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There are some interesting links from that site, although I noticed a few inaccuracies on some of the websites referenced there. The TT, TN-C etc. systems mentioned are now the standard "official" designations used in the U.K. and Europe. The first letter indicates the type of grounding at the supply, and for all public supplies in Britain is T, meaning that one pole is permanently grounded (T for "terre" -- earth in French). The second letter shows the type of grounding at the customer's installation: T for a connection to a local ground rod, or N for a connection to a conductor provided by the utility company. The remaining letters, if any, indicate the arrangement of the neutral and protective ground wires of the supply: C if combined, S if separate. Some of the systems listed correspond with the arrangements you'll find in the Technical Reference Area here. Diagram #1 is known officially now as a TN-S system, i.e. installation ground is to a conductor provided by the power co. and the neutral and ground are kept separate throughout (except where the star-point of the xfmr is grounded, of course). Diagram #2, our PME (Protective Multiple Earthing) system, is designated TN-C-S as the neutral/protective ground are combined on the distribution network and separate within the house. Diagram #3 represents the TT system where the house ground is solely to a local earth rod, and the resulting high loop impedance means that a RCD (GFI) is needed. (Diagram #4, representing a now obsolete system would also be classed as TT.) All three of the systems TN-S, TN-C-S, and TT are used in Continental Europe. A normal American residential service is similar to British PME, and would be classed as TN-C-S under this designation system. [Edited for a case of "finger-trouble" typing the URL link!] [This message has been edited by pauluk (edited 05-03-2002).]
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More data. The electric showers here in Brazil sometimes use 8,000 watts or even more. There are two poles: one is + and the other is "neutral". The neutral is grounded at the entrance of the house (the panel). In this way the whole house is grounded there. The showers are made of plastic but some are metal. They have three wires, one of them is the ground. They connect this ground to the neutral pole (ground) but some electrician say that they don't have to be connected noweher because there is already a neutral, ground pole... I think I am going to put a rubber mat on the floor... I also notice that when left on for long time the wires get a little warm... What do you all think?
mvp1
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Several points strike me here.
First, the metalwork of the shower unit MUST be grounded for safety, otherwise a fault in the heating element could energize the casing. The fact that one connection to the heater element itself is a neutral, does not remove the need for the ground on the metal casing. The "electricians" who tell you this do not seem to have a proper understanding of what is going on.
Second, even where they do connect the ground terminal on the shower, I would still not be at all happy about just grounding it to the neutral. The neutral wire may be grounded at the service entrance, but the result of a loose connection on that neutral could be lethal. The ground terminal on the shower should be run separately back to the ground busbar at the main panel.
On the power ratings, are you certain that units of 8000 watts or more are used on 120 volts? That's a very heavy load which would draw approx. 67 amps and necessitate the use of very large cable. Maybe these higher-power showers are limited to houses with 3-phase power or to those areas of Brazil where 220V supplies are usual?
Cables feeding high-power devices like this will get warm over a period of time, but whether the heat is excessive is difficult to say without actual seeing the installation.
If you can check the power rating of your particular shower and the size and length of cable feeding it, we'd be able to tell you if it's large enough or not.
I'm not sure how your cables would be sized in Brazil -- probably either AWG (American sizes) or square millimeters (European).
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Many thanks. This is becoming interesting. One electritian told me that he could ground all three showers I have in the house. Hed also told me that I could connect them in 220 volts if I wanted and not in the 127 volts I have them now (apparently the electric wiring in the house will permit this). The way he wanted to ground each chower was to put three rods on the ground close to where the showers are and run the ground wire from each shower there. I will ask about running them to the entrance frame which is more distant. I will now look at how the wires are rated in Brazil and the distances. Yes they have 8000 watts or more, the smaller plastic ones have less and I can connect them in 127 or 220 (for some reason the electric here is 127, not 110 oe 120 - don't ask me why). Many thanks!!! Any thoughts or suggestions will be very welcome!
mvp1
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Marcio,
O.K., the information you have obtained now is very helpful and has told me the supply arrangement to your home.
The nominal 127-volt level was quite common throughout Continental Europe years ago (including Portugal, which probably accounts for its use in Brazil).
