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When it comes to electrical wiring and installations, there is a lot that goes behind the work to give you a working electrical system that powers your property and all the electrical equipment in it.

Mains electricity is one of the most important parts of an electrical system and refers to the electrical supply coming into your property from the power grid.

The current flows continuously in one direction, and then the opposite, and it enters your house via a live wire which carries the inbound electricity.

The sub-main, on the other hand, refers to a circuit that comes directly from the main low voltage (LV) switchboard to the sub-main distribution panel.

Read on to find out more about sub-main, where it is used, how it is installed, how much it costs, and the difference between a sub-main and main panel:


A distribution board, also called a distribution panel (DP), panel board, breaker panel, and electrical panel, is an integral part of an electrical system and its job is to split the incoming electrical supply into multiple subsidiary circuits.

A distribution board separates the incoming supply into several sub-circuits that hold all the fuses, breakers, and other circuit protection devices within the same enclosure. Not all distribution boards are enclosed though, with some only semi-closed and others left open.

These secondary circuits will mostly be protected with a fuse or a breaker and, in the UK, they are often referred to as consumer units in domestic properties.

Although for practical uses the terms consumer unit and distribution board mean the same thing, they are not completely interchangeable.


Many people get confused between distribution boards and consumer units, and the fact that they are sometimes used interchangeably further increases the confusion.

While in practice, the difference between the two is only with reference to certain use cases, in reality, a consumer unit is a type of distribution board.

What this means is that while all consumer units are distribution boards, all distribution boards are not consumer units. Consumer units are generally found in buildings and are recognised by their metal or plastic enclosure containing several fuses and breakers.

That being said, a consumer unit is simply a specific type of distribution board that is used in typical residential and commercial settings and is approved as a safe electric panel design.


There are several common types of distribution boards that include:

Main switch consumer units

Main switch consumer units are a popular choice for single-storey houses and small flats and are one of the safest and most robust devices for incoming electricity supply.

All the circuits are completely separated and the units have a single main switch through which all the subsidiary circuits can be switched off.

Dual RCD consumer units

Dual RCD (Residual Current Device) consumer units consist of two sets of circuits protected by RCD breakers that offer dual functionality in the event of one of them not being operational.

Although a step down in terms of their protective capacity, they are suitable for certain uses and provide robust protection against overheating and electrical fires.

High-integrity consumer units

High-integrity consumer units combine the functionality of dual RCD protection with additional RCBOs (residual current breaker with overcurrent protection) and are more commonly found in larger buildings with several secondary circuits branching off of the main incoming electric supply.

Type A and Type B distribution boards

Type A and type B distribution boards offer different compatibility with certain overcurrent protective devices (OCPDs) and various configurations of busbars.

When selecting one for installation in commercial or industrial properties, in addition to determining its general operating conditions, environmental factors, and accessibility requirements, you also have to factor in certain location-specific codes and standards.

Sub-distribution or sub-boards

A sub-distribution board is essentially a smaller distribution board acting as a subsidiary to a larger one, enabling greater control and isolation of several smaller circuits and breakers.

An RCD incomer consumer unit is a common example of a sub-board that doesn’t have a main switch onboard and will usually be located on a larger distribution board that the sub-distribution board is attached to.


As mentioned earlier, the main panel is where the power comes into your property from the electric company. It usually comes with a main switch that allows you to connect and disconnect the supply.

It regulates and controls the power and, in several cases, the main panel also includes sub-main panels. Most of them have one main breaker, although they can have up to 6 breakers to control the sub-mains and other circuits. Many main panels also have a fused disconnector that can be pulled out.

A sub-main panel acts as a type of intermediary between the circuits that are part of the main panel and the property. They may include additional subpanels and connect directly via a special type of circuit feeder and also come with a breaker.

Sub-main panels are quite similar to the main panel. They, however, receive electricity from the main panel on the property instead of directly from the electricity provider, and are unable to push more power in an independent manner.

In summary, the main panel is where the power from the grid enters the property and the sub-main is what acts as a middle ground for the main panel and other circuits connected to the property.


The most common reasons why you would need sub-main panels are:

  • To act as a disconnect for large appliances or an outbuilding such as a garage or greenhouse,
  • If the main panel is full and you require additional room for circuit breakers.

When adding more sub-panels or circuit breakers, you need to keep in mind that it wouldn’t result in your home having more power. It is the main electric service and the wires coming into your main panel that determines how much electricity you will receive.

There are several advantages of having sub-main panels such as:

  • Separating the circuits so that your property can operate in the most efficient manner possible.
  • Easy identification of switches can help immensely during electrical maintenance and repairs.
  • Placing them anywhere, as opposed to main panels that are usually placed inside, and quickly turning them off in case of a fire or other emergency. This can prevent injuries and electrocution and help reduce the severity of the fire.
  • Adding extra circuits in case of limitations on the main panel.
  • Even distribution of power throughout the property without unnecessary burden on any one area.


If you do not have room on your main panel to install any additional breakers, or if you need a control point on a specific area, you can use sub-main panels which have 4 to 12 additional slots.

