Bathroom Wiring System

What Is The Specialty For Bathroom Wiring Than Others? 

Yes, I am not meaning latest fashion about your bathroom. As a talk from an Electrical Engineer, I am talking about your bathroom safety fashion from the point of Electrical Engineering. You may be thinking, why different wiring need for bathroom, what is problem with same others wiring.

From the note of expert on wiring accessories like legrand  we can quote as following that will give us basic idea about bathroom wiring exception.

“The wiring regulations are very strict. Every switch or other means of electrical control or adjustment shall be so situated as to be normally inaccessible in the bathroom. The required Ingress protection is managed through a series of defined zones progressively from the bath or shower. Pull cord switches are allowed, shaver sockets with isolating transformers are also allowed but should conform to BS EN 61558-2-5”.

Especial Zone Rules In Bathroom System

Especial rules apply to bathroom wiring where the room is divided into different zones are shown in the above figure:

Zone Bereich 0: Electrical equipment are not allowed. Only special SELV-devices, max.12V AC or max. 30V DC are allowed. The power supply for these SELV-circuits is not allowed in Bereich 0 and in Bereich 1.

Zone Bereich 1: Only fixed installed electrical equipment for hot water production and SELVor PELV –devices (max. 25V AC or max. 60V DC) are allowed. The power supply for the SELV- or PELV -circuits has to be installed outside Bereich 0 and in Bereich 1.

Zone Bereich 2: Only Electrical equipment supplied by SELV- or PELV (max. 25V AC or max.60V DC) are allowed.

Why Bathroom Wiring Need Especial?

Simple, the reason is safety. Water is very good conductor to passes electricity, even an insulating material become like a conductor when water is presence. That’s way bathroom needs such a wiring where there is no chance to electric shock.

Situating the all switches and electrical stuff inside bathroom in a safe distance is possible to reduce electrical shock, But  it will be more reliable system, if no presence of shock-able voltage there.

To ensure the bathroom wiring shock-able free voltage, need an Extra Low Voltage system which is electrically separated from Earth in such a way that a single fault cannot give rise to the risk of electric shock- is known as SELV (Separated Extra Low Voltage).


How SELV Works For Bathroom Wiring System?

To ensure the direct and indirect contact protection Separated Extra Low Voltage (SELV) and Protective Extra Low Voltage (PELV) are used in bathroom wiring system.

For a Separate Extra Low Voltage system the source of power shall not exceed “extra low voltage” i.e. 50V ac or 150V dc between conductors and earth.

The SELV circuit is supplied by an independent source like batteries or diesel-driven generators or by a safety source like- supplies obtained through an isolating transformer in which there is no connection between the output winding and the body or the protective earthing conductor.

In the SELV system all components including conductors, switches, relays etc. are physically separated from those of any other live system.

Conductors of the SELV & PELV circuits may be contained in multi-conductor cables or with an additional insulating sheath.

Finally remember and check again the bathroom wiring  standard BS EN 61558-2-5 what deals with the safety of shaver transformers, power supply units incorporating a shaver transformer, and shaver supply units. Shaver transformers incorporating electronic circuits are also covered.


Selecting and installing electrical equipment

Electrical equipment, forming part of an electrical installation, shall be selected and installed to:

  1. operate in a safe and reliable manner in the course of normal operating conditions
  2. not cause danger from electric shock, fire, high temperature or physical injury in the event of reasonably expected conditions of abnormal operation, overload, fault or external influences that may apply in the electrical installation
  3. be installed in accordance with the manufacturer's instructions.

In a separated extra-low voltage (SELV) system the low-voltage output is electrically separated (galvanically) from earth and other systems. Therefore, a single fault cannot create a risk of an electric shock. There should be no provision for earthing of an SELV circuit.3)

In certain locations, e.g. swimming pools or for medical apparatus it is the only measure permitted. However, because there is always a risk of electric shock then the requirements can be even more stringent, e.g. nominal voltage limited to 12 V AC or 30 V DC.

SELV voltage can be generated for instance from a battery.

However, it can be also generated by means of a SELV transformer, but the construction requires high-integrity equipment and materials. This is in order to ensure adequate isolation from the primary voltage (mains voltage) which is much more dangerous. 

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