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Your home’s electrical supply fuse is one of the most important safety components in the entire property. It protects your main incoming supply by disconnecting the electricity if a fault or overload occurs. Despite being a small device, the supply fuse plays a critical role in preventing electrical fires, equipment damage, and dangerous overheating.

In this guide, we’ll explain what domestic supply fuses are, the common sizes you’ll find, what they protect, and when you might need an upgrade.

What Is the Main Supply Fuse?
The main supply fuse—sometimes called the service fuse, cut-out fuse, or main protective device—is the fuse fitted by the electricity network operator where the mains supply enters your property.
It is typically located:
-Inside the cut-out or service head
-Next to the electricity meter
-Before the consumer unit (fuse board)
Unlike the fuses and breakers inside your consumer unit, the supply fuse cannot be reset by a homeowner and must only be worked on by authorised personnel.

What Is the Purpose of the Supply Fuse?
The supply fuse has two crucial jobs:
1. Protect Against Overloads
If too much current is drawn through the incoming supply, the fuse melts and disconnects the property. This prevents:
-Cable overheating
-Fire risks
-Damage to appliances
2. Provide Short-Circuit Protection
If a major fault occurs—such as a live-to-neutral short—the fuse cuts power instantly to stop the fault escalating.
Because it’s the very first protective device in your installation, its rating must be appropriate for the capacity of your home.

Common Domestic Supply Fuse Sizes
Domestic properties are typically supplied using one of the following fuse ratings:
60 Amp Supply Fuse
-Common in older properties
-Suitable for small homes with fewer high-load appliances
-May struggle with: Electric showers, EV chargers, induction hobs, heat pumps
80 Amp Supply Fuse
-Mid-range capacity
-Adequate for most modern homes
-Supports moderate electric heating loads
100 Amp Supply Fuse
-Most common in newer installations
-Suitable for larger houses or high-demand homes
-Often required when installing EV chargers, heat pumps, or multiple electric showers

How Much Power Do These Fuse Ratings Provide?
To estimate the power capacity:
Power (kW) ≈ Voltage × Current ÷ 1000
For a 230V supply:
-60A → ~13.8 kW
-80A → ~18.4 kW
-100A → ~23 kW
This doesn’t mean you can run that much power continuously, but it gives an idea of the overall supply capability.

Signs That Your Home May Need a Supply Fuse Upgrade
You may need a higher-rated supply fuse if you’re:
-Adding an EV charger
-Installing a large electric shower
-Upgrading to electric heating or heat pumps
-Adding air conditioning
-Installing a hot tub or sauna
-Expanding your home (extensions or loft conversions)
-Frequently experiencing tripping due to high load demand (though this may be a consumer unit issue)
A qualified electrician will calculate your maximum demand and advise whether your existing fuse is sufficient.

Who Is Allowed to Change a Supply Fuse?
The main supply fuse belongs to the electricity network operator, not the homeowner. Only authorised engineers are legally permitted to:
-Remove the fuse
-Replace the fuse
-Increase the supply rating
Electricians cannot upgrade the supply fuse themselves, but they can carry out load assessments and arrange the upgrade with the network operator on your behalf.

What Happens During a Supply Fuse Upgrade?
Upgrading the supply fuse often involves:
-A load assessment to check if the home requires a higher rating
-Inspection of the incoming cables (service cables must be capable of handling the higher current)
-Possible meter/bonding upgrades to meet safety standards
-The fuse being replaced with a higher-rated one (e.g., 60A → 100A)
In many regions, the network operator will complete the upgrade free of charge or for a small fee, depending on cable capacity.

Can You Run Into Problems With an Undersized Supply Fuse?
Yes. An undersized main fuse can lead to:
-Frequent nuisance blowing (rare but possible)
-Inability to install new high-load appliances
-Overloaded Supply Tails
-Lower efficiency due to load restrictions
It may also prevent future electrification upgrades—especially as homes increasingly move toward electric heating and vehicles.

Final Thoughts
Domestic electrical supply fuse sizes are an essential part of your home’s electrical safety. Whether you have a 60A, 80A, or 100A fuse, its rating determines how much load your property can safely handle and whether it’s ready for modern electrical demands.
If you're planning electrical upgrades—especially high-power appliances—it's always best to have a professional assess your maximum demand and advise whether a supply upgrade is necessary.

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08/12/2025

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