The correct size of the fuse to be fitted in the connection unit for your 1 kW lighting circuit in the UK would be a 5A fuse.
Fused spurs are typically used to supply power to appliances or lighting circuits, and the correct size of the fuse to be fitted in the connection unit depends on the rating of the circuit and the load it's supplying. In your case, you have a 1 kW lighting circuit
Here are the step-by-step instructions to determine the correct size of the fuse for your 1 kW lighting circuit:
1. Determine the load rating: You've already mentioned that you have a 1 kW lighting circuit. 1 kW is equivalent to 1000 watts (since 1 kW = 1000 watts)
2. Convert the load to amperes (A): To calculate the current (in amperes) for a circuit, you can use the formula:
Current (A) = Power (W) / Voltage (V)
In most residential settings, the voltage is 230V (in the UK) or 120V (in the US). However, make sure to use the correct voltage for your location.
For example, if you're in the UK with 230V:
Current (A) = 1000 W / 230 V ≈ 4.35 A
3. Choose the appropriate fuse rating: In the UK, common fuse ratings for lighting circuits are 3A or 5A. In the US, common ratings are 15A or 20A. Since your calculated current is approximately 4.35 A (in the UK), a 5A fuse would be suitable.