4 ms·

The same bimetallic break was used in old circuit breakers. You would literally have to wait for the metal to cool down before the connection could be restored.

The same bimetallic break was used in old circuit breakers. You would literally have to wait for the metal to cool down before the connection could be restored. Not sure if it's still used or we use something fancier these days?

delsarto 2y ago
My washing machine door works like that; BigClive has a great teardown which was quite helpful to explain to me why I couldn’t open the door! https://youtu.be/PIm7q_U3UEM?si=K6wUtHJe2Jm8tW6M https://youtu.be/PIm7q_U3UEM?si=K6wUtHJe2Jm8tW6M
- ThePowerOfFuet 2y ago
  Here's that same YouTube link, but without the tracking parameter linking you to everyone who clicks on it: https://youtu.be/PIm7q_U3UEM https://youtu.be/PIm7q_U3UEM
praptak 2y ago
Modern circuit breakers are much fancier. They break not only when the current reaches a threshold but also when the currents passing in both directions (i.e. also back through the ground wire) are unequal. This prevents things like grounding through someone's body.
- deleted 2y ago
  [deleted]
- schiffern 2y ago
  > Modern circuit breakers are much fancier. They break... when the currents passing in both directions [is] unequal What you're describing is properly called GFCI[0] — which in some countries is referred to as an RCD[1] — not just a standard circuit breaker. You can get devices which fit into a standard circuit breaker slot which perform both functions. However a conventional circuit breaker (which are still widely available) doesn't do any of that. [0] Ground Fault Circuit Interruptor [1] Residual Current Device
  - dzhiurgis 2y ago
    Yep I thought my house has that until I tested cheap LED dome light from Aliexpress. It had an exposed screw and I was bare feet in garage (concrete floor). Lesson learned.
  - gjvc 2y ago
    You can get devices which fit into a standard circuit breaker slot which perform both functions in the UK such a device is called an "RCBO" aka "Residual Current Breaker with Over-Current (protection)" good summary here from schneider https://eshop.se.com/in/blog/post/what-is-the-difference-between-mcb-mccb-rcb-rcd-rccb-and-rcbo.html https://eshop.se.com/in/blog/post/what-is-the-difference-bet...
  - epcoa 2y ago
    In fact in the US, especially residential, GFCI circuit breakers are not terribly common for 120V circuits, people much prefer and are used to having the GFCI in the outlet, which can of course protect multiple conventional outlets downstream. But, what is quite common in the last 30 years are AFCIs, arc fault interruptors which are code for pretty much all living area branch circuits (just not bathrooms). These are built in to the circuit breaker. You can get dual GFCI/AFCI breakers, but these tend to be expensive and not commonly used. Nobody wants to have go down to the basement just because of a ground fault in the kitchen. Also the propensity for GFCIs to nuisance trip increases with the length of the branch circuit. There’s also cases where they are specifically disallowed.
    - Suppafly 2y ago
      GFCI outlets also seem to wear out eventually, whether they trip a bunch or not. Lately everyone I know that's sold a house has had to replace one or more of them due to them failing to work during inspections. Part of the issue with "not terribly common" is that no one ever retrofits these things into older houses and new houses only get them where code requires it since it's an increased cost.
      - epcoa 2y ago
- epcoa 2y ago
  > (i.e. also back through the ground wire) are unequal. You mean neutral or return wire. No current should be normally passing through the ground wire. In fact in the US at least, GFCIs can be used on grandfathered ungrounded outlets. When you buy GFCI outlets they come with little stickers: “No Equipment Ground” to affix on the outlet in that case.
cwillu 2y ago
They're still built that way: it has the benefit of properly handling slightly over current for a short period vs massively over-current: the former is permitted and necessary for many loads.
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 ago
  Fun fact, breakers get more sensitive during heat waves. Annoying when it happens.
  - GuB-42 2y ago
    Maybe 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 ago
  It'll trip if you're drawing 10a sustained, you really can only draw 80% sustained to avoid a nuisance trip.
  - Doxin 2y ago
    This 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 ago
    Looking 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
itronitron 2y ago
I assume electric water kettles as well, which shutoff shortly after the water starts boiling.
CoffeeOnWrite 2y ago
My late model Subaru uses this cheap solution for the protection of the infotainment system. If it trips I need to wait for it to cool down for about an hour.

