Mechanical to Electronic Circuit Breaker

[SND_Dev]

a tldr:
I was wondering if its possible to use a current sensor, a comparator and relay to replace (in functionality) the 240VAC mechanical circuit breakers currently in use. Would they be as reliable and safe as the mechanical ones ?

the backstory:

So, a friend of mine wanted a way to control the circuitry at his home via smart phone, following the "smart house" hype I'd assume. He came to ask me about how to go about doing that. Since 240VAC isn't my area of expertise I was very hesitant to give him a clear answer.

I mainly work with digital circuits for micro-controllers, specifically arduino. so im very wary and skeptical when it comes to voltages as high as 240V. I do understand the theory when it comes to power electronics, but i'm missing the practical experience.

I thought about it for some time and I thought "If you can switch on/off the circuit breaker, than that's basically controlling the circuitry of every room in the house", not sure if that's a good idea though but that's where I am now in the thought process.

The reason I picked the circuit breakers is because they're all gathered in the distribution box, making it easier to install for the entire house.
And the reason for "electronic" from "mechanical" is that way it can be controlled by a micro-controller.

Any insight on the subject is appreciated. Thank you 

[mikeselectricstuff]

The problem is not so much getting them to work - Solid-State relays work fine, but showing that they will always fail safe. Semiconductors often fail short.

[rstofer]

At one time, I believe, Square-D made a line of electrically switchable circuit breakers.  I didn't turn up anything on Google.

The way it is usually done is to use switching relays of appropriate rating.  It was fairly common to have a panel full of relays right next to the panel full of circuit breakers for lighting circuits.  Something like the GE RR-7 is commonly used in 277V lighting here in the US.

http://www.relectric.com/Store/Motor-Control-Parts-%26-Accessories/RR7/FSSS?gclid=CK7K-PrvvNECFZSIfgodcM0Cpg

These relays don't have to be centralized, they are made to fit in a standard knock-out on a junction box such that the high voltage end is inside the box and the low voltage wires are exposed.  Low voltage (and low current) wiring is just run wherever it is necessary.

These relays can be controlled by a uC.  Just about 40 years ago I built a system using an industrial uC and modems to control lighting in a 300 ksf building and another two remote buildings.  It worked well.

There is nothing you can build up that will have the required certifications.  You can buy whatever listed components you need but you can't really invent them.  I doubt that you will find electrically switchable breakers for an existing panel.

[Siwastaja]

Keep the mechanical circuit breakers - they are there for a good reason. They are unaffected by software bugs and require someone's local, physical attention to restore the power - which is a good thing.

Add any "Arduino" controlled relay stuff after the breakers.

[MarkL]

Electrically controllable circuit breakers are available.  Search for "remote control circuit breaker".  They're not cheap.

Eaton/Cutler-Hammer and Schneider/Square-D are a couple of manufacturers.

The Eaton devices are a circuit breaker and latching relay in one package.  So, all the protection is still there.  If the breaker trips, you still have to reset it manually, but as long as it's not tripped, you can control the load remotely:

  http://www.eaton.com/Eaton/ProductsServices/Electrical/ProductsandServices/CircuitProtection/IndustrialMiniatureCircuitBreakers/RemoteControlledCircuitBreakers/index.htm

The Square-D PowerLink breakers have a motor in them which can actuate the breaker handle.  But if it trips it still has to be manually reset, if I'm reading the specs right:

  http://www2.schneider-electric.com/resources/sites/SCHNEIDER_ELECTRIC/content/live/FAQS/228000/FA228072/en_US/1210CT0201.pdf

Whether these fit in an existing breaker panel is another matter.


Turning whole circuits on and off is probably not what you want for a home automation system anyway.  Home wiring circuits are rarely and conveniently just a single room, or wired to just the outlets you want.

Take a look at X10 or other home automation system that can do per-outlet control:

  http://www.x10.com

[CM800]

Electrically controllable circuit breakers are available.  Search for "remote control circuit breaker".  They're not cheap.

Eaton/Cutler-Hammer and Schneider/Square-D are a couple of manufacturers.

