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I want to be able to disconnect the load from a circuit, which may be of variable amperage, possibly up in the hundreds.

I guess what a normal person would do is probably use a contactor of some sort. But then there will be constant consumption in the case of NO, and it will not work with NC because the control unit is part of the load that is to be stopped, so it will just bounce on and off.

It would be best if there was a device such as an automatic circuit breaker that could get triggered with an electronic signal just like it can with that small lever physically. I searched around but I could not find one.

I got a crazy idea of modifying an RCD to add a transistor in the place of the test button, but then remembered that it wouldn't work with DC. I'm just mentioning this to paint you a better picture of what I'm looking for.

Is there such a device?

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    \$\begingroup\$ Sounds like you want a latching contactor. \$\endgroup\$
    – user1937198
    Commented Nov 26, 2023 at 19:19
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    \$\begingroup\$ You can electronically actuate any standard (current-controlled) circuit breaker by shunting the output with a thyristor. This is called a crowbar circuit, and is pretty reliable, though the thyristor might not survive many uses unless it's quite a big one. Alternatively, you can use a GFCI (called an RCD in some regions), which you can manually trip by shunting normal operating current through an alternative path (or even just a handful of mA through that alternative path). \$\endgroup\$
    – Hearth
    Commented Nov 26, 2023 at 19:36
  • \$\begingroup\$ @user1937198 exactly!!! Except I'm not sure if the 12v coil will be strong enough to turn the contactor off. Anyway I got the idea, I can just get an ordinary CB and just attach a mechanism to it to physically trip it, who would have thought... Thank you! \$\endgroup\$
    – php_nub_qq
    Commented Nov 26, 2023 at 19:49
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    \$\begingroup\$ @php_nub_qq You didn't mention that it was DC. You'll need a DC-rated breaker; it's much harder to switch DC than AC (the latter will self-extinguish arcs every half-cycle, the former will not). This will increase cost significantly for something in the hundreds of amps. \$\endgroup\$
    – Hearth
    Commented Nov 26, 2023 at 19:56
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    \$\begingroup\$ 12v coil contactors with latching with 12v 200A rating are available off the shelf: digikey.co.uk/en/products/detail/… \$\endgroup\$
    – user1937198
    Commented Nov 26, 2023 at 20:21

1 Answer 1

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You already have a circuit breaker, right?

They make various types of actuators for these. They're basically an electromagnet that moves a little lever that flips the breaker down. There are also models that flip the breaker up, just in case. Here's one that will flip a breaker in case of fire. It should be connected to a fire detection system.

enter image description here

(pic source is a random Yandex search)

Here's another (pic source) that will also flip your breaker down.

enter image description here

No matter what country you live in, breakers need to be flipped automatically in case of fire, so you'll probably find a compatible local product.

Note AC circuit breakers don't work on DC. With AC, it's difficult for an arc to sustain itself because current stops flowing 100-120 times per second. However with DC, the breaker needs to actively extinguish the arc, for example by using magnets to bend it or other special measures. That's why an AC circuit breaker or switch rated for 250VAC may have an absurdly low rating of 50VDC. If it is used on a DC circuit (and especially on high voltage DC like photovoltaic) it will catch fire and/or explode on first use.

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  • \$\begingroup\$ This is exactly the thing I was about to consider fabricating, thank you! My system is 12V, I'm hoping that it will be low enough for a standard CB to be able to break, of course I will test thoroughly. \$\endgroup\$
    – php_nub_qq
    Commented Nov 26, 2023 at 20:11
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    \$\begingroup\$ 12V should work fine unless you have a huge inductor as a load to make nice sparks \$\endgroup\$
    – bobflux
    Commented Nov 26, 2023 at 20:15
  • \$\begingroup\$ "No matter what country you live in, breakers need to be flipped automatically in case of fire" hm, I haven't been in a country where that is a requirement and also seen it only in some modern non-residential installations... \$\endgroup\$
    – PlasmaHH
    Commented Nov 27, 2023 at 10:47
  • \$\begingroup\$ Around here it's not a requirement, but if some non-residential installations use it then you can buy it, that's my point \$\endgroup\$
    – bobflux
    Commented Nov 27, 2023 at 11:24

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