5

I am installing a solar panel which requires a 7m cable run.

All the diagrams I've seen on the internet suggest fusing at the charge controller end. This protects against charge controller failures, but what about a mid wire short on a sunny day.

I appreciate that there is nothing wrong with fusing the +Ve at both ends of the wire, but why isn't this recommended?

3

Explaining what John says in a slightly different way:

The current that a PV (solar) panel produces in full sunlight at its maximum power point is termed Imp.

The current that a PV (solar) panel produces in full sunlight when short circuited is termed Isc.

The increase in current from Imp to Isc is typically about 10%. eg if a panel makes maximum power when current = 10A, then shorting the panel into a zero Ohm load will produce about 10 + 10% = 11A.
The increase from Imp to Isc is so small that there is no difference hazard wise. For example, if a wiring run droppeed 1 Volt at 10A then the power lost would be P = I x V = 10 x 1 = 10 Watt.
At 11A the voltage drop would be 1.1 Volt and the power lost would be
I x V = 11 x 1.1 = 12.1 Watt. The extra 21% loss of 2.1 Watts would be spread over many metres of cable and would make no noticeable difference to heating - or any other aspect.

So - fusing at the panel end is not needed as I_short_circuit is hardly more than I_maximum_operating.

5

There is no benefit to having an extra fuse at the solar panel. The fuse at the charge controller end is recommended (an in some jurisdictions a requirement).

From https://www.boats.com/how-to/solar-panels-what-about-fuses-or-breakers/

Solar panels are what are known as “self-limiting” devices, meaning that no matter what, the amount of amperage they can produce is limited. A breaker or fuse would never trip in the event of a short circuit between the panels and your charge controller. Remember that what blows fuses and trips circuit breakers is amperage that is excessive for the circuit in question.

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