Circuit Protection Buying Guide

Fuses are a type of single-use circuit breaker, often found in household appliance plugs – once blown, they must be replaced. They’re small devices with a thin metal strip inside called a resistor – made of tinned copper – which melts when there’s a fault. You’ll find 3 amp, 5 amp and 13 amp fuses which must be compatible with the current for your device. Generally, appliances up to 700W use 3A fuses, while 13A fuses are for 700W appliances and greater. A fuse speed rating tells you how fast the fuse will blow in the event of a fault – the faster the speed, the safer the fuse. A voltage drop rating indicates how much voltage is absorbed into the fuse – the higher the amp, the greater the voltage drop.

Fuses are effective and inexpensive, and can be replaced quickly and easily, including by a DIYer with little electrical knowledge. Simply choose the same fuse that was already in the plug. Fuses are colour-coded for easier identification – pink for 3A, brown for 13A, and black for 5A.

The main consideration with a fuse is that they’re only suitable for use with appliances that are plugged in, rather than hardwired in.

RCCBs are residual current circuit breakers, and are found in consumer units. They mainly protect against electric shocks and fires by measuring the outgoing current against the incoming current. If the current is different, there is ‘earth leakage’ which means some electricity is being lost somewhere and potentially causing – or could cause – an electric shock. RCCBs have a range of amp ratings, phases and curve types suited to different uses.

RCCBs, unlike MCBs, are specifically designed to protect users from electric shock. For this reason, RCCBs are a valuable component of a consumer unit and shouldn’t be forgotten in residential or commercial applications. Also, RCCBs can protect up to 5 circuits with one device.

However, RCCBs cannot protect against overloading or short-circuiting on their own – they need an MCB to assist, or should be replaced with an RCBO.

Miniature circuit breakers, also known as MCBs, are designed to prevent damage caused by a short-circuit or overloading current, and are commonly found in consumer units. Similar to fuses, a metallic strip deflects when the current is too high which releases a latch that stops the current flow. Different MCB types trip at different rates – type B when the overload is 3-to-5 times its load current, type C between 5-to-10 times its load current, and type D between 10-and-20 times its load current. Type D is better suited for industrial use where there are high inductive loads. 

There are also a range of amp ratings which make MCBs perfect for different situations. 6A to 50A MCBs are used in domestic environments, while higher amp ratings are better for commercial and industrial electrical circuits. 

The main consideration with MCBs is that they do not protect against earth faults – where a conductor comes in contact with the earth and could be causing an electric shock. They are best used alongside RCDs which can offer this protection.

RCBOs are a type of device found in a consumer unit that keeps an eye on current going around the circuit to provide protection against electric shock, and also protect an appliance from overload. Essentially, they combine the benefits of MCBs and RCCBs. They can trip when there is an imbalance of current going in and out of the circuit to protect against electric shock, and a metallic strip will deflect in the case of an overload or short-circuit to protect the appliance.

Similar to RCCBs, there are a range of amp ratings and types to choose from so RCBOs can be compatible for a range of circuits and applications. However, unlike RCCBs, they’re used for just one circuit, meaning they won’t cut the power to a larger number of appliances when just one has an issue.

However, RCBOs have a higher price tag than RCCBs and MCBs and you’ll need a separate device for every circuit you wish to protect in this way.

Isolator switches are used to isolate one section of a circuit in case of repairs, servicing and maintenance. They are usually used if there is a higher risk of electric shock, such as in high voltage circuits, and can be used alongside circuit breakers as a second layer of protection from electric shocks when carrying out maintenance. Isolator switches can be found in a range of environments from domestic properties for electric showers, extractor fans and air conditioners, to industrial power grids.

The main advantage of an isolator switch is that they provide an extra level of protection against electric shocks. They also allow you to cut power to only one small section rather than the entire circuit which can reduce downtime.

Isolator switches, whilst beneficial, are an extra cost to consider when setting up or altering an electrical circuit.

Surge protectors, also known as SPDs, are devices that protect equipment from voltage spikes – caused by electrical faults or lightning strikes – which can damage appliances. You’ll find surge protectors available on their own or already built into an appliance or power distribution board. They work by blocking or diverting excess power to the ground when the voltage increases beyond safe levels. 

You’ll find surge protectors fitted with warning lights which can let you know if there is a problem, as well as indicate that they’re working correctly. 

The main consideration with surge protectors is that they may have voltage limitations and wont work correctly if the voltage is too high. You should also consider how often power surges occur or are likely to occur, as this means you might need a more powerful model.