Are isolators on the roof unreliable?

YES.

15 years ago we didn't have to install isolation points on the roof for solar power systems, but there were a lot of things we didn't have to do, and standards have thankfully improved a lot since then.

However one of the standards changes introduced switch disconnect rooftop isolators.

These RTIs are the most unreliable part of solar systems. Blokes in the industry refer to them as rooftop incendiaries. Stupid as it sounds they were often just installed backwards, and despite standards changes to how they were specified, fixed, mounted, wired and even sheltered with metal shades, the newest update to AS5033:2021 actually means we have convinced the authorities that they're a bad idea, so we no longer use them in most instances.


Faded cables, faded labels, failed sealant, no gland fitting, isolator screwed direct to the panel frame, poor workmanship generally.

The solar industry has had a love/hate relationship with firefighting for a long time now. For many years we have had to install isolators on the roof attached or adjacent the arrays. We were told that this was because "the fireys wanted to switch them off" which was an interesting furphy because the fire service won't climb on the roof of a burning building in any case.

Metal shade rendered useless by poor installation

It took a long time for them to be written out of AS5033 but finally the rule makers have seen some sense.

If a building has been burnt out (but not collapsed) and all the wreckage is blackened inside, it's right enough that the emergency services want the place rendered safe from burnt but still live wiring. So now instead of a switch disconnect or RTI which "anyone" can operate, a solar array can be made safe by appropriately qualified people using a simple tool to unplug, and thus isolate the solar... like it was 15 years ago, except now we also have better wiring standards for how the cables are run inside the building.

Isolator hidden under a panel, which means it's best protected but maddeningly this is against the rules. In any case there is a gland missing so this isolator is open to water, insects & lizards.

If your system is more than 5 years old I strongly suggest it's worth getting this item checked for peace of mind. They often get full of water and fail, bursting into flames and causing fires even if they were reasonably well installed. Get someone else qualified in solar to do an inspection and be prepared to have a metal shade installed if yours is an old system that doesn't have one.

This was an isolator...

So things are looking up, the roof top incendiaries are becoming a thing of the past, but be aware that if your system has a failed isolator, repairs might mean the whole DC cable run from the roof to the inverter needs to be replaced, in order to meet the current standards, and delete the RTI.

If the wiring is ok or it's too hard to replace because of a complex run, a new isolator assembly with weather shade, new conduit, gland fittings and condensation drain valve may be the best approach.