Circuit Breaker End of Life

[SailingHarmonie]

As my boat gets closer to her 30th birthday than her 20th, I have had a significant number of breakers (~10%) fail. In every case they began to trip significantly below rated current, well down into the normal operating range.

Now, sort of failing open, and stying open, this is the best possible failure mode, because I can see it happen, although the first time took me a while to figure out, since breaker failures like this were not very high up on my "likely failure " list when troubleshooting an electrical fault. That's changed

It does leave me with a nagging question however...

Suppose a breaker failed the OTHER way? i.e., Not tripping when it was supposed to. Short of corroding into a solid lump, does that ever happen? Short of replacing all breakers as a preventative measure, is there a way to detect sure a failure?

[capt jgw]

Breakers don't last forever, they do wear out. They're designed to fail safely just as you've described. But corrosion, maybe that could cause them to "stick" closed and not trip when they should. I'm thinking not because they have to be able to trip even if you're holding the lever in the ON position. Have you seen signs of corrosion on yours?

[noelex 77]

The most common failure mode seems to be a deterioration in the contact surfaces. Switching DC results in an arc that produces this deterioration.

The extra contact resistance heats up the breaker so it trips at a lower level. The higher voltage drop can also produce intermittent equipment faults without the breaker tripping.

This failure seems very common on boats over time, especially when the breakers are used as a switch.

The best defence is to install an electrical panel where the breakers are easy to replace, and importantly where identical sized breakers are readily available, preferably from a number of different manufacturers. This is one reason I am a fan of Din rail breakers.

[kayakerChuck]

I had at least one shore power breaker fail in the closed position. I replaced the entire panel and all the breakers. Once I found that it was in the "contact" position no matter the switch position, I didn't bother checking the others & just replaced everything.

1979 O'Day 30.

[SailingHarmonie]

Originally Posted by noelex 77

The most common failure mode seems to be a deterioration in the contact surfaces. Switching DC results in an arc that produces this deterioration.

The extra contact resistance heats up the breaker so it trips at a lower level. The higher voltage drop can also produce intermittent equipment faults without the breaker tripping.

This failure seems very common on boats over time, especially when the breakers are used as a switch.

The best defence is to install an electrical panel where the breakers are easy to replace, and importantly where identical sized breakers are readily available, preferably from a number of different manufacturers. This is one reason I am a fan of Din rail breakers.

noelex,

That makes sense, and it makes a great story. Except...

The breakers that have failed have been in "circuit protection only" use with virtually no switching. Basically always on. The breakers that are used most frequently as switches haven't failed (yet.) No corrosion ever visible, although I did not perform a necropsy on the failed switches. They are all in rigorously dry environments, or as much so as possible on a boat. Oh, yeah, and one of the failures was an AC breaker.

There are no breakers that I use for DC switching of any significant amperage. The only DC breakers routinely used as a switch are for the navigation instrument bus power, so very low amperage, and not cycled a huge number of times. So I'll have to look for something else to blame.

I do share your enthusiasm for the DIN rail breakers. Certainly easy, and simple. All new panels I have installed have gone this way when ever possible.

Unfortunately, the builder of my boat didn't share our opinion. They used the LEAST convenient form factor of any I have ever seen. A French brand of breaker with a unique mounting footprint, awkward to install, expensive, and hard to source. So far I have switched my AC panel over to something easier to deal with, but the DC panel is a much bigger project. I'll get around to it someday.