Touching appliance plug prongs to live wires

Factual Questions
21

Find someone who is qualified to do this and also make sure that this person thinks that touching wires to the prongs of an appliance to test something is a really bad idea.

One thing that’s striking about this thread is the plethora of vague hints of Bad Things to Happen if one tried this, contrasted with a complete lack of any specific detail as to exactly what that is and how it might come about.

I mention this so that in the unlikely event that there is someone who has something substantive to add on this subject they can provide some actual information instead of uninformative condescension.

But speaking of decades of electrical engineering reminded me that there’s a guy down the block from me who is a retired professor of electrical engineering, so I asked him this morning. He pointed out that you could get a shock, and mentioned that there are other tools, and I said OK but if you did it this way what could happen, and he said you could get a shock and he doesn’t like getting shocks. Seemed to sum it up.

[I actually have an uncle who has been a licensed electrician with his own firm for about 50 years or so I would have put the question to him or one of his sons who also work in the field but he and they can be very hard to get hold of and the question seemed straightforward. Still does, even if the answers haven’t been.]

22

Have you ever been shocked by 120 vac? It really, really hurts and can continue to ache for hours. It can also leave you temporarily dazed. You’d do anything to stop the shock like jumping off a ladder. It can kill you. A circuit breaker can fail and the house burns down.

23

Oh, come on now! Don’t be ridiculous.

24

I once asked an electrician I know if he’d ever been shocked. He replied, “this week? No, but it’s just Monday”.

I asked my gf’s dad the same question. He looked at me, wondering if I was joking. He then replied, “No”. He worked mostly with very high voltages in a steel mill. He also worked residential for his early career.

25

Trying to move possibly live wires so that they touch the prongs of an appliance is a significantly greater shock hazard than just sticking meter probes onto wires.

Connecting an appliance only measures a voltage differential between the two wires. If both wires are live, the appliance won’t turn on and you might think the wires are dead and disconnected, when in fact they are both live and both present a shock hazard if touched.

Similarly, if you think that both wires are dead and disconnected and they aren’t, or if you misunderstand how the wires are connected, any wiring changes built off of those assumptions could result in a short circuit and potential fire (in addition to the potential shock hazard).

With a shock hazard, on the low end you’re talking about probably some swearing and that’s about it. On the high end you’re talking things like cardiac fibrillation and death. With a short, on the low end you’re talking a popped breaker. On the high end, the house burns down and people die.

Is that specific enough?

26

I’m an electrical engineer, so I spend more time designing things on a computer than touching things with my hands. While I’m not touching wires every single day like an electrician, I do have a fair amount of hands-on time with electrical wiring.

Admittedly, I’m probably a bit too lacking in caution when it comes to climbing around in cabinets with 120 or 240 volts. I don’t start getting cautious until the voltages get to 480 and above.

That said, I have only been shocked twice in my life. The first time I was about 6 years old and I plugged a record player into the wall socket while touching both prongs of the plug with my hand.

The second time was around 2001 or so. I reached into a prototype for a piece of equipment and got shocked. I should also point out that I was the lead designer of this equipment, and I should have known better.

27

Is that specific enough?

Yes, thank you.

I should note that much of what you write doesn’t apply to what we’re trying to do, as described in the OP and a subsequent post. The only thing we would do based off an assumption that “the wires are dead and disconnected” is that we would cap them back up and close up the junction box and run new wires from a different fixture. It’s only if the appliance works that it’s relevant, since if the appliance works then a light fixture could work too.

In sum, you need to avoid touching the bare wires, as mentioned in the OP. Or touching them to each other, I assume. OK.

28

This is what clip leads are for…

29

I once asked an electrician I know if he’d ever been shocked. He replied, “this week? No, but it’s just Monday”.

FWIW, my brother told me that our aforementioned electrician uncle routinely works on live wires and shrugs off an occasional shock. But I suspect that’s a “familiarity breeds contempt” mindset, commonly found in people who are routinely exposed to any particular type of danger.

