In electrical installations, both fused spurs (also known as fused connection units or FCUs) and 20 amp switches serve specific purposes—but they are not interchangeable. Choosing the correct device is crucial for both safety and functionality, particularly when connecting fixed appliances such as extractor fans, heating units, lighting circuits, or underfloor heating.
This article explains the key differences between the two and highlights why a fused spur is often the better option.
A fused spur is a hard-wired connection point that includes a built-in fuse, typically rated at 3A or 13A. It’s designed to:
Safely isolate an appliance
Provide overcurrent protection to a specific part of the circuit
Be used with fixed equipment not requiring a plug-and-socket connection
A 20 amp double pole switch is generally used as an isolation switch, often found on lighting circuits or immersion heaters. It:
Does not have built-in fusing
Can isolate both live and neutral conductors
Typically requires the circuit to already have adequate protection via the consumer unit
Many fixed appliances (e.g. extractor fans, underfloor heating thermostats, LED drivers) require a fuse with a lower rating than the circuit breaker supplying the circuit.
A 32A ring final circuit may feed multiple fused spurs, each protecting appliances with their own 3A or 5A fuse.
A 20A switch offers no such protection, relying solely on the upstream breaker, which may be too high for the appliance.
Most appliance manufacturers specify a fused spur in their instructions, especially for:
Bathroom fans
Boilers
Integrated kitchen appliances Using a 20A switch may invalidate the warranty or fail to meet BS7671 wiring regulations.
Fused spurs come in compact formats, available as:
Switched or unswitched
With neon indicators or no indicators They’re ideal for discreet placement under counters, in airing cupboards, or near control units.
A switched fused spur provides both isolation and protection, meaning:
You can safely disconnect the appliance during maintenance
It provides an easy reset method in the event of a fuse blow
Fused spurs are often used on lighting control accessories like:
PIR sensors
Lighting control modules
Smart relays
This allows those low-power devices to be fused independently, reducing the risk of overload or damage.
A 20A double pole switch is suitable when:
The appliance has its own internal fuse (e.g., some immersion heaters)
The circuit has dedicated protection at the consumer unit (correct MCB rating)
You need a clearly visible isolation point (e.g., cooker switch with a socket)
| Feature | Fused Spur | 20A Switch |
|---|---|---|
| Built-in Fuse | ✅ Yes (3A, 5A, 13A options) | ❌ No |
| Overcurrent Protection | ✅ Yes | ❌ No |
| Suitable for Appliance Loads | ✅ Yes | ⚠️ Sometimes, if internally fused |
| Isolation Function | ✅ Switched models | ✅ Yes (double pole) |
| Space Saving Design | ✅ Compact | ❌ Typically larger |
| Compliant with Manufacturer Requirements | ✅ Often required | ❌ May void warranty |
If you're connecting a fixed appliance that doesn’t have its own fuse—or where manufacturer's instructions specify protection—a fused spur is the safest and most compliant option. While 20A switches have their place, they are not a substitute for fused protection and are best used only where appropriate.
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