currentprotectionsafety
Will a standard home automatic circuit breaker, designed and sold as to work on 230V AC (alternating current), and for example 16A, or 25A etc, will it work (break the circuit if it exceeds the rated amperage) on 12V direct current (DC)?
If not, are there any automatic circuit breakers for over-current protection, which work on DC? I mean besides fuses which blow, I want the thing to be reusable with a click, not one-time-use.
This should be covered by IEC 60269. gG and gL is the same thing where gL is an older definintion.
Quote From Wikipedia article about IEC 60269
The application cateogory is a two-digit code. The first letter is a if the fuse is for short-circuit protection only; an associated device must provide overload protection. The first letter is g if the fuse is intended to operate even with currents as low as those that cause it to blow in one hour. These are considered general-purpose fuses for protection of wires.
The second letter indicates the type of equipment or system to be protected:
D – North American time-delay fuses for motor circuits, UL 248 fuses
G – General purpose protection of wires and cables
M – Motors
N – Conductors sized to North American practice, UL 248 fuses
PV – Solar photovoltaic arrays as per 60269-6
R, S – Rectifiers or semiconductors as per 60269-5
Tr – Transformers[citation needed]
Any fuses built to the IEC 60269 standard and carrying the same application category (for example, gG or aM) will have similar electrical characteristics, time-current characteristics, and power dissipation as any other, even if the fuses are made in the packages standardized to the earlier national standards.
Unquote.
The gG/gL 100A that is mentioned in the question should be the fuse current rating. The current that a fuse in series with the device can continously pass through without opening.
According to the comment below, the device marked with gG/gL is a Motor Starter Protector (MSP). This should be put in series with a fuse that won't trip unless a short circuit fault occurs. Not even a stalled motor should trip it. Have a look at Rockwell Automations has a paper "193-2.10: A Guide to Understanding: Short-Circuit Protection" which deals with this. There is mentioned that the fuse should handle approx. 6 to 8 times the Full Load Current. This corresponds quite well to the MSP mentioned in the question.
Here is a picture of how the MSP and Fuse works together:
You're using a 7812 to make 12V from the DC voltage from the bridge rectifier. You need approximately 2V more than 12V to make that work (officially 1.5 or 1.25 I think, but this is safe to use). That means you need 14V from the bridge rectifier.
When rectifying an AC voltage of \$x\$ volt, you get a DC voltage of \$x\cdot\sqrt2\$ volt. That means you will need an AC voltage of \$14/\sqrt2\approx10V\$. With a 24V AC transformeter, you will get a very high DC voltage, about 34V, much higher than necessary. All the other Volts, 34-14=20, will need to be disippated as heat by the regulator. This is not only a waste of energy, but also may cause issues when the regulator gets overheated. A heatsink is a solution, but a transformator that gives you, say, 12V AC would be better.
Best Answer
Use one designed for low voltage DC such as Eaton KD1 or this automotive type. A better option is also a Raychem Polyswitch which self resets when the current is removed. The problem with the 230V ones is the high trip current, have you really got more than 16 or 25 amps available from your 12V supply?
Edit: I didn't realise this related to an earlier question where you are talking about an automotive battery. In that case, yes, many amps are available (as opposed to a wall wart), and Andrew's comment applies - a breaker designed for AC should not be used on DC because it is a harder job to seperate the contacts on a DC current than on AC where the magnetic field falls to zero repeatedly due to the waveform.
MCBs (and fuses) have a characteristic curve showing time to trip against overcurrent. At the rated current, they should last indefinately, but as that is exceeded they trip faster. For a fast trip, you need the source to be capable of many times the rated trip current.