Safety in electric showers

The most important reason is that the electrical wire that gets hot and hence heats the water, is surrounded by an electrically insulating material which is then sealed into an air and water tight metal tube. So no water gets into contact with the heating wire.

Secondly, pure water is not a very good conductor.

However, it only needs a little bit of other chemicals to make it conductive enough. So, if you wan't to electrocute the wife by dropping a mains radio in the bath - buy her some bath salts for her birthday, first ;)

Can you elaborate on what you mean by an "electric shower"?

It is vastly easier to suggest a mechanism for shock risk in a shower than to demonstrate the nonexistence of shock risks. Do you have a particular risk in mind?

Chuck

M.C.C.R. wrote:

Thanks for your reply. With "electric shower", I mean the kind that are vastly used in Latin America. For example, the famous Lorenzetti

The risk I have in mind, is that a normal day, after turning on the shower to take a bath (or maybe being one's wife at the shower, as Sue suggest :-) one can get a very dangerous electric shock. I think it could be fatal in that case, being naked and surronded by water. M.C.C.R.

Thank you for the additional information. I checked the Lorenzetti web site but didn't learn much.

Normally, the heating element in a water heater is enclosed in a grounded, metal case. If there is a short from the heating element to the case, a circuit breaker or fuse should interrupt the circuit quickly. Assuming, of course, that it has been installed properly.

In terms of safety, it would seem that this system is as safe (or unsafe) as large tank-type water heaters.

I'm not so sure about the effect of impurities in the water. If the water's conductivity is very poor, current is going to prefer passing through the body to going around the body through the water. In salt water, for example, the body's resistance is so much higher than the surrounding water that electrocution is much less likely.

Chuck

M.C.C.R. wrote:

Am I seeing this right? On these Lorenzetti's, up to 220 Volts is actually brought into the shower head, in the shower stall itself?

I'm comfortable with electric hot water heaters, but I don't want to be anywhere near 220 Volts when I am naked and dripping wet in the shower.

Beachcomber

Perfectly normal, in the UK at least. Although in the UK it will be earthed and every metal pipe will be bonded to its earth locally.

The water heater in the shower will typically be 7 -9kW - possibly a bit much for 110v in the US?

Until recently, these were commonly a DIY install - with the DIY'er being left to work out what to earth or not..plus having to lay a dedicated circuit back to the main house distribution box, add a circuit breaker, etc..

Personally, I prefer a nice long soak in a bath to a quick shower...

Wait a sec, do I understand the question?

The heating wire is surrounded by water (tap water is not so pure it doesn't conduct.) The case is grounded. The incoming water pipe is grounded, and full of water that is also a ground conductor. The drain is grounded.

If there is a loose source of current (water heater or spouse) would it not follow the easiest path to ground? Which would not include a body unless the current goes to it first, then to the water.

So I conclude, don't touch electrical items when in the shower, but if it falls in the water it's not so bad.

RickR

Probably not if you mean the heating element itself. It would quickly boil the water off as steam. There may be a ceramic insulator between the heating element case and the element wire. Something to transfer heat but not electricity.

(tap water is not so pure it

Correct.

Correct.

Could be. Could be plastic. 240 VAC tank type water heaters in the US do fine with plastic pipes.

Could be. Could be plastic.

The fault mechanism would most likely be a short from the heating element to the water. That would probably require that the grounded metal case be breached, but unless it completely disappeared, it is difficult to imagine current ignoring that part of the metal case that is intact and flowing instead through the hole into the water and down the drain. That would be truly amazing!

Good conclusion.

but if

If by "it" you mean the appliance, and by the water you mean the shower, I would panic. If it is a bathtub, I would also panic. Most electrical appliances are nowhere near as safe as a metal-jacketed water heating element in a properly designed and installed system.

Chuck

... Perhaps you could answer a few UK bathroom questions for a dumb American who is only familiar with the American way (i.e. having a big standing 40-80 gallon tanks of hot water, heated to the max, with gas or electric, and ready 24 hours per day.)

