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Evil, Wicked, Mean, Nasty
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Discussion Starter · #1 ·
How much voltage/amps is too much to leave exposed?

It's quite common to attach a 9v battery to an led as a throwie. Quite obviously...this must be safe. I've never heard a throwie killing someone.

So...a buddy of mine at work and I got into a conversation about how much voltage is okay to leave exposed. Say for example, my prop uses a 12 volt 1000mA adapter. And I build banana plugs to it to connect a prop. At what point am I endangering someone if they were to touch the plugs?

I'm not looking for links to sites. More or less...comments on the normal type power adapters commonly used for props.
 

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Good question Darklore? My friend is a licensed electrician. He told me something about water, moisture, any way it can grab you like 110. I just avoid running any thing out that can be touched or stepped on. That said I know the 110 drop cords I use get moisture when it rains.
 

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It's not the voltage.It's the current that's dangerous.220V is less likely to kill someone than 110Volts.It goes back to ohms law.Voltage = Current X resistance.The lower the voltage,the higher the current,relatively speaking.3 phase power is a different story all together.
It's actually easier to break away from 220 volts than it is from 110 volts,because the current is lower.
Think of a car battery.Only 12 volts,but LOTS of current(cranking amps).You don't want to touch your tongue to both car battery terminals.
 

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Stays Zesty in milk
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If you want NEC code definitions (& the confusions & faults) I can give them, but they don't really help you..."Low Volt" has definitions ranging from 0- 250 volts, depending on the application & code section! I am still new to the "prop" aspect of electricity & electronics, but not the "real world" version. I would insure that nothing "live" be exposed in any way, shape, or form, regardless of voltage. Just a few milliamps can kill.
 

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Even 12V at 1A has the potential to stop someone's heart, although the conditions would have to be just right (someone with a bad heart standing in the rain touching the conductors in a way that lets the current travels through their heart - not likely). I'd imagine you'd be fine, especially if you use audio type dual banana plugs that are centered 3/4 inches apart. Not much chance of giving anyone much more than a "tingle" at those power levels.

It's not the voltage.It's the current that's dangerous.220V is less likely to kill someone than 110Volts.It goes back to ohms law.Voltage = Current X resistance.The lower the voltage,the higher the current,relatively speaking.3 phase power is a different story all together.
It's actually easier to break away from 220 volts than it is from 110 volts,because the current is lower.
Think of a car battery.Only 12 volts,but LOTS of current(cranking amps).You don't want to touch your tongue to both car battery terminals.
You've got the formula right, but your math is a little off. The resistance to electrical current of the human body is relatively constant, so to increase the voltage you have to increase the amperage. Let's say a body has 2 ohms resistance - 55 amps X 2 ohms = 110 volts, and 110 amps X 2 ohms = 220 volts. You'd actually be calculating amps in this case (110V / 2 ohms = 55A) since both source voltage and resistance are fixed.
 

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Evil, Wicked, Mean, Nasty
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Discussion Starter · #8 ·
All good comments. But let me clarify.

I'm only referring to standard wall warts. I'm aware that its amps that can kill. But my buddy and I were discussing something closer to what hedg12 stated. A 12vdc adapter at 1A can kill...but what's the likelyhood? In essence..if I expose 12vdc at say 1A to 1.5A...and someone touches it. It was my guess that although possible...it's highly unlikely it would harm someone...even a child.

When we looked it up on the net...we find that indeed the number of amps, or even mA, required appeared to be extremely weak. Yet the references still say it can be lethal.

So my question...is it more like the statement of a drowning in an inch of water. It can happen, but highly unlikely. Or is it more like...damn that's going to hurt, and probably do away with the cat?
 

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At the power levels you're talking about it might scare the cat, but not do away with it (so if that's your goal, up the voltage!) I don't like the idea of leaving any power wires uninsulated/exposed, but it's not likely that you'll hurt anyone. I have a bench power supply made from an old PC power supply that I use banana plugs on & I don't think I've ever been hurt by them (& I'm clumsy...)
 

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Non technical approach

Interesting question…. From a practical standpoint I think any wallwart with a barrel connector is going to be safe.

Why… because if it wasn't the manufacturer would be sued out of existence. Think of all those thousands of wallwarts plugged into the wall but not plugged into the electronic device with cords lying on the floor. There have to have been hundreds or thousands of dogs, babies and cats have put the ends in their mouths. I've never heard of any fatalities. (I did a quick Google search and all I came up with was an urban legend about a Nigerian man and his cell phone charger.)

BUT… I thought about it a bit more and realized that the key reason that wallwarts with barrel connector are safe is the design of the barrel connector. By design, if the connector is shorted out the current can't travel through the heart. The current can only flow a very short distance. Say for example, from the positive inner connector through your tongue and to the outside of the connector.

So… It's using the banana clips that ups the danger level. Now it is possible but not likely that you could handle the clips in such a way as to cause current to flow through the body.

Probably the cheapest and safest thing to do is to buy a female barrel connector jack and use that on the prop.
 

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Lots of good replies so far. I, too, would have to say a wall wart is probably going to be pretty safe. I've heard the old adage "it's not the volts that get ya, it's the amps". But there is more to the story than that even. People use arc welders all the time - which can run hundreds of amps, and you don't see them dropping dead all the time. You can touch the leads of a car battery which can put out several hundred amps and nothing happens. So clearly there are many variables.

