[scrumper]

The failure here wasn't overcurrent, which is what fuses (or breakers) mitigate. Here it was poor connection, no fuse or breaker would help. And in fact didn't since the author mentioned he had breakers on these lines.

Also, and particularly in high current circuits like these, fuses generate significant heat on their own, at the connection points.

The better bet is to look to conservative standards (like ABYC for the marine industry) and follow their rules for wire termination. In this case that would be properly crimped ring terminals over simply wrapping stranded cable around a screw. That said I am sure the NEC has something to say about domestic solar installations.

[1970-01-01]

The idea is your inline fuse overheats and melts instead of the entire controller turning into fire due to the heat cooking the plastic at the rail or terminal. It's a passive device for both overcurrent and overheating. Or just step into 2026 and use mag breakers, there are lots of DC breakers that do this: https://www.amazon.com/Miniature-Circuit-Isolator-Magnetic-D...

[BenjiWiebe]

The issue wasn't heat generated by excessive current, but heat generated by excessive resistance and normal current.

Mag breakers and fuses won't help. A thermal fuse could work,provided it was thermally bonded to the bad connection. So you'll need a lot of thermal fuses - one at every potential bad connection.

[1970-01-01]

Mag breaker opening under overtemp condition:

https://www.youtube.com/shorts/thUbyzO8Cek

[theamk]

This only happens when there is an overcurrent condition. As OP, scrumper, BenjiWiebe all told you there was no overcurrent condition. The system was rated for a 100 amp, the current was under that.

The thermal overload breaker won't help here, because it only trips when the current is above breaker rating. And one would install at least a 100A breaker into a circuit rated for 100A, or it'll just trip all the time.

(You can see the detailed curve on datasheet, example page 2 here [0]. It is surprisingly slow - for 1.5X overload, it takes >10 minutes to trip).

The problem was because of bad connection on 100A line. We can talk about mistakes made here, but lack of breaker was not one of them.

[0] https://www.eaton.com/content/dam/eaton/products/electrical-...

[1970-01-01]

>This only happens when there is an overcurrent condition.

It happens when it gets too hot. Principle of Operation: The Bimetallic Strip Mechanism:

https://www.haipart.com/news/thermal-trip-unit-in-circuit-br...

[theamk]

have you actually read this page?

> If the current exceeds the rated load for a prolonged period, the heat causes the bimetallic strip to bend.

> The unit trips after a delay inversely related to the magnitude of the overload; the greater the current, the faster the trip.

The heat is generated by the breaker itself, from the current. Maybe it'll trip slightly faster if the wire is very hot, but I say it's unlikely - the thermal resistance on a regular breaker is very low, and wire is not a very great heat conductor either.

And even if breaker was for some reason reacting on wire temperqture? Look at the original post. You can easily see how far the heat traveled simply by seeing where the insulation got blackened. It looks like just a few cm - nowhere close to get to the other end of the wire, which was in the breaker. The system had breaker, and it could not detect this condition.

(There are special "thermal fuses" which react on the external temperature, but they are very distinct from the regular circuit breaker, and they must be attached directly to the device emitting heat, like a motor. No one attaches those to the regular terminal strips)

[BenjiWiebe]

Also, btw, the 'mag' part of the breaker is irrelevant. The magnetic component is for sudden large overcurrent events, to provide a quicker break than what a bimetallic strip can do.