It sounds inefficient, but it really is not.

What about the hot water faucet for the washbasin or sink? Is that centrally heated or does it come off the shower heater somehow? Or is just cold water available for the most part?

Even at 220 volts, every time the shower heater kicks at 9 kiloWatts or so... That's still a hell of a lot of current... Wouldn't there be a demand problem say in an apartment complex where everybody turns on their shower during the morning hours? I would think the lights would be dimming all over the place.

(Just as an aside... US Electric water heaters are also generally

9000 watts total, but most come with two 4500 watt elements and only one is switched on at a time)

Beachcomber

The shower heater output goes *only* to the shower rose - without any valves in the way. Flow is controlled by varying the water flow into the heating tank within the unit.

The following link shows how central heating systems provide hot water to the normal taps in the house:

The hot water tank, where fitted, normally has one or two electric immersion heaters, to heat the water when the central heating system isn't running. Where the house has electric central heating, one immersion heater is at the bottom of the tank and is fed from the cut-price off-peak side of the electric meter, giving a tank full of hot water, heated overnight. The top heater is fed with full-price electricity, to make up any shortfall from the overnight heating cycle.

Small electrical heaters, like the shower water heater and also a kitchen equivalent, are fed via their own dedicated circuits from the main distribution point. AFAIK,IIRC, my flat was typical and had a 60A supply. In these days where the house is empty all day, a couple of these small heaters provides all the hot water needed. So the immersion heaters are switched off.

I live in the middle of a National Park so have no mains gas. It's quite large, 7 bedrooms, but has a large (walk-in) fireplace in the drawing room that I keep a log fire running constantly in the winter. The back of the fireplace has a cast iron water "boiler"/heat reflector that is convection linked to produces the hot water for the house. Most older houses with fireplaces had such a "back boiler" - but real fireplaces are pretty rare these days. The hot water tank is about 120 gallons. As I have to manually move the heat reflector to vary the heat that reaches the boiler, most of the time the water is way, way too hot. Perhaps just as well it isn't linked to radiators..Mind you, it gives a nice deep, long bath...

HTH

Sue

Interesting information... It sounds like you UK residents have some choices in heating systems that we Americans mostly lack although on the East Coast of the US, one sees more of these combined heating/domestic hot water boiler systems, mostly oil-fired.

Elsewhere in the US, where natural gas is available, the domestic hot water and building heating systems are mostly kept separate. There are some hydronic boiler heating systems in newer construction, but the gas-forced air furnace is still probably the most common system installed today.

Time rate (cheap rate) electric service for residential is only available in certain markets and requires the installation of a special electric meter (usually at extra cost + a monthly rental fee).

What does a UK person typically pay for in terms of the rate for electricity?

In the US, it commonly varies from 6 cents (US) to 14 cents per kWh although some expensive markets (mostly in the Northeast) have super-expensive rates of up to 20 cents per kwH or so.

Beachcomber

UK:The special meter is installed for free - but the daytime tariff is higher with a special meter.

These are the rates for my area from a major supplier - it varies from place to place and supplier to supplier:

1st 1144 kWhr per quarter : 25.181p (0.439685441 U.S. dollars)

1144- 73268 kwhr per quarter : 13.132p (0.229297852 U.S. dollars)

Over 73268 kWhr per quarter : 2.595p (0.045311295 U.S. dollars )(also the night rate)

So you would have to use over 2000 USD of electricity a year to move off the most expensive rate.

You would have to use over 68000 USD of electricity a year to move onto the cheapest rate - although, if you have a special meter you get 7 hours of cheapest rate each night, say between 11pm and 6am.

I think I have just re-defined "super-expensive" for you ;)

This is my point. Where does a body in tub become part of the circuit? Granted the drain could be plastic and the tub fiberglass so the body would receive a voltage differential as the AC cycles, but no current to speak of. Is that enough to kill?

It doesn't take much for a potential difference to find a conductive path to ground, especially at 240 volts. I'm just surprised that the UK codes apparently allow this level of voltage in a wet environment like a shower. I wonder what the statistics are for people electrocuted or injured in UK shower/electrical accidents each year? Those bonding rules for all metal in the bathroom environment are pretty strict.

