Improvised immersion

[CrimpJiggler]

NOTE: I'm not planning on making one of these since they are clearly dangerous as hell, I just want to know how it works because although I have knowledge of basic electronics theory, when it comes to practical matters, I'm not very knowledgeable at all.

Heres is an improvised immersion heater that was confiscated from inmates in a German prison:

that looks like the absolute bare minimum immersion heater and is clearly dangerous as hell but I'm wondering how exactly it works. Its connected directly to a mains plug so there will be 240V AC current flowing through it. I see that the cord is stripped at the end, revealing a blue and a red wire. I'm guessing one wire is for current travelling down the cord (away from the plug socket) and the other wire is for carrying current back to the plug socket. The red and blue wires are then stripped and the exposed copper strands appear to connect to 3 razor blades. I don't know what that rope in the middle of the blades is for, maybe just a separator to prevent the blades from touching each other.

How exactly would a device like this work? Does current travel from the red wire, into one of the razor blades, then to the 2nd razor blade, then to the 3rd razor blade then to the blue wire which carries the current back to the mains socket? Also, how exactly does this device produce heat? I know that the heat is generated by the razor blades but razor blades are made of steel or some other highly conductive alloy so I wouldn't have expected much heat to be generated when current flows through. My understanding is that resistance is required to convert electrical current into heat.

 

[BobK]

It works by producing heat when a current is flowing through a reistive element, the razor blades. By the way, current does not flow in wire and out the other, it alternates between the two, which is why we call it alternating current.

Bob

 

[duke37]

The resistance which generates the heat is the water itself.

The actual value of the resistance depends on the purity of the water.
There is likely to be a lot of electrolytic corrosion of the razor blades and the water can conduct to elsewhere, giving dangerous voltages downstream.

 

[CrimpJiggler]

It works by producing heat when a current is flowing through a reistive element, the razor blades. By the way, current does not flow in wire and out the other, it alternates between the two, which is why we call it alternating current.

Bob

AC confuses me a bit. I know how AC generators work and thus, why the current alternates but I'm confused about how it operates in a circuit. With a DC current, you need two leads, one connected to the positive terminal, one to the negative terminal. With AC do you still need 2 leads? I know that in AC, the positive terminal becomes and negative terminal, then back to the positive terminal hundreds of times per second (well, depending on the frequency, I don't know exactly how many hertz the AC that comes from the wall is) but if I was to hook up a single, dead end wire to one of the terminals, current would still flow wouldn't it? With DC, you need a complete circuit connecting the positive terminal to the negative terminal but with AC, I'm thinking you don't need that because if you connect a wire to one terminal, that terminal alternates between negatively charged and positively charged so electrons from the wire will travel back and forth.

I've never actually stripped a power cord down before but I see that all plugs have at least 2 prongs. I'm guessing each prong connects to its own wire. Why 2 wires? If it was DC that came from the socket in the wall, then I'd understand because DC will only flow if theres a complete circuit connecting the negative and positive terminals. With AC couldn't you just run a single wire through the electronic device, without bothering to make the other end of the wire lead back to the electrical outlet? Is it because electronics devices generally to convert the AC to DC before they can use it? Thats one of the things that fascinates me about this prison immersion heater. It runs on AC. Sorry for the flood of questions but are there commercial electronics devices that also run on AC or do they all use DC?

 

[BobK]

AC also needs a complete circuit in order for current to flow. It there were a flow of current in a single wire, where would the electrons go when they hit the end? The point is that there is nowhere to go, then therefore the they would have to pile up. But they can't do that because the repel each other, which prevents them from moving at all. Actually, (and I am not certain of this) I think they would move a microscopic distance back and forth as the voltage changed, but that would not create enough current to do anything.

Bob

 

[CrimpJiggler]

AC also needs a complete circuit in order for current to flow. It there were a flow of current in a single wire, where would the electrons go when they hit the end? The point is that there is nowhere to go, then therefore the they would have to pile up. But they can't do that because the repel each other, which prevents them from moving at all. Actually, (and I am not certain of this) I think they would move a microscopic distance back and forth as the voltage changed, but that would not create enough current to do anything.

