Consumer Unit FAQs
Please have a look at the FAQs below and if your question is not here, please email us using the form at the bottom of the page.
How does an RCD work?
The working part of an RCD consists of an iron core, called a toroid, one half of which is wrapped by the live copper wire while the other half is wrapped by the neutral copper wire. Using the physical properties of electromagnetism, the neutral and live cables produce equal and opposing magnetic fields in the toroid which cancel each other out. A special switch, called a relay is connected to the toroid via third copper wire, sometimes referred to as the 'search' or 'detector' coil. During normal operation no electric current passes through this wire to the relay, because the live and neutral coils are not producing a net electromagnetic field.
When for example an issue occurs such as a lawnmower slicing the power cable, the current in the neutral cable is now greater than that in the live. The magnetic fields they produce are no longer equal, resulting in a net magnetic field in the toroid. This magnetic field creates a current which passes down the detector coil to the relay, causing it to snap open, breaking the circuit and thus cutting power to the electrical system.
Please see our section on RCDs here for more information
What is an MCB?
A Miniature Circuit Breaker (MCB) is an electromechanical device designed to protect an electric circuit from over-current - a term to describe an electrical fault caused by either overload or short circuit.
Back in the day we protected against over-current by using fuse wire (indeed, we used to sell it!). The principle was fairly simple - an over-current would quite literally, 'blow' the fuse wire by rapidly heating and melting it, thus breaking the electrical connection and in doing so, protected the rest of the electrical circuit.
MCBs improve on this functionality as they are usually not destroyed during over-current so are reusable. They are also much easier to use, offering the convenience of 'on/off switching' for circuit isolation and since the conductor is housed within a plastic casing, they are much safer to use and operate.
It is important to note that MCBs do not protect humans against electrical shock caused by 'earth leakage'. This service is provided by RCDs and RCBOs.
What is an RCBO?
RCBO stands for 'Residual Current Breaker with Over-Current'. As the name suggests it protects against two types of fault and in essence combines the functionality of an MCB and RCD.
Let us first remind ourselves of those two faults:
Residual Current, or Earth Leakage - Occurs when there is an accidental break in a circuit through poor electrical wiring or DIY accidents such as drilling through a cable when mounting a picture hook or cutting through a cable with the lawn mower. In this instance the electricity must go somewhere and choosing the easiest route travels through the lawnmower or drill to the human causing electric shock.
Over-Current takes two forms:
Overload - Occurs when too many devices are in use on the circuit, drawing an amount of power which exceeds the capacity of the cable.
Short Circuit - Occurs when there is a direct connection between the live and neutral conductors. Without the resistance provided by the normal circuit integrity, electrical current rushes around the circuit in a loop and multiplies the amperage by many thousand times in just milliseconds and is considerably more dangerous than Overload.
Whereas an RCD is designed solely to protect against earth leakage and an MCB protects only against over-current, an RCBO protects against both types of fault.
Please see our complete guide to RCBOs here.
Can you use MCBs, RCBOs and RCDs in consumer units from different manufacturers?
NO – ABSOLUTELY NOT. Circuit protection devices are electo mechanical instruments designed to be used solely and specifically with the same manufacturer's consumer units, din rails and busbars.
If you purchase, for example, a Fusebox consumer unit you must populate only with Fusebox protection devices.
What is an SPD?
A Surge Protection Device or SPD is a device designed to protect your circuit from electrical surges which can be a source of constant stress for electronic components, leading to tripping of RCDs, unplanned outages and premature failure.
Please see our section on surge protection here for more information
What is an RCBO consumer unit?
An RCBO or 'Main Switch Consumer Unit' is so called because it is supplied empty of all protection devices except the main switch. Whilst it may be populated with an RCD and MCBs
It is usually populated exclusively with RCBOs but theoretically could be populate with RCD and MCBs.
Many electricians consider this the best circuit protection solution as each circuit is protected from overload and earth leakage individually, thus preventing nuisance tripping caused by earth leakage on other circuits.
What is a populated consumer unit?
Populated consumer units come with a complement of MCBs as part of the order. Each board listing will tell you the values and quantities of MCBs that are supplied with the board. These can be changed by request if needed.
How do I change the compliment of breakers on fully loaded boards?
Please place your order through the website and then email us at firstname.lastname@example.org
with your order number and list of the breakers you need. We will reply by email to confirm the changes.
What does it mean by usable ways?
Usable ways is the total number of individual circuits that may be protected by a particular consumer unit. A 14 way consumer unit, for example, allows for 14 circuits.
When designing your electrical protection scheme always allow for some redundant circuits for future additions and changes to the electrical layout.
Sales, Order and Account Enquiries
Is the item I want in stock?
As most of our clients are fully qualified electricians working to deadlines and requiring next day delivery, we stock 100% of all domestic circuit protection devices offered for sale on this website.
This includes all Fusebox, Hager and Wylex domestic consumer units, RCBOs and MCBs.
We also stock most commercial protection devices such as 3 phase MCBs and the more common panel and distribution boards.
Availability of every product is stated under the ‘Add To Basket Button’
What is the 18th edition?
The 18th Edition wiring regulations are the latest iteration of the British Standards regulations that came into effect on the 1st of January 2019. All our products are 18th Edition compliant
How do I return an item?
Returning an item to us is easy. Please follow this link to the returns section.
I need a copy of my invoice.
Please email us using the form below to request a copy of your invoice with your full name and the order number for the invoice you need.
If you require any information or advice please do not hesitate to email us using form below.
We have over 21 years' experience in supplying electrical materials to both trade and end user customers.
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