MCB Diagram

Fuses, MCBs, RCDs and RCBOs – what is it all about????

Fuses, MCBs, RCDs and RCBOs – what is it all about????

OK so they are all there to protect, but what is the difference and what do they do?


Firstly fuses and MCBs – that is miniature circuit breakers – they both ‘blow’ when current is exceeded, but an MCB can be reset after the fault is fixed, a fuse must be replaced.
A fuse is basically a piece of wire between two contacts to make a circuit. When current flows heat is produced and the wire gets hot. If too much current it produced the wire melts and the circuit is broken. There is nothing you can do you must replace the fuse.
A miniature circuit breaker on the other hand uses an electromagnet to break the circuit if the current is exceeded. It also has a toggle on the front so that it can be reset. The MCB is generally more reliable than a fuse and reacts quicker.
The Chint range of MCBs are available from stock at Chalon Components in all curves and Amp ranges.

So that is a fuse and a miniature circuit breaker what of an RCD?

Well the fuse and the MCB will protect equipment and wiring, they will not protect people. An RCD is designed to protect people.
The residual current device monitors the current that goes down the live and neutral cables. If the circuit is healthy then the current going down the live cable will be the same as that coming back through the neutral cable. This means that the amount of current going down the earth cable will be nil and all is well.

NE2 Metal SocketIf some of the current leaks from the live to the earth the RCD will detect the difference between the live and neutral and trip. So if you are gardening and accidentally ‘strim’ the cable instead of the grass an RCD protected socket would detect the difference in current flow and trip out.
The Chint RCD protected sockets have a 30mA trip so although they will allow a small amount of leakage they will greatly reduce the risk of fatality. The plastic version can be used as a direct replacement for a standard double socket.


If sockets are fitted outside it is preferable to fit an RCD into the distribution board feeding the sockets. Great, but you’ve not got any space in the board as it is full of MCBs. Enter the RCBO – in short a combined MCB and RCD. This is the answer to the problem as they now come in single module width to fit into distribution boards.

NB3LEU RCBOThe MCB side of the unit handles the current and will trip based on a over-current whilst the RCD side monitors the earth leakage and will trip if it detects an imbalance of the live and neutral. The other great advantage of using the RCBO is that only one circuit is affected in the event of a trip – not the whole board as would be the case if using an RCD as an incoming switch on a distribution board.

Chalon Components Ltd stock the Chint NB3LEU RCBO in both B and C Curve up to 40amps.


Distribution Boards, Consumer Units or Fuseboxes

Distribution Boards, Consumer Units or Fuseboxes
The New Rules

It doesn’t matter what you call it, the box is now subject to British Standard BS EN 61439-3. Distribution boards intended to be operated by ordinary persons (DBO) and The third amendment to BS 7671:2008 (IET Wiring Regulations Seventeenth Edition). This came into effect on 1 July 2015 and requires consumer units and similar switchgear assemblies in domestic premises to have a non-combustible enclosure.
The wording of the regulation is this:

421.1.201 Within domestic (household) premises, consumer units and similar switchgear assemblies shall comply with BS EN 61439-3 and shall:
(i) have their enclosure manufactured from non-combustible material, or
(ii) be enclosed in a cabinet or enclosure constructed of non-combustible material and complying with Regulation 132.12.
NOTE 1: Ferrous metal, e.g. steel, is deemed to be an example of a non-combustible material.
NOTE 2: The implementation date for this regulation is the 1st January 2016, but does not preclude compliance with the regulation prior to that date.


Simple really, more and more fires have been found to have been found to involve consumer units. Whether that be poor workmanship or lack of maintenance, the most important thing is that if the enclosure had been non combustible or metal it would have contained the fire. Whereas the previous thermoplastic ones would melt and allow the flames to escape as these pictures show.

Damaged House boards

Does this apply to outbuildings, such as garages or sheds? Well the regulation actually uses the term ‘premises’ which brings us to the question what is the definition of ‘premises’ and what does it include? The regulation was primarily introduced to cover the interior of a house, but it is good practice to question the proximity of the outbuilding to the main house. Is it an integral garage or attached to the main building and of course does it contain anything combustible.
Regulation 421.1.201 is not intended to apply to a consumer unit that is not within a building, such one mounted outdoors i.e. the outside of a building.

But if in doubt use a metal clad enclosure!!


Damaged BoardsAll Chint Distribution Boards and pre-Assembled Garage and Shower Units comply with the Regulations. The boards have certification by 3rd Party Test Houses, copies of which are available on request.

Chalon Components Ltd are pleased to be able to offer the full Chint NX3 range of Metal consumer units from 3 ways to 36 ways, download the full brochure here.

Emas Potentiometer

Emas Potentiometer

Emas Potentiometer

Well executed 22mm Industrial Potentiometer It’s not new or groundbreaking its just well executed, the Potentiometer designed and made by EMAS.

Gone are the days of buying an electronics pot and 10 turn graduated dial from a Catalogue company and making something up, then soldering wires to it….there’s 15-25 mins wasted.

EMAS UK we stock the 1K, 5K, and 10K versions in the 100’s, single turn dial, 22mm monoblock style, standard 3 wire terminal clamps on the rear, easy to connect and use…save money and time….it just makes “cents”

Purchase here

Emas Potentiometer