The fact that you have 220 volts available indicates that you have what is known as a 3-phase supply. These are very rare for residential use in America or Britain, but again, quite common in Europe.
Coming into your house from the street will be 4 wires: 3 phases (hot/live wires) and a neutral. Between any phase and neutral the voltage is 127V. Between any two of the three phases, you get 220V.
So for a shower designed or wired for 127V operation, it would be connected between one phase and neutral. For a shower wired for 220V use it will be connected across two phases.
The advantage of the 220V version is that for the same amount of power (watts), you need less current, so the cables can be smaller.
As for grounding each shower to its own rod, this would be effective only if the shower is fed through a device known as either a GFI (Ground Fault Interrupter) in the U.S.A., or an RCD (Residual Current Device) in the U.K. (I'm sorry I have no idea what it would be called in Portuguese.)
Without such a device, you could not get enough current to flow through the ground to blow a fuse or operate a normal circuit-breaker.
Such local grounding of a shower may be against your wiring rules (if you have any in Brazil?), but that aside it is a rather inelegant solution to the problem.
I would strongly advise you to have the showers grounded back to the main panel.
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What a big help. Yes, this is the case: I will have a choice between 220 and 127. And yes... in 127 one pole is + and the other is neutral (ground). Then as you say, if I connect the shower on 220 I will have the two poles hot? Isn't this more dangerous?... I guess then I will have to run the ground wire from the shower independetly to the main panel. The problem is that the main panel is not to close to the showers...perhaps 15 to 20 meters. Will this be OK?... You may wonder why I am abusing your patience on these issues... but I have had so many opinions here... even from electritians...And I want to do the right thing...Perhaps one of these days you may decide to take a holiday in Brazil and take a look...(hope you will take showers...) Regards Marcio
mvp1
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Marcio,
I strongly suggest that you have a Qualified Electrician look over your installation. This is not something that we should be delving into too deeply here. We are happy to help with general safety information but must stop short of supplying detailed How-To instructions.
Good Luck, Bill
Bill
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Sorry if what I am doing is not allowed. But it seems that I am so close to finally having things clarified for me, after I have been searching for it for a long time (including consulting with electrical contractors and electricians here), that your intervention at this point seems very unfair to me. In case you are wondering I am not here to get anything for free. I am here because I genuinelly felt that I needed good advise in the midst of so many opinions here where I am. Regards.
mvp1
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Firstly, congratulations for this site! Well, it is very interesting to find here something related to Brazil - which since 1980 doesn´t follow NEC. The related installation - 2 wires for a 127 V electric shower - was used (officially)till 1980, because in this year was issued a new Electrical Code, (the previous one was issued in 1960) that stated for areas with humidity (kitchen, bathrooms, outside areas), the use of a 3 wire system, 1 of them exclusively for grounding (colored green with yellow stripes) and the circuit has to be protected by one residual differential circuit breaker - called "DR" - similar to your american GFCI. But, it stated that for new erections - not to the old houses. The electric showers since that were manufactured with 3 wires, but as eletricians were used that 2 wire system for a long time, it is possible to find today a lot of houses with a 2 wire internal distribution system - including the showers circuits. Adding this, old houses had metallic water pipes, but newer ones use plastic water pipes. We can say that still today the "culture" is that only 2 wires are enough to "run anything". Although electricians need to get an official certificate, it is very common to find illetrate people doing residential electrical services (home owners don´t use to ask for the official certificates for such "small and low cost jobs"). Electric showers in Brazil - the highest is 5500W 127 V. The wires in Brazil since 1980 are sized in mm2. Our code follows IEC 364. As the previous messages say, it is necessary to take extremely care when contracting a person that calls himself as "electrician" in Brazil.
[This message has been edited by roadie (edited 08-12-2002).]
[This message has been edited by roadie (edited 08-13-2002).]
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Yes... the sitution is like the one you described here in Brazil. Thanks to this list and the help I got here I just contracted an electritian to do things right: the connect the groung wire inthe showers to the ground on the neutral in the frame of the electric company. I am doing the same with the ground wire in computers. The old houses here still have the two holes outlets. I know that things are changing...slowly. Thanks to all of you.
mvp1
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