I once got the shock of a lifetime by standing barefoot on a damp (not wet) tile floor and touching a defective 120V. lamp socket. It was the fact the the current was passing through my whole body (not just my hand) that made it difficult to let go. It was very, very painful.

BTW, Prior to this, I would have never guessed that a damp tile floor would carry a current to ground.

Beachcomber

You've posed a very interesting question. Definitely not the sort of thing we care to experiment with.

With a fiberglass tub and plastic drain, a powered appliance like a hair dryer dropped into the water most probably would not trip a breaker. If the hot wires were spaced an inch apart in the appliance, there would be a strong field between those points and the field would curve outward beyond the one inch. But would the field be strong enough at six inches to even be felt by a human? Would it be lethal? My guess, and it is barely more than that, is that it would not. Also, it would depend on where it landed in the water. Most of us would react by grabbing the appliance to toss it out of the tub, which would probably be a bad move. I wonder what the safe thing to do might be. Pull the cord from the outlet? Lift the appliance out of the water by the dry part of the cord. Yell for help? Interesting.

With a grounded metal drain in the tub or maybe with a grounded metal tub, it's a no-brainer, of course. Even if the water is distilled and there is effectively no current through the water, the drain and the hot wire create an electric field in the water. The body placed in that field experiences a voltage differential between head and foot, as you suggested, which, given the resistance of the body, is enough to cause a lethal current (generally more than 5 milliamperes) to flow through the body.

I have left out that there will be two fields: one from the hot wire to the neutral in the appliance, and the other from the hot wire to the grounded drain. The latter field would probably be a lot weaker.

Chuck

RickR wrote:

The shower units are designed for such use, obviously. Such units are used all over the 220-240V world. In the UK, they vary between 7kW and 10.5kW. In some other European countries, higher power ones are used.

I was following the stats for a while, and there was around one every 5 years. Last one, cause is unknown because of gross incompetence in the investigation. (The electrical company who fitted it were initially asked to investigate, and found nothing wrong, a result which is clearly bogus as the shower had just killed someone. Any further investigation after the company had taken the installation to pieces was rather pointless. Almost certainly, the bonding had been missing or faulty as the accident would have been impossible with it.)

Well, there was a more recent one too. A guy doing a full house refurb decided to take a shower. There was no electricity in the house at the current state of refurb, so he used an extension cord from a neighbour to power the shower. As far as investigators could tell, he must have been holding the shower heater unit whilst showering, which is supposed to be fixed to the wall, because there was no sign that it ever had been. In the UK groups where this issue came up, the expression "Darwin Award" was liberally used.

Yep. It pretty much means regardless of any electrical fault, there's almost no way you can be electrocuted because there can't be any potential differences between exposed metalwork in the bathroom. It's a scheme which seems to have worked very well for best part of

50 years.

You are paying a very expensive day rate because you have different day/night tarifs. In comparison, I don't, and my continuous rate is

7.34p/kWhr (0.128 USD) for first 727kWh/quarter 6.96p/kWhr (0.121 USD) after first 727kWh/quarter

There is another higher price break, but I didn't reach it so it doesn't say what it is on my bill.

If I shopped around, I could significantly reduce these prices.

Note the "from a major supplier" - actually British Gas*.

LOL, I didn't mention the company name as it might be a little confusing for some of the readers that we in the UK buy our electric from "British Gas".

I picked it to illustrate the off-peak rate that was being discussed..

UK electrickery seems to be more expensive than the US equivalent though. But the price difference looks a lot closer than the difference between what we pay for vehicle fuel..

*I don't actually pay it as I am on a single rate tariff, as you are, from a different supplier.

Sue:

Holy cow! That is expensive... something like (US) $0.70 - $0.75 per

10 minute shower at the day rate. On the other hand, it is surprisingly cheap at the night rate. That is quite a differential.

Thanks for the info...

Beachcomber