Ask an experienced AC electrician to wire a solar array and, without specific training, they will do several things that are perfectly correct on the AC side and dangerous on the DC side. This is not carelessness. It is a genuine discontinuity in the physics, and it deserves to be understood rather than memorised.
The zero crossing
When an AC circuit is broken under load, an arc may strike — but alternating current passes through zero twice per cycle, and at each crossing the arc has a natural opportunity to extinguish. Switchgear is designed around this generosity. Direct current offers no such thing. The current is continuous, so a DC arc, once struck, has no reason to stop. It will sustain itself across a widening gap and burn until something interrupts the circuit or the fuel runs out.
This is why DC isolators are a different component, not a re-badged AC switch, and why pulling a live DC connector is never a shortcut.
An array is never off
The second uncomfortable fact: you cannot switch a module off. In daylight it is generating, full stop. Isolating the inverter does not de-energise the DC side; it just leaves live conductors up on the roof with nowhere to go. Work is planned around that reality — isolate correctly, verify rather than assume, and treat every string as live because it is.
Where it actually goes wrong
Most of the DC faults we find on inspection are not exotic. They are connectors crimped with the wrong die, so the joint has a slightly high resistance that heats, oxidises, heats further and eventually arcs. They are mismatched connector brands mated together because they physically click. They are undersized or absent string protection. Each is trivial to do correctly on the day and expensive to discover later — usually as a burn mark.
- DC arcs do not self-extinguish — there is no zero crossing to help you
- DC isolators are purpose-built; an AC switch is not a substitute
- A module in daylight is always live; isolating the inverter changes nothing on the roof
- Crimp with the correct die, and never mate mismatched connector brands
- Verify isolation by measurement, not by assumption
None of this is a reason for alarm about solar, which is a mature and remarkably safe technology when installed by someone who understands it. It is a reason to care a great deal about who installs it.
Written by Engineering team. This article is general guidance, not a substitute for a site-specific assessment.