As I understand it, the danger of 120 volt exposure has a lot to do with how long you’re in contact with it, as well as what you do in reaction (e.g. fall off a ladder etc.)

30

This is what clip leads are for…

Yeah, notwithstanding all the above, I think maybe I’ll bring along my multimeter …

31

Here are some specific things that can go wrong.

You open up the junction box and find a bunch of wires connected with wire nuts. You unscrew a wire nut to attach an appliance, and the springiness of the wires cause them to touch the grounded junction box. Best case, you find out which breaker those wires are on. Maybe a spark shoots off before the breaker trips and it lands in your eye (this is on the ceiling, right?). Maybe the spark just lands on your face or arm. Maybe the breaker is defective, and a fire starts.

You successfully remove a wire nut and attach an alligator clip wire to the exposed end, but does somebody who doesn’t own a multi meter own alligator clip wires? Now you have a potentially live wire dangling down. Do it again. Attach the ends of both wires to the appliance. Oops, these are 240 volt wires that run to the dryer, and the smoke escapes from the appliance.

You don’t own alligator clip wires, so you try to stick the bare wires into the little holes in the plug blades of the appliance. Now do it again with another wire into the other plug blade. Oops, they touch. Best case, you find the breaker.

These wires were installed by an incompetent homeowner, and the colors don’t correspond to their use. The box itself isn’t grounded, but hot. The neutral and hot are reversed. You manage to get the power checked and turned off, but forget which wires go together, so you end up creating a short, and discover when you turn on the breaker. You don’t properly get the wires spliced back together, leading to arcing in a closed junction box.

I can go on and on, and I don’t do this for a living, but I am good at thinking up disaster scenarios.

32

Bear in mind that a multimeter, even when set to read voltage at a sufficiently high enough range, may be perceived as a short by GFCI or RCD breakers.

33

Seems unlikely, unless you are using some VOM from the stone age. Any modern DVM will have a minimum of 10MΩ input impedance, which equals 12µA of current at 120v - far below the 5mA trip threshold of a GFCI.

34

Bitter experience. Digital multimeter, brand new.

35

I would guess people have not wanted to be terribly specific lest you use that specific information to go forward with your Very Bad Idea, since it is fairly obvious that you are going to dismiss the “don’t do it” part of the advice. If you have relatives who are electricians, I think you should definitely contact them for advice, if you will take it.

People die from shocks from residential wiring. The most basic rule of safety is to not handle live wires. And, you’ve been told that your idea could give you false information. What more do you want from this thread?

Here’s lots of detail about what could go wrong. Electrical Injuries - StatPearls - NCBI Bookshelf

Spoilers: household current can kill or severely injure you. Holding something in each hand is a great way to get the current to go through your heart. As little as 15mA can cause muscle tetany that a grown man can’t overcome – you won’t be able to let go of the wires.

36

Electricity generally kills you in one of two ways.

At low current levels, electricity can interfere with the heart’s rhythm. Your heart has a bit of a funny design in the way its pacing system works, and if you get its rhythm screwed up, the heart just kinda sits there and shakes chaotically. This is called fibrillation, and since the heart isn’t really pumping blood at this point, you pass out fairly quickly and die a short time later due to the lack of blood flow (and lack of oxygen) to your brain.

The funny thing about the heart’s design is that this fibrillation state is stable, meaning that if you get it into this state, the heart will happily stay in fibrillation forever (or at least until you die). Better hope that someone is standing next to you with a portable defibrillator. Otherwise there’s a good chance you’re toast. And even with a defibrillator, nothing is guaranteed.

It takes a surprisingly small amount of current to throw the heart into fibrillation. Most safety standards are built around 5 mA as being the “safe” amount of current that can pass through the heart, though obviously there is a bit of guesswork involved here and we haven’t exactly done a huge amount of human testing to verify this number. As the current increases above 5 mA, the chance of fibrillation and death increases, and once you get around 100 mA the chances of stopping the heart are pretty good.

