3 ms·
Bimetallic strips are still used these days, but it is often not the only trigger. The bimetallic strip is for overcurrent protection over a period of time. Fo
by GuB-42 2y ago
Bimetallic strips are still used these days, but it is often not the only trigger.
The bimetallic strip is for overcurrent protection over a period of time. For example, if you are running an appliance using a constant 15A on a 10A breaker. The breaker will pop, but not instantly, and I guess you may have to wait a bit for the metal to cool down, though it never happened to me.
But there is also a short-circuit protection, it uses a solenoid to quickly trip the breaker when the current is way over its rating. The fancier types (with GFCI) also pop if the return current is not the same as the input current, this is to prevent electrocution.
- Projectiboga 2y agoFun fact, breakers get more sensitive during heat waves. Annoying when it happens.
- GuB-42 2y agoMaybe it is an unintended but actually beneficial effect. The problem with drawing too much current is that things can overheat, and it is more of a problem during heat waves as well.
- nullc 2y agoIt'll trip if you're drawing 10a sustained, you really can only draw 80% sustained to avoid a nuisance trip.
- Doxin 2y agoThis depends on the country you're in. As far as I understand breakers here are rated for 100% the rating they are labeled as.
- GuB-42 2y agoLooking at the curves published here[1], no breaker should trip with a current draw under its rating, the tolerance goes the other way. For example, after 1h, at 30°C, a breaker should not trip if the current is less than 113% of its rating, and it should trip if it is more than 145%. [1] https://www.tekdok.dk/files/CA908024E_Trip_curve_2021.pdf https://www.tekdok.dk/files/CA908024E_Trip_curve_2021.pdf
- nullc 2y agoInteresting, I've certainly had nuisance trips at <100% looking at https://www.ece.uprm.edu/~lorama/Square%20D%20CB%20Curves.pdf https://www.ece.uprm.edu/~lorama/Square%20D%20CB%20Curves.pd... page 36 you can see even at the rated 25c ambient it goes below 1 (though not as low as 0.9, much less 0.8 rule of thumb). I haven't given it a lot of research because NEC requires 125% (1/.8) for continuous loads (for conductor protection). Perhaps my experience was hot ambient/panel.