mA GFCI doesn't really make sense, but that's what's required by law here.

greetz,

Philippe

 

[AlexThePalex]

During my job safety training I was told that 200mA trough the hart could be lethal. So the typical 300mA GFCI doesn't really make sense, but that's what's required by law here.

It is not the amount of current alone that is important, the exposure time is also important. If the time is short enough you can survive larger currents. That's why the most important factor is that a GFCI can react in milliseconds and not necessarilly if it's 30 mA or 300 mA. When you get zapped the chance is very high the current will become bigger than 300 mA so the 300 mA GFCI will trigger. And it's also highly probable that that 300 mA won't all go over your heart. Nevertheless, the lower the number the better so in that light 300 mA seems a bit high indeed. In Holland all GFCI's must be 30 mA now.

But there are so many factors involved. Governments can only set general guide lines to minimise the risk as much as possible. The vast amount of incidents where people get zapped end without any harm done, and in some cases people die for the craziest of reasons.

 

[semenza]

Personally I don't care how "safe" a certain current, voltage, amperage is or how little it takes to kill me. I just make sure I don't get zapped. The worst (only ) thing I have been zapped by is an electric fence designed to keep livestock where they belong.  What ever power it has  is not enough to kill humans, but it hurts enough that I don't want to do it again  [eek]

Seth

 

[Rob Z]

I called my sparky to confirm-GFCI's for residential applications  are set to trip for a 5 milliamp imbalance.

He told me for certain machinery applications, GFCI's are available which have different settings.

 

[Alan m]

i know it is easy to say i wont get shocked but the problem is beung zapped in usually an accident. it is very easy to cut into a wire with a recipricationg saw when opening a wall (i know the breaker should be off but there could be line going somewhere else) drive a nail or screw into a stud and miss slightly hitting a wire. even with the best of intentions and skills you can never account for the person who went before you and ran the wires, you dont know where they ran anything or code violations they allowed. 
its like saying i wont wear my seatbelt because i wont crash.

i was running a welding socket at home from one shed to another (was an extension cable but not permanently insated but still pluged in in the first shed) i needed to cut it to length . i had been useing it that morning and was sick of tripping ove the excess so decided to shorten it. i sent some one up to plug it out so i could work on it . they should have known what they were doing but didnt plug that one out but said they did so i cut. i blew a big chunk out of my brand new pair of insulated (thankfully) electriians pliers and tripped the breaker. gave me some fright . you can never be too carfull around electricity it only takes one little bit of confussion and the line isnt off