A sudden increase in electrical current isn’t a rare event. Whether through manufacturing errors, wire age, or natural forces like storms, electrical current is rarely stable all the time. So, how are you protected from this potentially dangerous fluctuation in energy?
Fuses – and by extension their ratings – determine how much current can be channelled through an appliance or fitting. This safety measure protects the appliance or fitting from damage and people from harm.
So, what is a fuse rating? How does a fuse work, and how is a rating calculated? Below, we discuss all you need to know about fuse ratings, including the role fuse rating labels have.
What Is a Fuse, And How Does It Work?
A fuse is a tiny electrical safety device that helps to prevent overcurrent in an electrical circuit.
Placed within the circuit, its metal wire or strip melts when too much current passes through it. This breaks the circuit and interrupts the flow of electricity,
What Is the Difference Between a Fuse and a Circuit Breaker?
Both fuses and circuit breakers work in a similar way – they both break electrical circuits when there is a surge of energy. However, a circuit breaker is a switch that can be reset once it has been flipped. Once a fuse has ‘blown’ it cannot be reused, so a replacement must be fitted.
Types of Fuses and Circuit Breakers
Fuses are used in all kinds of applications, everywhere from your kitchen kettle to the engine of your car. Therefore, there are numerous different types of fuses which vary in size, current and voltage ratings, as well as breaking capacity and response times. Regulations outline the maximum current and fuse rating that is allowed per application.
The three main fuse speeds are:
• Ultra-rapid
• Fast acting
• Slow acting
Let’s take household fuse ratings as an example. When it comes to circuit breakers, you may have an older consumer unit fitted with a semi-enclosed, rewirable fuse or cartridge fuses. More modern homes will likely have miniature circuit breakers instead of fuses. Generally, these will allow 5 amps for lighting circuits, 15 amps for heating, and 20 amps for small radial circuits.
A British Standard plug will have a 3 amp or 13 amp fuse. The lower will be used for running smaller devices such as kettles, toasters, or a TV, whereas the larger for ovens, washing machines, and so on.
What is a Fuse Rating?
When a circuit overloads, the following happens:
1. The wire fuse element heats up quickly.
2. The fuse then melts or explodes, depending on the current.
3. The broken fuse interrupts the flow of electricity.
The conditions for this to happen are dependent on the fuse rating. The fuse rating relates to the strength of current allowed through the circuit, which changes depending on the type of application. The more potentially dangerous an appliance is, the lower the fuse rating will be.
What Is the Difference Between an Interrupting and Ampere Fuse Rating?
An ampere rating is the minimum amount of current needed for an appliance to operate.
An interrupting rating indicates the maximum energy a device can safely handle. This is the sacrificial rating that maintains safety.
How to Find a Fuse Rating?
In the UK, all fuses must be labelled with the correct fuse rating. These are usually written on the body of the fuse itself and are colour-coded:
• 1 amp – black
• 2 amp – grey
• 3 amp – violet
• 4 amp – pink
• 5 amp – beige
• 7.5 amp – brown
• 10 amp – red
• 15 amp – blue
• 20 amp – yellow
• 25 amp – clear
• 30 amp – green
• 40 amp - amber
As most appliance fuses are housed within a 3-pin plug, you’ll find this maximum power rating on the underside of the plug also.
It’s very important that electrical suppliers both test and label the efficacy of their fuses. If a fuse isn’t labelled correctly, then electricians and other maintenance staff may be in danger as they won’t know what they’re working with.
Without fuses, the risk of electrical injuries and fires would increase tenfold and the health and safety surrounding them would be even more stringent.
How to Calculate a Fuse Rating
Fuse rating calculations need to be exact. So, if this is not immediately clear, it is good to know the fuse rating formula so you can calculate this yourself. Alternatively, a fuse rating chart could help.
To calculate a fuse rating, manufacturers work from a simple equation:
Power (watts) = Voltage x Current (amps)
What we really want to know with this equation is the current (amps). So, using this equation as a basis, the fuse rating can then be calculated with the following:
Amps = Watts / Voltage
So, let’s say we need to work out the fuse rating for a washing machine. It uses 850W of energy at 120V. So, the equation would be:
850/120 = 7.08 amps
This means the washing machine, at maximum energy, would use 7.08 amps of power. So, a 10 Amp fuse would suffice, as that is well over 7.08 amps it produces.
Get Fuse Rating Labels Today
As mentioned previously, calculating fuse ratings alone isn’t enough – you need to label them correctly too.
At Label Source, we stock a range of high-quality fuse rating labels for different ratings. We also supply other electrical identifiers such as earth symbol labels, which may be of interest. Take a look and please get in touch if you have any questions.
