What is The Miniature Circuit Breaker?

Automatic circuit breakers or miniature circuit breakers are protective and switching circuit elements designed to protect the electrical installation against overloads and short circuits. If the current passing through the circuit exceeds a certain level of the rated (declared) currents of the breaker or a short circuit occurs in the circuit, the miniature circuit breaker breaks the electrical connection and protects the circuit after itself.

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Figure-1: Miniature Circuit Breaker with 4 Pole

What are the main features of miniature circuit breakers?

• Production in accordance with IEC / TS / EN / CE standards and directives
• Rated current range between 0.5 and 125A.
• Short circuit breaking capacity up to 10 kA
• 230 / 400V AC operating voltage
• 250V DC operating voltage per pole(1P: 250V / 2P: 500V / 3P: 750V / 4P: V)
• 60V DC operation voltage for the breakers manufactured for AC systems
• Different pole options as 1P, 2P, 3P, 3P+N and 4P.
• Fixed thermal protection and B / C / D type magnetic protection characteristics (B: 3-5 In, C: 5-10 In, D: 10-20 In)
• Calibration up to 55 oC working temperature according to demand.
• Terminals suitable up to 50 mm2 cable
• Facility to equip with accessories such as opening coil and auxiliary contact block
• Thermoplastic body resistant to high temperatures
• Production sensitive to human health under RoHS conditions
• Deep connection terminals to prevent direct hand contact
• Terminals suitable for comb type busbars
• Trip free mechanism
• Current limiting against thermal and magnetic stresses with fast breaking feature
• Colored position indicator
• Sealing ability
• Mechanism resistant to mechanical shock, impact and vibrations
• Facility to input energy from the upper and lower terminals

What is the Working Principle of Miniature Circuit Breakers?

The main parts of the internal mechanism of miniature circuit breakers are shown in Figure-2. The current is applied from the input terminal. Then, the current is transferred through flexible copper from the input terminal to a structure called bimetal and transferred from the bimetal to the magnetic coil thorugh another flexible copper, from the coil to the moving contact again with flexible copper, as a result of the contact between the moving contact and the fixed contact, the current is transferred to the output terminal via the fixed contact. Briefly, in an miniature circuit breaker, the current follows this way. The current is checked by means of thermal and magnetic protection devices while following this way in the breaker. Thermal protection (overcurrent protection) is carried out by bimetal and magnetic protection (short circuit protection) by the coil.

Bimetal is formed by combining different metals with different elongation coefficients. With this structure, bimetal starts to warm up as the breaker starts to be loaded over a certain level above the nominal current .The metal with a high elongation coefficient in bimetal is heated, expands towards the metal with a small elongation coefficient and bends and takes the form of brackets “(” .With the change of form of bimetal, the mechanical opening mechanism is triggered and the breaker opens the circuit. This protection made over bimetal is called thermal protection. Thermal protection occurs when the current of the breaker passes a certain level above the nominal current of the breaker.

In case of a high current short circuit in the electrical circuits, the electrical installation is protected by the magnetic protection device of the miniature circuit breakers. In the internal mechanism of the breaker, the current passes over the magnetic coil with a flexible copper connection after the bimetal structure. With the formation of a short circuit in the circuit, this high current also passes over the coil in the breaker. When the short circuit current reaches the level to load the coil as a magnetic field, the shaft inside the coil’s core is drawn by magnetizing. With the movement of the shaft, the opening device is triggered mechanically and the moving contact is separated from the fixed contact. In this way, the breaker goes into the open position and the circuit is de-energized. The magnetic protection device provides protection by acting on the 3, 5, 10 times of the nominal (enounced) current of the breaker.

In miniature circuit breakers, two-point tripping is provided, namely thermal and magnetic protection. The opening mechanism of the breaker is triggered by bimetal in overcurrent, in short circuit current, it is triggered by the shaft in the coil.

