The modern man does not know how to do without electricity in any of his occupations and even in his bath. Unfortunately, those who unwisely try to combine the two enemies of electricity and water put their lives in danger.
If we do not know how to moderate the action of water, we know how to control the strength of electricity: we have therefore designed safety equipment that eliminates risks.
The power supply under 12 Volts is called "Very Low Voltage Safety" because this voltage can not create a deadly danger for any person in good health. This is why SELV devices are the only ones admitted in volume 1 of the washrooms, except for switches and sockets.
• The 12 V circuit can not be earthed at any point and its insulation must be reinforced (in principle double) compared to other electrical circuits.
• The 12 V conductors must run in a separate pipe from the 230 V conductors and be able to withstand the heating in the vicinity of the spots
• The permissible voltage drop is 0.6 volts maximum (ie 5%), which limits the length of a 12 V connection, for example to 2.40 m for a power supply of 100 VA and a driver of 1, 5 mm2.
The 12 Volt voltage is supplied by a 240/12 V transformer, short-circuit proof, built-in or built-in, and must be class II; its power must be at least equal to the sum of the powers of the apparatus to be supplied.
• The installation of the transformer in the bathroom can only take place in volumes 2 and 3. But it must remain accessible, which implies that it can not be placed (as well as the protective devices) in ceilings and false ceilings only if they are removable; in addition, the transformer must be fixed and mounted on a part itself fixed.
• The transformer must be protected against secondary short circuits, either by an incorporated device which cuts off the current in less than 5 seconds (in the case of transformers integrated in the luminaire), or by a protective device placed on each connection between the secondary output and the power supply of a 12 V.
• The types of transformers depend on their power and their location (integrated or not with the SELV device): the electronic transformer is suitable for the integration in the base of a device of 60 VA maximum; the ballast transformer is suitable up to 100 VA; for higher power, an overmoulded transformer is used.
The toroidal transformer is used with a dimmer, but it tends to "buzz" when it is set to low power.
Given its relatively limited power, as well as limits to the length of the conductors, the use of the SELV voltage remains circumscribed to a few devices, in the bathroom, but also more and more often in the kitchen (especially in the area above the sink and around the fume hood).
• Halogen lighting is the core of the proposed 12 V switchgear, in the form of recessed or rail-mounted spotlights, or lighting rail systems.
• The bulb halogen lamps are 10 and 20 W (low pressure) and 50 W.
• Dichroic halogen spotlights, which give warm light, improve contrasts without damaging the colors, are commonly available in closed dichroic reflector spot at 20 and 35 W, and in closed dichroic reflector spot and protective glass at 20 and 50 W.
• The 12 V supply of recessed spots is done using high temperature conductors to account for the significant heating they generate. Other 12 V equipment. There are various devices supplied with 12 V DC for cars (trucks are under 24 V). These devices can be powered by 12 V TBTS, but must not be used in volume 1 of the water rooms. Powered by the cigarette lighter plug, this equipment can have an adapter (for use in a vehicle) with a SELV plug (2 lateral pins, center distance 12 mm), which can only be connected to the 12 V TBTS.
(photos / visuals: © DIY-Prod, except special mention)
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