The first step to installing a sub-main panel is to determine its right size. To do so, you must consider a few things such as:

  • The sub-main’s required amperage
  • The additional demand on the main panel for which you need a sub-main.

You must make sure that the sub-main panel you choose has the adequate capacity to handle the required amperage. Its size, of course, has a lot to do with why you need it in the first place and the application that you need it for.

For powering light tools and equipment, a sub-main powering up to 6 amps should be enough. If you need more, you could get one that handles up to 100 amps.

To get the most out of the system, always pay close attention to the sub-main’s amperage and the power you plan on placing on the main panel.

The load calculation is another important aspect to consider since it specifies the total electric load that can safely run on a sub-main panel.

To calculate this, you need to know the type of devices you will run on the subpanel and the square footage of the area. These numbers will help you figure out the required amperage and the right-sized feeder cable.

Load calculation is part of the local electrical code and is used by electricians to get a better idea of the power supply and requirements. It includes the wattage of the electrical usage and the devices used on the sub-main panel.

The wattages are added together and the total is divided by 240. What you get is the capacity of the subpanel in terms of the amperage that it needs to have for installation.

Next, depending on whether the panel is installed indoors or outdoors, it needs to be designed to withstand the different environments.

If you want an indoor sub-main panel, you do not need it to be weather resistant. It will simply be installed by a certified electrician in a way that meets the local codes and regulations.

In the case of outdoor sub-main panels, they need to be weather-proof and resistant against all elements. For added protection, it is best to have a cover or shelter around the subpanel so that the sun, air, wind, and moisture do not interfere with its functionality.

It is always best to consult with a professional electrician who will be able to guide you better and ensure that the structure, wiring, and installation, all adhere to the current regulations.


The main function of a sub-main panel is to pass power from your electric company to a specific area on your property. Subpanels are basically mini main panels that help improve your electrical system and create more space on your main panel.

The total cost to install a sub-main depends on several factors such as its location, labour, and extra requests, and can fall anywhere from around £300 to £700.

If you look at it, you can actually save money in the long run by installing them as it means that you won’t have to run any wires underground and it will cost you much less when you decide to upgrade your main electrical panel.


There are several reasons why you would want to upgrade your sub-main, with the most obvious one being that it is too old and not up to the job anymore.

Other reasons include more power than what your sub-main currently allows or because you need to add new electrical systems.

The best way to determine whether you need to upgrade your sub-main (or main distribution board) is to check whether it is working fault-free and is compliant with the law, which is done through professional checks and inspections.

Periodic checks and inspections refer to having your electrical wiring, installations, and components checked by a professional and certified electrician who can give you a detailed report about each component and whether it is safe to use or not.

It is recommended in the wiring regulations BS 7671 that a domestic property must be regularly inspected and tested after every 5 to 10 years or if you are buying/selling the property.

For businesses and commercial properties, it is a requirement under The Electricity of Work Act 1989 to carry out an Electrical Installation Condition Report (EICR) at regular intervals, ranging from 3 to 5 years.

You may, of course, have the tests and inspections done more frequently as well, depending on your use and the health of your electrical system.


As part of the new 18th edition wiring regulations BS7671, it is now mandatory to incorporate surge protection in all domestic dwellings to prevent the damage of electrical installations and equipment.

What is surge protection? Surge protection is the use of a device, known as a surge protector, that is installed in line with a circuit to protect electronic devices and appliances in your home from surges in electrical power.

It works by channelling the excess voltage into the outlet’s grounding wire, preventing it from flowing through the electronic equipment’s circuits. While doing so, it allows the normal voltage to continue along its path to safely operate the appliance or equipment without causing it any damage.

In modern homes, there is extensive use of power-sensitive equipment such as computers, laptops, televisions, routers, refrigerators, washing machines, air conditioners, dishwashers, microwaves, CCTV cameras, and fire alarms.

Power surges can damage electrical equipment by ‘frying’ their internal components and causing permanent damage to them.

The inability to protect the above-mentioned appliances from power surges can account for thousands of pounds worth of damages. In addition to that, there is a serious risk of the equipment catching fire and putting you, your loved ones, and your property at risk.


We have been providing electrical services to residential, commercial, and industrial properties for over 40 years and are specialists in all aspects of electrical installations, maintenance, and testing.

We have experienced and fully qualified NICEIC registered electrical engineers on hand to deliver a professional and high-quality service.

If you have unplanned issues within your home or business, we can provide a call out service to rectify and solve any problems – ranging from circuits tripping, loss of power, broken items that need repairing, to distribution board and consumer unit upgrades, and much more.

Our team can generate a Visual Inspection Report (VIR) to identify anything visual that does not comply with the standards or looks unsafe, as well as a full Electrical Installation Condition Report (EICR) where we identify and test each circuit to make sure they are not deteriorating and are safe for use within the current standards and regulations set by the BS 7671.

We also provide PAT testing of appliances to make sure that any items such as kettles, computers, and microwaves are safe for use in the home and workplace.

Contact us here or call us on 0800 612 3001 to talk to our certified team of electricians right away!

Photo by Hamish Kale on Unsplash