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I've found this image that perfectly illustrates my shower. I've read somewhere that the resistance is insulated so even if it touches the water, it doesn't conduct. However, as you can see, the terminals are exposed, and also there are cases when the resistance breaks in the middle, exposing the conductible material to the water.

Why is it that I don't get shocked?

electric shower with resistance

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This type of shower head is used in Central and South America and so other parts of the world and is sometimes called the "suicide shower" by those who visit those countries.

What you see is the uninsulated conducting element which make the transfer of heat from the element to the water to be heated efficient.
It is thus totally unlike the sort of heating element you might find in an electric kettle with there being a layer of insulator between the heating element and the outside world.

The shower works at a mains voltage of about 220 V and so there is a possibility if getting an electric shock from such a shower.
The probability of an electric shock is reduced by having an earth wire (green-yellow) dangling in the water which is passing through the shower although many installation do not have the earth wire connected.

enter image description here

The water comes in through an inlet passes the earth wire and goes into a chamber which is full of water in which the water heater is immersed.
Water pressure pushes a plunger which then activates a switch so that a current passes through the heating element and so the water is heated.

This YouTube video gives you a detailed description of the construction of the shower head showing that it can potentially be dangerous.

I cannot find any evidence of the use of a 1:1 isolation transformer and would expect that an RCCB (residual current circuit breaker) would trip with such a shower head because the live and neutral currents would most probably be different.

If you Google "suicide shower" you will find many reference which explain how to make using such a shower safer.

So you do not get a shock because the water which comes out of the shower is at earth potential.

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    $\begingroup$ I've already seen electric showers working without the earth wire! $\endgroup$ – Diracology Oct 13 '17 at 22:10
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Clearly, the water may be in direct contact with the 220 or 230V phase line voltage inside the shower head. But normal tap water has a high resistance, and this resistor (of the water touching the body) is in series with a user's body resistance. It is not (directly) the voltage that is dangerous, but the resulting current that may flow through the human body. The danger starts at ca. 10-30mA. So the total resistor (body + water) must be greater than ca. 20000 Ohm. Tap water has a higher resistance even for the short distance between the wire contact zone and the shower outlet, whereas a human body's resistance (salt, ions, water) may be as low as 500-5000 Ohm @ 230V, but is in series with the high water resistance.

Furthermore, the water with the 3 power contacts in the head forms a voltage divider that does not feed the full 230V into the part of the water that leaves the shower head.

Answers to the comments:

In the first picture, there is no insulating to be seen between conducting metall and the water. The junctions are soldered and/or crimped without any insulating coating. The coiled heating wire itself is neither insulated from the surrounding water.

A simple 50 or 60Hz transformator that would insulate the shower head circuit from the main circuits is much too expensive, heavy and bulky to be part of these simple showers, given the needed power is in the kW range.

Heating elements for conventional kettles, washing machines, dish washers, water boilers etc. are almost always of a type with full insulation between the metal parts connected to 230V and the water. Only in recent years there are types of electronic tank less water heater or flow through heaters where the conducting heat element is in direct contact with the water in order to improve speed and efficiency and to avoid lime stone coatings (thin wire expanding and contracting by heating/cooling down).

There is no galvanic insulation, there is no hollow wire, the terminals are not insulated by a hollow construction. The full mains voltage is in contact with the water.

The green yellow earth wire provides protection against cases when the conductivity of the tap water is too high (= resistance too low) to be harmless. The mandatory standard 30mA RCD switch trips the mains if the difference between phase and neutral becomes greater then 30mA, what could happen in case of contamination of the tap water with detergents, sewage water, sea water, or minerals/residues after work on the water net etc. Since this wire is much closer to the wire parts with high voltage then the user's body, it will trip before dangerous currents may flow through the user.

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    $\begingroup$ This is definitely the correct answer. The resistance is not insulated and some electric showers even work without an earth wire. The conducting element and the water are actually in parallel but the resistance of the latter is much smaller than the resistance of the former. The current flowing to the water is not enough to an electric shock. $\endgroup$ – Diracology Oct 13 '17 at 22:01
  • $\begingroup$ Yes, it is a complex parallel/series configuration with voltage dividers. If the water has low resistance, the dangerous current leaves the wire incl. the phase terminal (i.e. at ca. >25V up to 230V), then flows through the water to the shower head, into the strings of water formed by the tiny holes in the shower head, then into the body of the user, then partly back through some water strings and partly through the water leaving the sink and through the moistured air back to the ground. $\endgroup$ – xeeka Aug 9 '18 at 8:01
  • $\begingroup$ see also electronics.stackexchange.com/a/454440/168208 From the comments it can be concluded that not many people have knowledge about those bare wire heating elements. $\endgroup$ – xeeka Aug 25 at 20:40
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What is seen is the outer surface of a hollow cylinder. All the conducting elements throughout must be insulated from the outer metal. The cylinder is made of metal because metal is a good conductor of heat. It is a similar construction as an electric kettle:

Many heating elements use Nichrome, 80% nickel and 20% chromium, wire, ribbon or strip. This material has relatively high resistance, and therefore is an ideal material. A protective coating of chromium oxide forms when heated for the first time and beneath this protective coat no oxidation can take place. This oxide coating prevents the wire inside the application from burning away or breaking. In most heating elements, the element is well insulated and fully embedded into an outer copper housing which is chrome plated to help delay corrosion from the water surrounding it, which is heated by the element.

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  • $\begingroup$ but what about those terminals exposed to water? and what if the metal breaks and unveils the conducting material inside the isulating layer that was outside? $\endgroup$ – Margareth Reena Oct 11 '15 at 5:17
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    $\begingroup$ They are not terminals. Their are hollow conduits of insulated wires. They are metal for the same reason the whole tube is made of metal, to survive the high heats from the heating part of the element, and to last longer. $\endgroup$ – anna v Oct 11 '15 at 6:04
  • $\begingroup$ Sorry, I can't understand. Doesn't electricity passes inside the big resistor that's shown in the photo? The only way for electricity to get there are by those 3 'terminals' I see. What's happening? $\endgroup$ – Margareth Reena Oct 11 '15 at 6:17
  • $\begingroup$ Can you not touch the wire coming to the lamp on your desk top? Why? it is insulated on the outside, and in addition if you cut it when off power, you will see inside two or three insulated thin wires and each is carrying current/electricity. Insulation makes it safe. What you see in the picture is that the insulation of the heating element inside is further covered by a metal tube, all the way even to the terminals which are hollow and carry insulated wires which transferthe current to the heating element. Maybe you should read through howequipmentworks.com/electricity_basics $\endgroup$ – anna v Oct 11 '15 at 6:26
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    $\begingroup$ BTW, you probably have a galvanic isolation on top of that, i.e. a "transformer" of 220V to 220V. You can get shocked only if you get part of a circuit. When you touch the inside of a plug your house close the circuit with delivered current through ground. But the downstream-transformer circuit is totally out of your home circuit, so that there is no way you can be part of this circuit excepted if you touch it with both hands. $\endgroup$ – Fabrice NEYRET Oct 30 '15 at 16:24

protected by Qmechanic Jul 18 '16 at 9:32

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