The Eaton devices are a circuit breaker and latching relay in one package.  So, all the protection is still there.  If the breaker trips, you still have to reset it manually, but as long as it's not tripped, you can control the load remotely:

  http://www.eaton.com/Eaton/ProductsServices/Electrical/ProductsandServices/CircuitProtection/IndustrialMiniatureCircuitBreakers/RemoteControlledCircuitBreakers/index.htm

The Square-D PowerLink breakers have a motor in them which can actuate the breaker handle.  But if it trips it still has to be manually reset, if I'm reading the specs right:

  http://www2.schneider-electric.com/resources/sites/SCHNEIDER_ELECTRIC/content/live/FAQS/228000/FA228072/en_US/1210CT0201.pdf

Whether these fit in an existing breaker panel is another matter.


Turning whole circuits on and off is probably not what you want for a home automation system anyway.  Home wiring circuits are rarely and conveniently just a single room, or wired to just the outlets you want.

Take a look at X10 or other home automation system that can do per-outlet control:

  http://www.x10.com

Why do you think they are designed so they can't be remotely reset?

[SND_Dev]

The problem is not so much getting them to work - Solid-State relays work fine, but showing that they will always fail safe. Semiconductors often fail short.

yep, that was my highest concern. seems much safer to stick with mechanical

Keep the mechanical circuit breakers - they are there for a good reason. They are unaffected by software bugs and require someone's local, physical attention to restore the power - which is a good thing.

Add any "Arduino" controlled relay stuff after the breakers.

good point. I think adding remote controlled relays as light switches and outlets is the best way to go, but then I'll have to run a 5V power line to power up each module in every room, or use batteries but that's undesirable since it requires replacing after a while.

[Frost]

The reason I picked the circuit breakers is because they're all gathered in the distribution box, making it easier to install for the entire house.

What you are looking for is a Switch Actuator
Normally they are mountet together with the circuit breakers in the distribution box,
but the did not replace the circuit breakers.
http://www.knx-gebaeudesysteme.de/sto_g/English/_HTML/product_2CDG110134R0011.htm
Teh relays used in this devices are latching relays, so they only
need power when they change their state.

[DBecker]

There are various devices that have the functionality of an electronically controlled circuit breaker.  A good example is a EVSE (electric car charging cord).  They typically implement both GFCI and overcurrent protection using a non-latching mechanical relay.

A solid state relay is not safe in this application because they usually fail shorted and they have significant off-state leakage current.  The preferred device is a contactor with a symmetrical draw frame that pulls in full floating two point moving contacts.  This switches both legs or all phases simultaneously, with each conductor having two contact points.

An alternate implementation is two independent single pole relays, but these don't always meet certification requirements for hard-wired installation.

Both designs have output voltage monitoring and will not reset if one relay contact fails welded closed.  Output current monitoring is used to monitor the load for over-current of a ground fault.  Latching relays are never used to avoid problems with brown-outs and power failures.  (In contrast to lighting control devices, which usually do latch so they stay in their previous state even during power glitches.)

[vk6zgo]

You need the device that we used to call a "Contactor",which were/are widely used in large Radio transmitters
They are used in addition to a normal circuit breaker,but have no inbuilt overload function,& are controlled by external circuitry, using either relay logic or electronic logic circuits.

When they are not energised,they remove the Mains supply from the following circuitry,but are not normally regarded as a substitute for a standalone circuit breaker.

[coppice]

There are quite a few breakers available which use electronics to sense when to break, and mechanical contacts which actually break the circuit. One of the main reasons makers like this is one design can suit a variety of breaking currents, and the installer can select the one they want at the time of installation. An electromechanical breaker is so cheap, and its design is so well proven over decades, that I am skeptical about electronic breakers becoming dominant, but they are definitely out there.

Electronically triggered RCB devices are already quite common. There are ASICs from a couple of sources to implement these at low cost.

[MarkL]

Why do you think they are designed so they can't be remotely reset?

I couldn't find any NEC or other code that specify no remote reset, but applying common sense I'd say it's for safety's sake.  If a circuit breaker trips, there's a demonstrated safety problem and it should be investigated and resolved.  I wouldn't want some microcontroller issuing mindless resets and continuously re-energizing a circuit that's overloaded or shorted.  It's a good recipe for burning down the house, or electrocuting someone who might be working on the circuit.

I found some datasheets for very large class breakers used in building power distribution systems that can be remotely reset (Eaton IZMX series).  Maybe something exists out there for a house, but I haven't encountered it.