Solar wiring and protection
The dangerous mistake is to treat the roof cable like a household wire. Direct current does not pass through zero the way alternating current does, so a poor connector can sustain an arc. Protection is designed. It is not a list of breaker ratings on this page.
Two sides of the system
DC cabling
Solar cable is built for outdoor ultraviolet light, heat, and the voltage of the string. Ordinary house wire is not a substitute on the roof.
AC cabling
From the inverter to the distribution board the current is alternating. That run follows the AC design: size, protection, and the route into the existing board.
Why the difference matters
DC faults are harder to interrupt. AC protection devices are not automatically correct on the DC side, and the reverse is also true.
Devices you will hear named
MC4 connectors
The usual locked connector between modules. They must be the mating type the design calls for, clicked fully, and not left open in the rain. Do not cut them off to twist wires together.
DCDB and ACDB
The DC distribution board gathers the strings, isolation, and DC protection. The AC distribution board sits on the inverter output. They are not decorative boxes.
MCB and MCCB
A miniature circuit breaker protects smaller AC circuits. A moulded-case breaker is used where the current or the fault level needs it. The choice is calculated.
SPD
A surge protective device gives a lightning-related or switching surge a path away from the inverter. It has a life. A window or flag that says it has failed means it needs replacement, not tape.
Isolators
An isolator lets a qualified person make the circuit visibly or mechanically open before work. It is not a switch to play with while the array is live.
Size, drop, and route
Cable size depends on the current, the length, how the cable is installed, and how much voltage you can afford to lose on the way. A long thin DC run wastes power and can sit outside the inverter's tracking window. This page does not publish a square-millimetre for every roof.
Routes stay out of standing water, away from sharp edges, and clipped so the wind cannot fret them. Loops of spare cable on a hot terrace are a future crack, not a sign of generosity.
Connector safety
Do not open an MC4 while the string is producing current. Do not use two different connector brands as a pair unless the manufacturer says they mate. A half-clicked connector is a heat fault waiting for a sunny afternoon.
Common mistakes
House wire on the roof
It is not rated for the sun and the string voltage.
One breaker for both sides
DC and AC protection are specified separately.
Bypassing a device that trips
A trip is information. Bridging it removes the protection and can start a fire.
Where to read further
Wiring questions
What cable size do I need?
It is calculated from current, length, and installation. There is no single size on this page.
Can I use an AC breaker on the solar strings?
Not as a substitute. DC interruption is a different duty. The DCDB is specified for that duty.
Are MC4 connectors safe to unplug?
Only after the string is isolated by a qualified person. Unplugging under load can draw an arc.
Related guides
- Solar panel technologyCells, module types, efficiency, heat, degradation, and why DCR matters for the central scheme.
- Solar inverter guideThe inverter turns panel current into household current and decides what happens when the grid fails.
- Solar structure and mountingThe structure holds the modules to the roof. Its size is an engineering result, not a catalogue guess.
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