240v AC that will not give shock !?

[aljamri]

Hi everybody:

Is it possible to get 240v AC that will not cause electric shock?

The served load is not more that 100 mA.

Thanks

 

[crutschow]

If you generate it with a frequency above 40kHz or so, similar to a Tesla coil, you won't feel any shock.

 

[aljamri]

but I need to use 240v Ac at 50 Hz load.

 

[Nigel Goodwin]

but I need to use 240v Ac at 50 Hz load.

It always has the potential to give you a shock, if you want to minimise the chance, then use an isolation transformer, that removes the most common shock hazard.

However, you would be better off telling us EXACTLY what you're trying to do, rather than vague questions.

 

[Hero999]

Silly question, 240VAC 50Hz will always shock you.

Make sure you use adequate insulation and design to the reliant standards and your project won't shock you.

If you generate it with a frequency above 40kHz or so, similar to a Tesla coil, you won't feel any shock.

It will still burn you.

 

[Reloadron]

but I need to use 240v Ac at 50 Hz load.

Which is adequate enough to not just give you a shock but cause death (a shocking experience). That can really ruin a day. You can minimize the shock hazard in several ways, Nigel pointed one out. The bottom line is 240 VAC @ 50 Hz. is capable of killing you. Whenever working with mains voltage use caution.

Ron

 

[Hero999]

What are you powering?

Why not reduce the voltage to a less lethal level?

 

[aljamri]

Silly question,

It would be better if you have not started your answer with SILLY, since it serves no purpose. The question that you feel less than your level, may attract somebody's else attention. You'd have simply just ignore it and make your self and everybody comfortable.

English is not my first language thus searched in my dictionary for this word and found three meanings, all of them are negative and the worse one is what's applicable here.

Fortunately this was not my first thread in this fine forum, otherwise it would be my last if I read such answer.

For all noobies who read this as their first thing in this fine forum, do not worry, this is not the way you will be answered. I've spent FOUR years here, getting very good answers that contributed in building my electronics information in many ways.

 

[unclejed613]

sorry, but 20mA at ANY voltage can kill you. higher voltage just makes getting to 20mA more likely. first of all, get in the habit of keeping one hand in your pocket when working with any electronics whether it's powered up or not. make sure to unplug a device and discharge capacitors before disassembling anything. if you repair electronics as a living, getting zapped is an occupational hazard, and after 40 years of doing this i still get bit occasionally, usually when i'm in a hurry and forget to unplug something or discharge a power supply cap. also, don't wear any jewlery, rings, watches, etc while working on electronics. where i work, somebody died because they didn't discharge the power supply cap in a microwave oven.

50 and 60hz power is especially dangerous because it can travel through the core of your body easily. above 30khz or so, current tends to travel along the surface of the body, but it can still but burn you badly, DC is actually more dangerous, because it locks your muscles and you can't pull your hand away (this was a big part of the DC vs AC debate between Edison and Tesla/Westinghouse back in the late 19th century). AC kind of forces you to pull back when you get shocked. i've seen a demonstration where somebody standing on top of a 60khz tesla coil set a piece of wood on fire that they were holding in their hand. of course, they wrapped the bottom of the wood in metal foil so that the current density on their skin was not high enough to burn them.

 

[aljamri]

However, you would be better off telling us EXACTLY what you're trying to do, rather than vague questions.

Sorry Nigel, I've forgot your old advice the elaborate in describing the case to get the best answers.

This is for an application that my friend asked my if it is possible. He is in Power Meter shop, and having many deflective meters, sometimes they need to service them live and uncovered.

I've told him from my humble experience, 240v AC causes shock whatever you played with the other parameters, but to make sure I've placed this question, and if you've noticed, I've ended it with EXCLAMATION mark.

 

[aljamri]

Thanks Uncle Jed for your valuable, parental, practical, advices.

get in the habit of keeping one hand in your pocket when working with any electronics whether it's powered up or not

This remind me with one of our instructor who we always noticed that he repair T.V. set with one hand in his lab coat, every body noticed this but no body asked him for the reason until one day, I've encouraged with the information I've gathered from my 101 about TV. to open the back cover for our junk TV while it is ON, trying to put my tester screw ( the only test instrument I know at that time ), In fraction of a second I found myself flying toward the wall with bang both my self and my screw. Since then, I'm trying to repair any electrical/electronic equipment, except for TV.

 

[bychon]

Home grown wisdom: There's no such thing as an old, stupid electrician.

Another way to put it: If you keep accepting situations where there is a chance you'll get killed, the odds will eventually come around.

 

[Nigel Goodwin]

This is for an application that my friend asked my if it is possible. He is in Power Meter shop, and having many deflective meters, sometimes they need to service them live and uncovered.