There are arc chambers in the breaker internal mechanism to extinguish the arc coming out during the breaking as soon as possible. The arc chamber is located within the working area of ​​the moving contact. The arc formed between the movable and fixed contact during breaking is extinguished by extending it through the magnetic field by the sequenced metal plates on the arc chamber.

Figure-2: Internal Mechanism of Miniature Circuit Breaker

What Are The Miniature Circuit Breakers Types and How to Choose Them?

Miniature circuit breakers are named in B, C and D types according to different opening characteristics. Type B circuit breakers are used for lighting and resistive loads in homes and similar places. Type B breakers open the circuit through the magnetic coil in case of a short circuit current of 3 to 5 times the rated currents. Type C and D breakers are for industrial areas and are used in inductively loaded circuits (motor, transformer circuit, etc.). Due to the sudden inrush currents occurring in these circuits, a tolerance must be shown. C and D type breakers perform magnetic protection 5-10 times and 10-20 times respectively of the rated currents.

Miniature Circuit Breaker Type Characteristic Place of Use B I1 (t>1h) 1.13 x In Home and similar places /Lighting, resistive loads I2 (t<1h) 1.45 x In I3 (t>0.1s) 3 x In I4 (t<0.1s) 5 x In C I1 (t>1h) 1.13 x In Industrial areas /Inductive loads I2 (t<1h) 1.45 x In I3 (t>0.1s) 5 x In I4 (t<0.1s) 10 x In D I1 (t>1h) 1.13 x In Industrial areas /Inductive loads I2 (t<1h) 1.45 x In I3 (t>0.1s) 10 x In I4 (t<0.1s) 20 x In

Table-1: Miniature Circuit Breakers Magnetic Opening Characteristic Table

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The current value is written on the circuit breakers without the symbol (A). With the expressions like B16, C25, the type of the circuit breaker and the rated current value are specified. These factors should be considered in the selection of circuit breakers. According to the standards, miniature circuit breakers are generally produced in nominal current values of 1A, 2A, 3A, 4A, 6A, 10A, 16A, 20A, 25A, 32A, 40A, 63A, 80A, 100A and 125A. These current values on the circuit breakers indicate the currents that the circuit breakers will carry continuously. The rated current passing through the circuit to which it is connected must be below the circuit breaker rating current. When choosing a circuit breaker, the load characteristics (resistive, inductive) should be analyzed first and the circuit breaker type (B, C, D) should be chosen correctly accordingly. Practically, the circuit breaker rated current is selected approximately 1,2 times the nominal current drawn by the load connected to the circuit.

The Importance of Using Miniature Circuit Breakers?

The benefits and conveniences of electricity for human life are too many to count. In daily life, devices used in residences, factories, hospitals and many different fields operate with electrical energy. While electrical energy provides these conveniences to people, it can also cause great disasters due to imprudence and carelessness. In order to protect human health, electrical installation, structure and devices from negative consequences of electricity, protection elements are used in circuits.

Miniature circuit breakers, one of the protection elements, protect the subsequent installation and load against overcurrent and short circuit conditions. However, they cannot protect human life. In order to protect human life against direct and indirect contacts, residual current circuit breakers are used in the circuits. Miniature circuit breakers do not provide protection against residual currents at very small amperage levels that may pose a risk to human life. Rated current values of miniature circuit breakers are selected according to the amount of current drawn by the load in the circuit. The circuit breaker will not open unless the current passing through the circuit exceeds a certain level of rated current of the breaker. Therefore, miniature circuit breakers protect the connected installations and devices against over currents and short-circuit currents. The electrical or physical damage caused by high short circuit currents in the installation and load is prevented. Damage caused by overcurrent or short circuit currents in cable insulations or load insulation may pose a risk of fire. These fault currents are detected and the circuit is cut in a short time with these protection elements.

How to Connect Miniature Circuit Breakers?

