Updated
Burning Smell Or Scorching At The Solar Isolator
A hot, acrid smell near the inverter, browning around a switch, or an isolator that is warm to the near touch.
Find a solar installer
What's happening?
This is the failure mode that turns a solar system into a fire, and it has a specific cause worth understanding. The DC side of an array runs at high voltage whenever there is daylight, and unlike alternating current it does not pass through zero volts many times a second — so when a connection loosens or corrodes, the arc that forms across the gap sustains itself instead of self-extinguishing. That arc generates heat inside an enclosure nobody looks at. The two usual locations are rooftop DC isolators, whose enclosures have a long history of water ingress on UK roofs, and DC connectors that were crimped badly or were mismatched brands at installation. The warning signs are the ones this page is named after: smell, browning of plastic, heat, or a buzzing or crackling that was not there before. Unlike almost everything else in solar, this one is urgent.
What usually causes it?
- Water ingress into a rooftop DC isolator enclosure, corroding the contacts
- DC connectors of different makes mated together, giving a poor and worsening contact
- A badly crimped connector from the original installation, degrading over years of thermal cycling
- Terminals that were never torqued correctly, loosening as the array heats and cools daily
- Rodent damage to DC cabling in a loft or under the array
- An inverter mounted with no ventilation, running hot enough to age its terminations
Is it dangerous?
Yes, and this is the one page in this category where the answer is act now. A burning smell, visible scorching, melted plastic or crackling at any part of a solar installation is a live fire risk. Switch off the AC isolator for the solar system if you can reach it safely. Do not open the inverter, the isolator or any DC enclosure. Do not touch or pull DC connectors — the DC side stays live in daylight no matter what you switch off indoors. If there is smoke, visible flame or heat you can feel through a wall or ceiling, leave and call 999.
Can I fix it myself?
Nothing beyond making yourself safe and switching off the AC side. This is not a reset, a clean or a tighten. The DC circuit cannot be made dead by a homeowner because the panels generate whenever light falls on them, which is exactly why loose DC connections are so dangerous — the energy keeps arriving while the fault develops. Record what you saw and smelled, then get an installer out the same day.
When should you call a solar installer?
Same day, for any burning smell, scorching, discolouration, melting, buzzing or crackling anywhere in the system. Same day too for a warm isolator enclosure or an inverter that has become noticeably hotter than it used to be. Where there is any doubt about fire, the fire service first and the installer afterwards.
What will the solar installer actually do?
- Isolate the system safely, working on the basis that the DC side remains live in daylight
- Open and inspect isolator enclosures and connectors for arcing damage, corrosion and water
- Thermally survey terminations and connectors under load to find developing hot spots
- Replace damaged isolators, connectors and cable, using matched components rather than mixed makes
- Check the inverter's terminations, ventilation and mounting position
- Re-test the strings and insulation resistance before returning the system to service
Frequently asked questions
We’re happy to answer all your questions.
Need a solar installer?
Compare local solar installers on Tradehand — coverage areas, accreditations and phone numbers, no middleman.