delsarto 2y ago

My washing machine door works like that; BigClive has a great teardown which was quite helpful to explain to me why I couldn’t open the door! https://youtu.be/PIm7q_U3UEM?si=K6wUtHJe2Jm8tW6M https://youtu.be/PIm7q_U3UEM?si=K6wUtHJe2Jm8tW6M

ThePowerOfFuet 2y ago
Here's that same YouTube link, but without the tracking parameter linking you to everyone who clicks on it: https://youtu.be/PIm7q_U3UEM https://youtu.be/PIm7q_U3UEM

praptak 2y ago

Modern circuit breakers are much fancier. They break not only when the current reaches a threshold but also when the currents passing in both directions (i.e. also back through the ground wire) are unequal. This prevents things like grounding through someone's body.

deleted 2y ago
[deleted]
schiffern 2y ago
> Modern circuit breakers are much fancier. They break... when the currents passing in both directions [is] unequal What you're describing is properly called GFCI[0] — which in some countries is referred to as an RCD[1] — not just a standard circuit breaker. You can get devices which fit into a standard circuit breaker slot which perform both functions. However a conventional circuit breaker (which are still widely available) doesn't do any of that. [0] Ground Fault Circuit Interruptor [1] Residual Current Device
- dzhiurgis 2y ago
  Yep I thought my house has that until I tested cheap LED dome light from Aliexpress. It had an exposed screw and I was bare feet in garage (concrete floor). Lesson learned.
- gjvc 2y ago
  You can get devices which fit into a standard circuit breaker slot which perform both functions in the UK such a device is called an "RCBO" aka "Residual Current Breaker with Over-Current (protection)" good summary here from schneider https://eshop.se.com/in/blog/post/what-is-the-difference-between-mcb-mccb-rcb-rcd-rccb-and-rcbo.html https://eshop.se.com/in/blog/post/what-is-the-difference-bet...
- epcoa 2y ago
  In fact in the US, especially residential, GFCI circuit breakers are not terribly common for 120V circuits, people much prefer and are used to having the GFCI in the outlet, which can of course protect multiple conventional outlets downstream. But, what is quite common in the last 30 years are AFCIs, arc fault interruptors which are code for pretty much all living area branch circuits (just not bathrooms). These are built in to the circuit breaker. You can get dual GFCI/AFCI breakers, but these tend to be expensive and not commonly used. Nobody wants to have go down to the basement just because of a ground fault in the kitchen. Also the propensity for GFCIs to nuisance trip increases with the length of the branch circuit. There’s also cases where they are specifically disallowed.
  - Suppafly 2y ago
    GFCI outlets also seem to wear out eventually, whether they trip a bunch or not. Lately everyone I know that's sold a house has had to replace one or more of them due to them failing to work during inspections. Part of the issue with "not terribly common" is that no one ever retrofits these things into older houses and new houses only get them where code requires it since it's an increased cost.
    - epcoa 2y ago
epcoa 2y ago
> (i.e. also back through the ground wire) are unequal. You mean neutral or return wire. No current should be normally passing through the ground wire. In fact in the US at least, GFCIs can be used on grandfathered ungrounded outlets. When you buy GFCI outlets they come with little stickers: “No Equipment Ground” to affix on the outlet in that case.

cwillu 2y ago

They're still built that way: it has the benefit of properly handling slightly over current for a short period vs massively over-current: the former is permitted and necessary for many loads.

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 ago
Fun fact, breakers get more sensitive during heat waves. Annoying when it happens.
- GuB-42 2y ago
  Maybe 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 ago
It'll trip if you're drawing 10a sustained, you really can only draw 80% sustained to avoid a nuisance trip.
- Doxin 2y ago
  This 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 ago
  Looking 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

itronitron 2y ago

I assume electric water kettles as well, which shutoff shortly after the water starts boiling.

CoffeeOnWrite 2y ago

My late model Subaru uses this cheap solution for the protection of the infotainment system. If it trips I need to wait for it to cool down for about an hour.