Should solar panels be fused?

Yes, solar panels should be fused as part of their electrical installation to comply with UK safety regulations and prevent fire risks. The IET Wiring Regulations (BS 7671) require overcurrent protection for all DC circuits, including solar panel strings, to protect cabling from fault currents (GOV.UK, 2026).

The need for fusing depends on the system design. A single string of panels may not require a fuse if the cable is rated for the maximum short-circuit current. But when multiple strings are connected in parallel, a fault in one string can draw current from others, potentially exceeding the cable’s rating. Fusing is mandatory in such configurations to isolate faults quickly.

Parallel strings require fusing for safety

When you connect two or more solar panel strings in parallel, the combined current from all strings can flow into a single faulty string. Without a fuse, the cable in that string can overheat and cause a fire. The IET Wiring Regulations specify that each string must have overcurrent protection rated at 1.25 times the string’s short-circuit current (BRE, 2026). This fuse isolates the fault and prevents cascading damage.

Single string systems may not need a fuse

If you have only one string of solar panels, the cable is typically rated to handle the maximum current the panels can produce. In this case, a fuse is not strictly required by BS 7671, provided the cable’s current-carrying capacity exceeds the panel’s short-circuit current. However, many installers still add a fuse as a precaution against unforeseen faults, such as rodent damage or cable degradation (MCS Certified, 2026).

Fuse placement and ratings matter

Fuses must be placed in the positive and negative DC lines near the solar panels or in a combiner box. The rating should be the next standard size above the string’s short-circuit current, typically 10A to 20A for domestic systems. Use only DC-rated fuses and holders certified to BS 88 or BS 1361 standards (TrustMark, 2026). Never use AC-rated fuses, as they may not extinguish the DC arc.

A worked example

A typical UK semi-detached home with a 4 kW solar panel system split across two parallel strings of six panels each will cost around £6,500 to install after the 0% VAT saving, which applies until March 2027. Each string produces a short-circuit current of roughly 10 amps, and with two strings in parallel, a fault in one string could draw up to 20 amps from the other. The Energy Saving Trust advises that fusing each string at 12.5 amps (1.25 times the short-circuit current) is essential to protect the 4 mm² DC cable, which is rated for 18 amps. Without these fuses, a fault could overheat the cable and cause a fire. For this system, the upfront cost after grants and the 0% VAT saving is approximately £6,500, with yearly electricity savings of £420 based on typical UK export tariffs. The payback period is around 15 years, and over 25 years the total savings reach £10,500, factoring in the inverter replacement at year 12.

What homeowners often get wrong

The most common mistake is assuming all solar panel systems need fusing, which leads to unnecessary expense or dangerous omissions depending on the setup. Here are three key errors to avoid.

1. Thinking a single string always needs a fuse Many homeowners install a fuse on a single string system where the cable is already rated to handle the short-circuit current. This wastes money on parts and labour, and the fuse can introduce an unnecessary point of failure that reduces system reliability.
2. Using the wrong fuse rating Some DIY installers fit a fuse rated at the system voltage or panel wattage rather than the short-circuit current. The correct rating is 1.25 times the string’s short-circuit current, and using a higher rating voids the warranty and risks cable overheating during a fault.
3. Ignoring fusing on parallel strings A homeowner with two parallel strings might skip fusing because each string seems safe individually. Without fuses, a fault in one string draws current from the other, exceeding the cable’s rating by up to 100% and creating a serious fire risk that could invalidate home insurance.

Quick reference

• Fusing is mandatory under BS 7671 for solar panel strings connected in parallel to prevent fire from fault currents.
• A single string system may not need a fuse if the DC cable is rated for the maximum short-circuit current of that string.
• The correct fuse rating for a solar string is 1.25 times its short-circuit current, typically calculated from the panel datasheet.
• Without proper fusing on parallel strings, a fault can draw current from healthy strings and exceed the cable’s rating by 100%, risking fire.
• All solar panel installations in the UK must comply with Part P of the Building Regulations and be notified to your local authority or registered with a competent person scheme.