Your Distribution Board / Consumer Unit
The Distribution Board or Consumer Unit is the box where the power comes into the house and is then distributed (hence the name) to the power and lighting circuits.
OK, now you know what I'm talking about.
A regular Consumer Unit, note the labels under the breakers identifying the circuit controlled by each.
The Consumer Unit contains a number of safety devices and features which will be discussed here :-
· The Earth Leakage Circuit Breaker (ELCB), sometimes known an RCD (Residual Current Device) or an RCCB (Residual Current Circuit Breaker). Often the device is just referred to as 'The Trip'. The ELCB provides protection from electric shock caused by 'earth leakage' faults, either through a person or through a damaged appliance (maybe damp inside a washing machine). The ELCB is often combined with the 'main' circuit breaker to provide protection from both overload and earth faults.
· The Miniature Circuit Breakers (MCBs) that protect each circuit. These perform the same role as the fuses that were installed in older Consumer Units, protecting the cables from excessive current.
· Finally the MEN (Multiple Earthed Neutral) or PME (Protective Multiple Earthing) link. The MEN link provides additional safety by guaranteeing a low resistance path from the Protective Ground (earth) terminal to the neutral of the transformer. This will ensure a rapid trip of the circuit breaker in the event of a Live to Earth fault and provides a valuable back-up to the ELCB. But see MEN / PME Link below.
Correct Wiring of a Simple Installation
The diagram shows the simplest of domestic installations, with a single lighting circuit, a single power circuit, a water heater and a spare circuit breaker for future use. This diagram should form the basis of your electrical installation.
** Utility Isolator and Fuse. These are often located in a little "house" at the bottom of the transformer pole (if they are installed at all). The electrical position (before or after the meter) seems arbitrary, the diagram show the 'correct' (Western) installation. The isolator is often a ceramic 'knife' type. Only operate this isolator if absolutely necessary, wear rubber gloves (regular Marigolds are fine if dry and un-damaged), don't touch the exposed 'knives' (they 'should' be on the isolated side, but again TiT).
The 80 amp (depends upon the 'size' of supply you have specified) HRC fuse in the Live between the Distribution Transformer & the Kilowatt Hour meter is protecting the Consumers Mains, which in this case, cannot be any smaller than 16 mm2 copper wire. The fuse must be a BS1361 (British Standard) as this fuse will limit prospective fault currents to below 6kA (BS88 fuses only limit to 10 kA minimum for a max 160/200 amp fuse size). Subsequently, all downstream MCCB's must have a minimum interrupt capacity of 6kA when using a BS1361 fuse. If BS88 fuses are used, the minimum interrupt capacity of downstream breakers must be 10kA..
All ‘power points’ should have an earth pin that is electrically connected to the residential earthing system as shown in the diagram. Some appliances that plug into these outlets are supplied with a 2 pin plug. These are normally ‘double insulated’ & do not require to be earthed, most of these appliances are plastic.
Examples of such appliances are;
Modern television sets.
Modern electric hand drills.
Most non-metallic white goods (with the exception of electric kettles).
All other appliances that have metallic enclosures must be earthed, for example;
Electric cooking appliances.
Air conditioning units
Desktop Computers (laptop computers usually do not require earthing)
All electrical lighting that is metal clad, must be earthed if such lighting is installed at a ceiling height of less than 2.5 metres (8 feet) from the floor.
MEN / PME Link
The use of an MEN link is an important safety feature and is required by Thai electrical regulations.
HOWEVER many rural areas have not implemented the multiple earth system as yet. Your electrician or electrical inspector will be able to advise whether the MEN system has been implemented in your area and indicate the requirement for the MEN link.
The minimum wire size of the MEN link should be at least the same size as the largest ‘active’ supply conductor.
The earthing electrode must be a minimum length of 1.5 metres and be driven into the earth to at least 1.4 metres so that 100mm of earth stake protrudes. It should be ‘copper sheathed steel core’ or of electrical grade solid copper with a minimum diameter of 12.5mm (0.5 inches).
Generally, the Main Earth cable should be the same size as the largest ‘active’ supply conductor.
The Consumer Earth should be electrically & mechanically bonded onto the Main Earth stake with an appropriate clamp, the connection at the stake should be painted with an Acrylic paint to inhibit oxidisation of the connection.
The Main Earth connection should be readily accessible at all times.
Although not required by the regulations you may wish to install individual Earth Leakage protection devices for each Power / Lighting Circuit. This is because some appliances like old refrigerators or air conditioners have a high residual earth leakage & can therefore cause nuisance tripping. Would you want your whole electrical supply to trip because of one appliance? People who have their whole house supply protected by one earth leakage device, tend to increase the trip current to overcome this nuisance tripping. This ultimately defeats the purpose of Earth Leakage protection. It often ends up being turned off or removed.
You may also want to protect only half of the lighting circuits by an ELCB. In the event of a fire or a similar emergency, it is not recommended that all of the lighting circuits be disabled. How can you find your way out if all the lights trip on earth leakage?
A More Elegant Solution, The Split Service Consumer Unit
As previously indicated it may not be desirable for all appliances and lighting to be protected by an ELCB. Some equipment is naturally 'leaky' other equipment could be adversely affected by a 'nuisance trip' (your freezer for example).
The Split Service Consumer Unit addresses these issues.
The diagram shows the internal wiring of a Split Service unit. It looks a lot more complex than the 'simple' unit, but it is really just two simple units side by side, only one of which is protected by an ELCB.
NOTE that the neutral bar is split by the ELCB, this split is vital for correct operation of the ELCB. Many modern consumer units have the neutral bar already split, you must simply remove a link in the bar in order to configure it as a Split Service unit.