Using 220v circuit breaker at 12v

[ruvane]

Would a circuit breaker rated at say 220VAC and 10A still perform the same way and trip at 10A if used in a 12VDC circuit?

My head says yes and my gut says no!

TIA,
Ruvane.

 

[jdc]

It might but it'll depend on how it's constructed. If purely mechanical with a bi-matallic strip then all it takes to trip it is current, which heats the bi-metallic element. It has no knowledge of the Volts after-all, and DC is just as heating as the RMS AC current.

However many breakers are more sophisticated and no longer have bi-matallic strips but measure the current electronically with a current transformer, and calculate the possible temperature rise in the wiring, torques or other strains in a load and even electric shock risk. They also are rather clever in arranging that it's always the most down-stream breaker trips and none up-stream of this, what's known as 'selectivity'. To power all this signal processing you need the current transformer to deliver secondary current, and that means AC not DC.

Note: RCCBs work with AC only.

 

[wongaero]

The manufacturer's data sheet will say if the device is rated for DC - I don't think there's a safe rule of thumb because DC contacts require careful design to deal with the increased tendency toward arcing compared with AC use

 

[rogerthebodger]

The manufacturer's data sheet will say if the device is rated for DC - I don't think there's a safe rule of thumb because DC contacts require careful design to deal with the increased tendency toward arcing compared with AC use

The arcing in a DC circuit is a function of both current and voltage for a particular breaker design.

This is why a circuit breaker of a particular current rating will have a lower working voltage when used on DC.

I know miniature circuit breakers rated at 240 VAC are rated at 32 VDC the is the derate in voltage due to the switching arc but the current rating is always the same.

This kind of derate also applies to any switching device like relays of toggle switches.

 

[superheat6k]

Most basic 240v MCBs (rather than more complex MCCBs) will work fine on 12 v DC, but be careful to select a faster trip curve, e.g. A or B curve. C & D curve will take longer to operate and are intended for use on heavier inductive AC loads such as motors. However for a heavy load like a windlass then a D curve would be more effective, although even a 63amp (the largest MCB size available) would be a bit under-rated.

We use a make called Chint in our business and these are widely sold on Ebay for sensible prices.

 

[PaulRainbow]

Don't forget, for a windlass you need a thermal circuit breaker.

 

[David2452]

As above, some will and some will not, I see them used quite frequently and of course the right spec will give you the coverage required. Should you is another question, personally I would not due to both size and potential for future confusion.