Sunday, March 19, 2023


Bathroom Wiring System
Fig: Architectural Drawing for a bathroom wiring

What Is The Specialty For Bathroom Wiring Than Others? 

Yes, I am not meaning the latest fashion in 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 is different wiring needed for the bathroom, what is the problem with the same wiring.

From the note of experts on wiring accessories like Legrand, we can quote as follows that will give us a basic idea about bathroom wiring exceptions.

“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 is not allowed. Only special SELV devices, max.12V AC or max. 30V DC is 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 SELV or PELV –devices (max. 25V AC or max. 60V DC) are allowed. The power supply for the SELV- or PELV -circuits have 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) is allowed.

Why Does Bathroom Wiring Need Especial?

Simple, the reason is safety. Water is a very good conductor to pass electricity, even an insulating material becomes like a conductor when water is present. That’s why the bathroom needs such wiring where there is no chance of electric shock.

Situating all switches and electrical stuff inside a bathroom at a safe distance is possible to reduce electrical shock, But it will be a 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 that 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 Systems?

To ensure direct and indirect contact protection Separated Extra Low Voltage (SELV) and Protective Extra Low Voltage (PELV) are used in the 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 which 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 the earth and other systems. Therefore, a single fault cannot create a risk of an electric shock. There should be no provision for earthing of a SELV circuit.3)

In specific locations, e.g. swimming pools or medical apparatus it is the only measure permitted. However, because there is always a risk of electric shock, 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. 

Bathroom Electrical Wiring Code

The NEC requires that all outlet receptacles in a bathroom be GFCI protected.
Outlet circuit must be 20 amps: A 20-amp circuit is the necessary amount of energy that is required to fully utilize the lighting and electrical components of a bathroom. The outlets in a bathroom should be served by a 20-amp circuit, separate from the lighting circuit, to provide power items such as curling irons, razors, and hairdryers.

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