Then either feed it via an isolation transformer, or work in a totally earth free environment.

These both do the same thing, effectively preventing you getting a shock from live to earth (one by removing the live, the other by removing the earth). You can. of course, still get exactly the same shock between the two wires.

 

[Hero999]

It would be better if you have not started your answer with SILLY, since it serves no purpose. The question that you feel less than your level, may attract somebody's else attention. You'd have simply just ignore it and make your self and everybody comfortable.

English is not my first language thus searched in my dictionary for this word and found three meanings, all of them are negative and the worse one is what's applicable here.

Fortunately this was not my first thread in this fine forum, otherwise it would be my last if I read such answer.

For all noobies who read this as their first thing in this fine forum, do not worry, this is not the way you will be answered. I've spent FOUR years here, getting very good answers that contributed in building my electronics information in many ways.

Sorry if I offended you, may be I misunderstood what you were asking.

Of course 240VAC 50Hz will shock you.

Didn't you mean to ask about building a project power from 240VAC mains that doesn't pose a n electric shock hazard?

If so that's a very broad question and certainly isn't silly.

It depends on what the project is.

There are books written on the subject.

I have some experience of designing mains projects and following relevant safety standards.

What project do you want to build?

 

[aljamri]

or work in a totally earth free environment.
(one by removing the live, the other by removing the earth).

Ohhh my god, Is that safe ?! I've seen once an old electrician removing the main earth conductor from the old ELCB before doing some electrical connections, and returned it after finishing his work. I still remember that I thought " what the hill this old man is doing " . Unfortunately, I don't know his place, otherwise I owe him apology.

may be I misunderstood what you were asking.

Of course 240VAC 50Hz will shock you.

Do not worry Hero999, this is one more reason Nigel can add to his advice of elaborating the problem " to get better answers ", and " to avoid any misunderstanding".

As ETO colleagues, I appreciate your continuous help for me and for everybody here and your 14.8 k post is clear evidence even though we both joint ETO the same year, with two month difference.

 

[Nigel Goodwin]

Ohhh my god, Is that safe ?! I've seen once an old electrician removing the main earth conductor from the old ELCB before doing some electrical connections, and returned it after finishing his work. I still remember that I thought " what the hill this old man is doing " . Unfortunately, I don't know his place, otherwise I owe him apology.

To get a shock, or light a bulb (or anything else) you need a complete circuit.

You get a shock off a live wire because the neutral is connected to ground at the sub-station - so the shock goes from live, through your body, down to ground, and back via the ground to neutral - a complete circuit.

To prevent this you just need to break the circuit at ANY POINT - it wouldn't be wise to disconnect neutral from earth at the sub-station, so you have the choice of fitting an isolation transformer, which removes any connection between the supply and earth - or making it impossible to get a shock to earth, by having an earth free environment. As a service engineer I do BOTH, all benches are fitted with isolation transformers, and the workshop itself is an earth free environment as well.

There's nothing intriniscally safe about earthing, it helps under certain limited circumstances, but is MORE dangerous under just as many circumstances - basically you need to know exactly what you're doing, and why - but a lot of people, including many on here, don't seem to understand that.

 

[crutschow]

It will still burn you.

True, but that is unlikely to kill you. And he was asking about shock and that was my somewhat facetious answer to his question.

 

[aljamri]

There's nothing intrinsically safe about earthing, it helps under certain limited circumstances, but is MORE dangerous under just as many circumstances - basically you need to know exactly what you're doing, and why - but a lot of people, including many on here, don't seem to understand that.

Ohhh my God, after all these years of playing with electricity, with a rate of 2 to 3 shocks per year, I found that earthing is of no benefit. That's a stunned fact to know in my age. Earthing used to be essential part of our Electricity believe, a standard that we have to memorize and apply with no further discussion.

I remember during my study, I've been told to connect any socket in the W.C.C. through an isolation transformer, just like this, without any discussion to the theory behind it.

One old proverb said " gaining knowledge is like digging a hole in ground, as you remove more, the hole gets larger and larger"

 

[Hero999]

So you might ask why is th e mains earthed?

The mains is earthed because it ensures the maximum voltage with respect to earth is 230V. If it wasn't earthed, it could float at any voltage, suppose someone connected a 10kV autotransformer so the mains and connected the high voltage secondary to earth, the mains would then float at 10kV, causing insulation breakdown, electric shocks and fire.

Earthing is only important when the device is (class 1) and is connected directly to the mains. If you use an isolation transformer, the device doesn't need to be earthed but, if you have many devices running off the same transformer, you should connect their earth connections togerther because it ensures their metal cases are all at the same voltage.

 

[aljamri]

So you might ask why is the mains earthed?

YES, thats consequently the next question!

Nigle, Hero, Thanks, but thats too much for me to change believes in one week.