Miniature circuit breakers perform thermal and magnetic protection functions in circuits. In residential or industrial areas; It can be used as main or distribution circuit breaker in lighting, heater and motor circuits. Depending on the assembly of the miniature circuit breakers in the panel, energy can be input from the upper or lower terminals. The use of miniature circuit breakers is as follows ;

1. pole in a single-phase circuit without neutral interruption,
2. poles in a single phase circuit with a neutral interrupt,
3. poles in a three-phase circuit without neutral interruption
4. pole in a three-phase circuit with a neutral interruption.

The point that should be considered in the input and output connections, from which terminal phase input is made, phase output should be made from the corresponding terminal.

In neutral circuit breakers, the neutral terminal is marked by the letter “N”.

Neutral terminal can be manufactured unprotected according to customer demand. For this reason, it should be ensured that the neutral line in the circuit is connected to the neutral terminal specified in the circuit breaker.

Figure-3: Connection of Terminals

Miniature Circuit Breakers Use in DC

Direct Current (DC) is used in many fields such as automation circuits, communication devices, dc electric motors, coating rectifiers in plants, solar power plants, solar roof systems. In DC energy, current does not change direction in (+) and (-) alternans as in AC energy. For this reason, DC current is more difficult to cut by circuit breakers. DC current that does not exceed 0 (zero) point creates an arc that is difficult to break by circuit breakers. Due to the AC current passing through the 0 (zero) point and constantly changing direction, the arc formed during cutting in AC current is extinguishedmore quickly. Magnetic routers are used in DC circuit elements to extinguish the arc formed during the breaking operations performed by circuit breakers because the DC current does not change direction. The arc formed by this magnetic routers is pushed towards the separators (arc chambers). Thus, the arc is provided to be extinguished in less time without damaging the contact surface.

Federal miniature circuit breakers manufactured for AC systems can be used at 60V DC voltage at rated currents. It is used in systems such as 60V DC requirement, solar energy, generator and control circuits. In automation circuits, the input (output) and output (output) voltages of the controller (such as PLC) are usually 24 V DC. For this reason, standard AC miniature circuit breakers can also be used in DC circuits in many areas. For the needs above this working voltage, DC miniature circuit breakers with 250V DC working voltage per pole are included in the product range.

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I am interested in safely using MCBs (mini circuit breaker) wherever possible in my solar setup; however after reading all the threads and web search matches I can find on the subject, I would like to clarify the following:

Questions
1. Is there a way to test for polarized vs. non-polarized MCBs with a multi-meter or otherwise? If so, please reply with the steps for the benefit of the community.

2. If a MCB is not magnetic, can we automatically conclude that it is not polarized, and the direction of the flow of current is not important, or are there other factors to consider?

I have a number of MCBs I purchased from AliExpress. The Tomzn (trip curve B) and EARU (trip curve unclear) breakers are magnetized, and the TAIXI 150A (trip curve B) breakers are not magnetic.

My setup includes a Growatt ES hybrid inverter (US version), 16s EVE 280Ah battery with 200A JBD BMS and W solar panel array. In addition to the MCB to battery, I will also be using 200A T-Class Fuses.

My Magnetism Tests On Camera


My Preliminary Conclusion

The TOMZN and EARU breakers are magnetic and therefore probably polarized MCBs, only supporting current flow protection in ONE direction, rather than supporting bi-directional current flow protection. These should be used only for one directional current, such as PV in from the solar panels.

The TAIXI are not magnetic, and therefore probably not polarized MCBs, and can be used for bi-directional current, such as between a battery and and a hybrid inverter device. Please correct me if this is wrong.

I love the clean DIN rail mount option rather than other ugly form factor switching methods, but will not use this setup if it is unsafe. I'm hoping this thread can bring accurate responses and safety to the community at large.


I have recently been in touch with Nanque Electric Store on AliExpress, and they are assuring me that their DZ47-63 series breakers (DC12-120V) and NQCM1-600 series breakers (DC-12-120V) are non-polarized, and support bi-directional current protection from battery to inverter. If this is true, they could be a good options.



















