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DC isolators cop flak as ‘PV fire risk’ story spreads

May 01, 2023

Rooftop solar isn't perfect. Performance can be affected, not surprisingly, by hailstones the size of tennis balls, temperature extremes and Old Man Time. Poor-quality equipment and shoddy installation work will also compromise output. But it never helps when the media weighs in with stories about systems catching fire and pins the blame on DC isolators.

"Over the last five years we have seen solar panel-related fires increase five-fold," Fire and Rescue NSW manager fire investigation and research Graham Kingsland told regional media last year. "It is not uncommon to see solar panels cause house and building fires."

Kingsland's comments followed a bad week for PV in NSW. In November last year, solar panels were found to be the cause of five fires in the state: four that started in isolator switches and one in a fuse box. The agency reported fire incidents related to solar panels were up by more than 20% compared with late 2019, "with solar isolation switches causing almost half of all solar panel-related fires".

Between December 1, 2020, and January 12, 2021, Fire and Rescue NSW responded to about 15 fires across the state related to solar panels.

It is true that an incorrectly or badly installed DC isolator is a fire risk. It's a stretch to say fires caused by solar panels are "common". Statistics from the Australasian Fire and Emergency Service Authorities Council show faulty solar systems caused 400 residential fires in the seven year 2009 to 2015 (the most recent statistics available), or about 1.5% of all reported fires.

When attached to a string system, a DC isolator must manage a high current and voltage. If a DC isolator is faulty, water has entered it or cabling is loose, there will be a chance of arcing, which creates heat that can lead to smoke and sometimes fire. Many such fires are contained to the boxes, but they can spread.

"DC won't trip a circuit breaker or blow a fuse; it will burn until it separates," says Clean Energy Council technical team lead installation integrity Robbie Nichols.

Rooftop DC isolators are mandated in Australian Standard 5033, which sets down the safety and installation requirements for PV systems. (Although the standards are shared with New Zealand, the industry there successfully called for the removal of the clause on DC isolators.)

The CEC's guidelines around DC isolators, which have been refined since they were introduced around 2012, stipulate the use of multi-hole glands to prevent water ingress and no top entry points.

Some DC isolators may have been in service for nearly a decade, however, and anything exposed to the elements that long will have taken a beating. Plastic housings may be prone to corrosion and seals could be cracked or warped, allowing for water to enter. It's a maintenance issue that affects older systems, Nichols says, as current installation practices have done much to reduce the chances of failure.

Nonetheless, the CEC is leading a re-write of the Australian Standard that deals with the installation of rooftop DC isolators. The committee working on the re-write includes state and territory electrical safety regulators, fire safety and emergency services, peak industry bodies and product manufactures.

A spokesperson for the CEC said, "We are not against the removal of rooftop DC isolators, but we do want to see the safest and most practical solution implemented." The most recent data from the CEC shows 1.7% of PV systems inspected are being classified as unsafe.

Enphase, whose technology includes microinverters and relies on AC isolators, has released a report that underlines the threat of fire risk in DC isolators. Some media pieces have linked to the Enphase report. There is no risk of DC arcing with AC isolators.

If some are claiming that DC systems are unsafe, SolarQuotes founder Finn Peacock disagrees. "A properly installed DC system is perfectly safe," he tells EcoGeneration.

Peacock says the problem is that the rooftop units take a beating from the weather, simple as that, and metal shrouds stipulated over the past few years to protect the boxes is a good move. "The DC isolators that were on the roof before the shrouds came into force should probably all be inspected and retrofitted," says Peacock (pictured above). "If water gets into a DC isolator it's bad news. High-voltage DC arcs so easily."

Installers have a hectic time running from one job to the next but their sales pitch to customers should include an offer of a paid service check a few years down the track. "I think systems should be inspected every five years," Peacock says. "The problem is, I suspect 95% of systems don't get inspected every five years … even though it's mandated in some of the DNSP areas."

A catch-up with old customers is a great opportunity to talk about adding a battery, upgrading a water heater or upsizing the PV system, he says. "If you got a solar system five years ago it's probably too small."

Perhaps the last word on the subject should go to Kingsland from Fire & Rescue NSW. "By ensuring solar panels are installed by a licensed installer, and are well maintained by a professional, you can prevent a tragedy."

Every solar installer would agree with that.

Where there's smoke Book a check-up