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Fortunate_K 12-23-2008 06:34 AM

Electical Safety
 
Hello,

Can anyone here please help me answer a question?

I have a room with 3 power points and each of those points has two plug in sockets. Sorry if I'm using the wrong terminology :)

The first one has a power supply for an antenna plugged into one of the outlets, and in the other is a power board that runs a large lcd tv, amp and dvd player which are all turned on.

The second point is empty.

The third one has a phone power cable in one outlet and in the other an extension cord running a laptop computer which is turned on.

I used to date an electrician once and he explained to me how the power points in a room are all run off one line from the main line or something like that.

So, if some one gets a shock from the power supply cable for the antenna, which is at the first power point, would they get a bigger shock (or bigger chance of a shock) because of the laptop on the extension cable at point 3 drawing lots of power? Would the chance of a shock be less had if the laptop were unplugged at the wall?

I really hope that makes sense. I'm in Australia so it's 240 volts

Many thanks,

Fortunate_K

KE2KB 12-23-2008 06:58 AM

Your chances of shock are only dependent on the voltage, and resistance. If you make contact with live parts of the circuit, how much current will flow through your body depends on the conditions of your skin (wet and/or sweaty means lower resistance, thus better chance for a severe shock), and the resistance of the connection itself.
It makes no difference whatsoever what is plugged into the various receptacles on the circuit, since the voltage will remain the same regardless.

AllanJ 12-23-2008 08:09 AM

The power points in a room are usually but not necessarily fed by the same circuit with the cable daisy chained from one to another.

Still, this makes no difference as far as getting a shock from improper handling or defective equipment.

The following probably never applies to areas with 240 volt household power but may apply to areas with 120 volt power. Sometimes outlets in the same room may be powered by different circuits connected to opposite sides of an electrical service that also provides 240 volts, at the breaker panel. A person could be subjected to a shock of 240 volts if he touches two pieces of equipment, both defective, plugged into different 120 volt power points (receptacles). Now 120 volts let alone 240 is usually lethal enough.

KE2KB 12-23-2008 08:50 AM

Quote:

A person could be subjected to a shock of 240 volts if he touches two pieces of equipment, both defective, plugged into different 120 volt power points (receptacles). Now 120 volts let alone 240 is usually lethal enough.
Now, that would require Murphy's law to happen<g>
A very unlikely, yet still possible circumstance.

Am I correct in saying that on a 240V only system, such as in Europe, the UK I think, and Australia, there is no grounded point, or is one side of the line still connected to earth?

InPhase277 12-23-2008 09:38 AM

Quote:

Originally Posted by KE2KB (Post 201707)
Now, that would require Murphy's law to happen<g>
A very unlikely, yet still possible circumstance.

Am I correct in saying that on a 240V only system, such as in Europe, the UK I think, and Australia, there is no grounded point, or is one side of the line still connected to earth?

Yes, there is still a grounded conductor, but it's a 2-wire system, not a 3-wire like our Edison system.

KE2KB 12-23-2008 12:41 PM

I would think that with a 220V system, there would be more electrocutions, but maybe due to a better plug/receptacle design that is not the case.
I had always assumed that their system was not grounded. Re-thinking that, it wouldn't make much sense, would it. No grounding = no lightning protection.

InPhase277 12-23-2008 12:53 PM

Quote:

Originally Posted by KE2KB (Post 201788)
I would think that with a 220V system, there would be more electrocutions, but maybe due to a better plug/receptacle design that is not the case.
I had always assumed that their system was not grounded. Re-thinking that, it wouldn't make much sense, would it. No grounding = no lightning protection.

The voltage really has no bearing on electrocutions. In the United States, more electrocutions occur at 120 V.

Yoyizit 12-23-2008 02:08 PM

Quote:

Originally Posted by InPhase277 (Post 201796)
The voltage really has no bearing on electrocutions. In the United States, more electrocutions occur at 120 V.

Yes, the symbol for current, I, is for the French word intensité.

1 mA is perceptible
10 mA is painful,
20 mA you can't let go
100 mA is possibly fatal,
4 to 8 amps is delivered by an electric chair (at 2400 vac).

But exposure time is also important. 20 mA for 1 second is permissible, as is 100 mA for 1/10th second, according to the GFI trip curve.

Only one person in the Navy was electrocuted by 47v.
Sewer worker use 28v lamps.

More than 600v punctures the skin so you lose the considerable benefit of skin resistance (I still have the scar).

Current passing through your head or chest is much worse than current passing through extremities, although nerve damage is still possible.

400vdc, from a Heathkit TV degaussing coil, from finger to shoulder, will leave you wondering about changing your career.

1300 people/year in the U.S. get electrocuted, the majority of which were not working in the field. In the scheme of things, this is "down in the noise."

KE2KB 12-23-2008 04:18 PM

Quote:

1300 people/year in the U.S. get electrocuted, the majority of which were not working in the field. In the scheme of things, this is "down in the noise."
Compared to the number of people killed in their automobiles, it sure is!

I would think that more people in the U.S. are electrocuted by 120V because more people use 120V than 220V. We don't have many appliances which we have ready access to running on 220V.


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