From the DZ47-63 product listing












References:

• http://greenforcesolar.com.au/wordp...of-Double-Pole-DC-Breakers-LVL2--v2.pdf
• https://www.altechcorp.com/PDFS/DC wiring_white paper_Altech DC series_.pdf

@Charleswgibbs @Phil.g00 @hgg @Hedges @BradCagle @Will Prowse

Manufacturers data will tell you what you need to know.
Don't rely on technical information from a salesperson, especially a foreign one.
Do your own research to satisfy yourself and AHJ.
If you need to get a permit most of these units are no good to you.

With respect,
1. I do not trust manufactures data when purchasing from overseas. In this case I wish to confirm proper operation myself by physically testing.
2. If I trusted the salesperson I wouldn't be here. I made this post because I don't trust the salesperson, and am looking for practical insight from those who have physically tested and understand MCBs, and can provide clarity for the rest of us to do our own testing.
3. I have been researching this topic for days, and have spent extensive hours learning about the subject. If you know the answers to my questions, please post them, or links online where the answer has been given. I'd be very grateful!
4. There are no permits where I live. I also got some125A and 160A TAIXI MCCBs from Aliexpress. They are not magnetized from my research.
Seller also said its OK to connect loads at the top, even though they diagram shows otherwise.
But because of the diagram and positive/negative symbols, I was reluctant to use them (wasted money).
In the end I went for this as my main breaker, since it says specificly that it NOT polarized:

Yes, it more costly than the TAIXI breakers, but I wanted to be safe. Also, the size if this breaker is HUGE ! Even larger than the 160A TAIXI breaker, which at the time I thought is pretty large.
Seems like quality stuff.
I guess I will save my TAIXI for workbench testing purposes, or for uses which are only in one direction.

Another option is this one:

ZJ BENY Bdm 125A Dc Circuit Breaker

NOARK DIN MOUNT MINIATURE CIRCUIT BREAKER EX9BN
Under specifications it says: No polarity.
Unfortunately I was only able to get it from an Aussy supplier who agreed to ship to Middle-East. Shipping cost me a fortune, but maybe you will be able to find this model with local (or cheaper) shipping rates.
I plan to use the 125A ZJBENY as my battery breaker (one for each 24v battery) so that I can isolate one battery if it needs maintenance etc... while the other battery continues to power my inverter.

I am interested in safely using MCBs (mini circuit breaker) wherever possible in my solar setup; however after reading all the threads and web search matches I can find on the subject, I would like to clarify the following:

Questions
1. Is there a way to test for polarized vs. non-polarized MCBs with a multi-meter or otherwise? If so, please reply with the steps for the benefit of the community.

2. If a MCB is not magnetic, can we automatically conclude that it is not polarized, and the direction of the flow of current is not important, or are there other factors to consider?

I have a number of MCBs I purchased from AliExpress. The Tomzn (trip curve B) and EARU (trip curve unclear) breakers are magnetized, and the TAIXI 150A (trip curve B) breakers are not magnetic.

My setup includes a Growatt ES hybrid inverter (US version), 16s EVE 280Ah battery with 200A JBD BMS and W solar panel array. In addition to the MCB to battery, I will also be using 200A T-Class Fuses.

My Magnetism Tests On Camera


My Preliminary Conclusion

The TOMZN and EARU breakers are magnetic and therefore probably polarized MCBs, only supporting current flow protection in ONE direction, rather than supporting bi-directional current flow protection. These should be used only for one directional current, such as PV in from the solar panels.

The TAIXI are not magnetic, and therefore probably not polarized MCBs, and can be used for bi-directional current, such as between a battery and and a hybrid inverter device. Please correct me if this is wrong.

I love the clean DIN rail mount option rather than other ugly form factor switching methods, but will not use this setup if it is unsafe. I'm hoping this thread can bring accurate responses and safety to the community at large.


I have recently been in touch with Nanque Electric Store on AliExpress, and they are assuring me that their DZ47-63 series breakers (DC12-120V) and NQCM1-600 series breakers (DC-12-120V) are non-polarized, and support bi-directional current protection from battery to inverter. If this is true, they could be a good options.



