Bob

They wouldn't go anywhere but the negatiive charge would build up in the wire. If you hook a wire up to the negative terminal of a battery, the wire becomes negatively charged because the electrons from the negative terminal flow to the wire and spread out to reduce the charge. Conversely if you connect a wire to the positive terminal, electrons from the wire flow to the positive terminal to try and neutralise the charge. If I hooked one of the battery terminals up to an electroscope:

I'm fairly sure the flaps of the electroscope would spread apart since the aluminum foil (or whatever material the flaps are made from) become charged and repel each other.

In a DC circuit, if there is nowhere for the electrons to go, no current can flow because there is no path back to the other terminal and thus, no way for the charge to neutralise itself. But with an AC power source, the terminal that you connect the wire two alternates between positive and negative so electrons will flow into the wire when its negative, then out of the wire when its positive. I'm just speculating here though, I may have the wrong idea but I feel pretty confident that my theory is correct in this case.

EDIT: Ah I think I see what you mean. I was reading about how AC electrical outlets work there and I see that one of the two prongs is called "hot" and the other is called "neutral". All I know is that neutral leads to the ground. I'm guessing this mean that the hot wire is the only one thats actually connected to the power source and the neutral wire just leads the input current to the ground? So theres no loop at all, the situation is similar to this dead end wire scenario I was talkiing about, only different being that in this case the end of the wire touches the ground. In this case the electrons do have somewhere to go (the neutral ground can absorb many electrons) so the charge doesn't build up at the end of the wire. Like you say, that charge buildup would oppose the flow of current because when electrons reach the end of the wire, they'd repel other electrons thereby reducing the number of electrons that can flow through the wire.

 

[(*steve*)]

In order to "do electronics" we need to make a number of assumptions so that even simple things like Ohms Law works.

The electroscope is outside of that. It is physics, the simple rules of electronics do not apply.

Yes, with AC there is a loop. Simply speaking the two wires that come out of the ends of your bar heater and go to a plug in a wall can trace a circuit back to something which completes that circuit and which forces current to flow. In the normal case that is a transformer, but conceptually, those wires could lead back to the generator supplying the power.

In the case of one power conductor being grounded, the common ground is your other conductor. In actual fact, the ground is a reference that exists more for your safety than for te return flow of power, because there is a neutral conductor.

 

[CrimpJiggler]

steve: Now I'm confused again. So lets say I have a plug socket:

the top slot is the ground wire so I'll ignore that. Lets say the hot wire is the left slot and the neutral wire is the right slot. The transformer outside the building supplies AC current to the hot wire, into the electrical device (lets say a toaster). The other end of the toasters heating element must be connected to the neutral wire. Does the neutral wire lead to the ground or back to the transformer? If its to the ground then thats not really a loop is it. If its to the transformer, then why do all the tutorials I've read say it leads to the same place as the ground wire?

 

[BobK]

Because it leads to both! The neutral and ground wires are connected together at the fuse box. Both are connected to the ground, through a large copper stake, as well as to the transformer. The reason for having the seperate ground connection is so that if the neutral wire happens to be disconnected, you would not be electrocuted by touching your refrigerator, and completing the circuit to ground.

Bob

 

[duke37]

That looks like a UK socket.

Part of the loop is the supply transformer winding. This would work without any earth (ground) connection but consider what would happen if there is some leak through the transformer from the 11kV or 33kV supply. That would curl your hair!

For safety, one output connection of the transformer is connected to earth. This is done in different places in different countries and in UK it is done at the transformer and every house. So you get neutral and live (hot).

Everything metallic, water pipes, gas pipes, central heating, sinks etc are now bonded together so that there will be no voltage differences between appliances which could give a shock.

The neutral is on the left of the socket.