I also don't know that I would agree 220V is less likely to kill someone than 110V - Specifically because the V=IR law. Given the resistance (R) of your body is constant, doubling the voltage (V) will double the current (I) traveling through you. So you would think 220V has double the chance to kill someone as 110.

As anecdotal evidence, I used to work with some old guys who claimed 220 was the most dangerous voltage. Their reasoning...110V and lower was nothing to worry with, 440 and higher would blow you right out of the way. 220 would grab you and suck you in. :)

Though on the flip side, I have been 'shocked' by a car battery as well. I reached through the metal dash of an old car to grab a wire (which was hot with 12V at the time) The combination of the wire on my fingertips and the metal against my arm and I got enough enough of a jolt to make me jerk and let go.

There is also 'safe' from the 'it probably won't kill you' standpoint and 'safe' from the 'legal defense' standpoint. If someone is in a haunt and happens to get 'shocked' by even bare 12V wires, suddenly they might have more of an injury than they think and it would be an up-hill battle on the legal defense side.

Me personally, I try to cover all exposed wires to avoid accidental (an or mischievous) shorting. But looking around the house it seems that 12-24 volt adapters are laying about without much protection on the ends. Much above that and you start seeing some protection and/or warnings to turn off the power when working on the circuit.
 

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220V/240V IS more dangerous than 110V which is why in the UK, tradespeople have to use stepdown transformers and 110V power tools.

110V gves you a much better chance of surviving as it is a lot less likely to stop the heart or cause arrhythmia.

400V will not necessarily 'throw you out of the way' - what happens is that when you act as a conduit by touching a live item, all your muscles contract - this means that if you have grabbed something, your hand actually locks round the item - when doing my electronics course as a youngster, we were taught never to make grip contact with anything but to flick the back of the fingers over it and that way, if it was live, your muscles contracting would actually pull your hand away. Our tutor used to play practical jokes on us by wiring things up to shock us - 3 months of this and the habit of never gripping anything is permanent!

With the higher voltage, the muscle contraction is more violent so the muscle spasm may be able to break the hands grip on the item.

The accuracy of this is the higher the voltage, the more likely it is to kill you providing there is some current behind it. 110V is more safe than 220V but I still wouldn't have mats etc linked to 110V directly.
 

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Your simple question does not have a simple answer. In a more laboratory-esq setting, I can give you a very safe, reasonable answer. In the real world application aspect, too many variables can change in the environment for a true "safe" answer. At least one that I am comfortable with giving out to just anyone... There is also the mater of liability to consider.

You may keep a 5 gallon bucket, 1/2 full of water, locked away in your backyard. Not particularly dangerous.

Put that same bucket in the middle of a daycare filled with toddlers. Potential murder or child endangerment charges.

Electricity is not water.

As far as dangerous, electricity can do more than cause fatal cardiac arrest. It can burn & cause fires. It can cause nerve damage. It can arc flash & explode. It can cause secondary injuries, a minor shock can cause slip & fall. A battery is filled with acid. It can leak & cause chemical burns. It can get hot & explode.
It can also do absolutely nothing.

But as to a 12v wallwart, it is still connected to a 120v, 15-20a circuit. Unmodified from the factory, should it fail in a "bad" way, the manufacturer would be liable. If you have modified the wallwart in any way, you are now responsible, even if the fault lies within the wallwart.

I'm sure you know all this already, but some may not.

As an electrician, I cannot give you a "this is just fine" to leave exposed, kind of answer. I cannot advise you in using the banana plugs or any other, if they are not UL listed for that purpose. I can tell you a bit about accessibility & exposed live parts, & the simple answer is don't leave any connection bare or exposed or in reach of the public, at any voltage. They do make insulated banana plugs, but I don't know if they are UL listed or rated for your purpose.

I know a lot of what you do is safe, both in theory & application. But if there is a chance for injury or it is not to code, I cannot publicly or officially advise you to go for it.

As for what is a truly safe voltage? My answer would be 0v that are accessible. Why take the chance?

Charles Dalziel did some work on this on human guinea pigs! I know that you wanted no links, but this one may help, or just help to confuse.
http://www.highvoltageconnection.com/articles/ElectricShockQuestions.htm
I also am not the final authority, or claim to be, on this subject. Do what you will, at your own risk.
Don't let me keep you from building cool props, either! Just be safe & safety first!
 

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As people have said, it's not a simple answer.

As you're only using wall adapters, things shouldn't be too bad.
BUT.. that's said as long as you're taking relevant precautions.

I wouldn't use the connectors you're considering, I'd go for something that fully covers the connections, has some form of cable clamp (to prevent cable pulling out) and probably offering some polarity protection, so they can only be connected one way (many wall adapters are DC, so polarity is typically important)

One thing that's not been said is ensuring the connections are good and tight.
One of the worst problems I've seen many times is caused by loose connections, this may cause arcing, easily at 1amp, which in turn causes heat, this leads to wires overheating and insulation melting, connector melting and possible fire risk.. just make sure they're tight or even better soldered where possible.

Also make sure you use fuses where appropriate, of the correct type and values..

Perhaps stick to the standard DC connectors, the little tubular ones, you can get in-line plugs and sockets, easily make extension leads and panel versions of the socket just need a hole drilling to fit (I think you can get locking ones too)

Si
 
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