To put it in perspective, most household circuits will trip the breaker at either 15 or 20 amps, which is 15,000 and 20,000 mA respectively.

The thing about this type of death though is that it is very hit and miss. The heart is significantly more susceptible to getting thrown out of rhythm at certain phases of its heartbeat than others, so there is a huge amount of randomness here. Most people who get shocked by 120 volts don’t die, but the chance of death is there. The current also has to go through your chest cavity, which is easily possible if you are standing on a ladder and trying to touch an appliance cord to wires inside an overhead junction box. All it takes is one hand to touch any of the live bits and the other hand to touch the outside of the junction box.

If you are a stupid kid like I was and grab both prongs of the plug when you plug something in, the path of the current is from your finger to your thumb and doesn’t go through your chest.

Just keep in mind that anything metal that touches the ground (water pipes, aluminum siding, sink faucets, etc) is basically grabbing onto the neutral and ground connections, electrically speaking. It’s very easy to accidentally create a circuit where the path of the current goes through you and through your chest.

As the current level continues to rise, the chance of death surprisingly starts to decrease. This is because if you get enough current going through the heart, instead of going into fibrillation, the heart muscles all just clamp. This is still bad, since the heart isn’t pumping blood, so if no one is around to remove the source of the current, you’re toast. But once the source of current is removed, under these circumstances the heart usually just starts beating again. At 120 volts you usually don’t get enough current for this type of thing, but depending on circumstances it can happen.

Increase the current further though and you get into the second way that electricity kills you. It literally cooks you to death. Current flowing through anything other than a superconductor will make heat. If you put a nail in either end of a hot dog and connect the two wires of an electrical cord to those nails (one to each nail), and then plug the cord in, you’ll cook the hot dog in a surprisingly short amount of time. This is one of those Mr. Wizard type science experiments that they used to show on TV, though it is extremely dangerous to do this in real life since the nails are basically exposed electrical contacts.

This type of shock isn’t so hit and miss and with enough current, it’s pretty much guaranteed to kill you. This is how the electric chair kills people, and as long as the chair is functioning properly (an important qualifier), it is extremely reliable in killing someone. The level of current and the duration matter here. A longer duration equals more heat generated equals more cooking, and hence a greater chance of death.

While getting cooked to death is a pretty reliable way of killing someone, that’s not how people usually die from 120 volt shocks. Fibrillation is what gets most folks, or something physical like falling off of a ladder and hitting your head.

37

I would guess people have not wanted to be terribly specific lest you use that specific information to go forward with your Very Bad Idea, since it is fairly obvious that you are going to dismiss the “don’t do it” part of the advice.

Personally, I think the opposite is generally true. If you think you have a solid basis for what you’re saying, then you say it and if you’re right there’s no reason to think the guy won’t listen. But if there’s one thing that makes people likely to “dismiss the “don’t do it” part of the advice”, it’s refusing to provide any basis for what you’re saying and rather just saying “hey, you probably don’t know what you’re doing anyway, so just stay away.”

38

While getting cooked to death is a pretty reliable way of killing someone, that’s not how people usually die from 120 volt shocks.

My understanding was that sometimes the shock itself makes people freeze in place, which is then long enough for them to get “cooked to death”. But you could be right about that - I don’t really know much about the relative prevalence of one type of harm vs the other.

39

Since an electrical engineer has told you this method could provide false information, I’ll ask again: At this point, what are you wanting from this thread?

And what more do you want than, “touching live wires can kill or severely injure you” in terms of specifics?

40

Another issue: If you don’t know what a particular bit of wiring does, then you also don’t know who put that bit of wiring in, or whether they were following the standards. Standards-compliant wiring isn’t that hard to work with, and an amateur can fairly easily learn to do it. Non-standards-compliant wiring is much harder, and if that’s what you’ve got, then you have a mess that needs a real professional to fix.