From the DZ47-63 product listing












References:

• http://greenforcesolar.com.au/wordp...of-Double-Pole-DC-Breakers-LVL2--v2.pdf
• https://www.altechcorp.com/PDFS/DC wiring_white paper_Altech DC series_.pdf

@Charleswgibbs @Phil.g00 @hgg @Hedges @BradCagle @Will Prowse

This is very interesting. I asked them the same thing a few hours ago concerning current protection in either direction for the 150A model and was told it would only protect in a single direction. I may still use them however. For my setup, I'm only relying on the breaker as a disconnect switch for the battery. I'm using t class fuses on each battery and my reliance is on the fuse, in addition to having the BMS and inverters with the necessary over current protection settings.

This is very interesting. I asked them the same thing a few hours ago concerning current protection in either direction for the 150A model and was told it would only protect in a single direction. I may still use them however. For my setup, I'm only relying on the breaker as a disconnect switch for the battery. I'm using t class fuses on each battery and my reliance is on the fuse, in addition to having the BMS and inverters with the necessary over current protection settings.

One day you will open that MCB under some load (it does not have to be huge) and fireworks will start. In this case, that inline fuse will not protect you as the AMPS will not be massive either.

One day you will open that MCB under some load (it does not have to be huge) and fireworks will start. In this case, that inline fuse will not protect you as the AMPS will not be massive either.

Could you please explain why so we can learn? If the breaker is indeed non-polarized, and does not direct the arc with magnets in one direction only, why would there be fireworks? I genuinely would like to know.

I also want to clarify that the TAIXI 150A breakers in my original post are the only ones that I presume to be non-polarized, and that might be an option for a battery disconnect switch and breaker function. The other two brands I know can only be used for current protection in one direction.

Could you please explain why so we can learn? If the breaker is indeed non-polarized, and does not direct the arc with magnets in one direction only, why would there be fireworks? I genuinely would like to know.

I also want to clarify that the TAIXI 150A breakers in my original post are the only ones that I presume to be non-polarized, and that might be an option for a battery disconnect switch and breaker function. The other two brands I know can only be used for current protection in one direction.

Was actually going to ask the same question ecspecially when I see the big brand server rack batteries using similar breakers that one would get on amazon and aliexpress.

I would think that for a DC rated breaker, magnet and polarized go hand in hand.
The DC47, I think I see 6k amp interrupting for 100A model, 4k amp interrupting for 63A model.
That's in the short circuit current range of lead-acid, not lithium. Maybe class T fuse in series will prevent catastrophic failure. But it isn't "current limiting", will likely leave breaker ruined.

"DC MCB 12V 24V 48V 60V 110V" "DC 12V ~ 120V" I'm going to guess 120V, 110V, and maybe 60V, requires two poles in series.

If you're going to take a chance with one of these, maybe test by loading to rated voltage and over-current so it trips, in both polarities?
(Are they spec'd to function many times, like UL listed breakers are?)

I ended up ordering two of the larger MCCB (Moulded Case Circuit Breakers). I will test to the best of my ability upon arrival, but I don't think I have a way to test more than about 120A load.

1. TAIXI DC12V 24V 48V 250A Moulded Case Circuit Breaker Battery 100A 200A 300A 400A 600A MCCB Car Charging Pile Protector
I got the 2 Pole, 200A version

2. TOMZN 2P DC 600V DC Solar Molded Case Circuit Breaker MCCB Overload Protection Switch Protector for Solar Photovoltaic PV
I got the 2 Pole, 250A version

Once again, my desire is to use one of these circuit breakers between my 280Ah battery and my Growatt ES inverter, as well as a 200A class T fuse. I appreciate @Hedges pointing out the low "amp interrupting" capacity on the smaller MCBs.

In light of this, I think the MCCB would be the only path I will consider at this point. The MCCB switches that are on the way have 25kA (TAIXI) breaking capacity and 35kA (TOMZN) breaking capacity, vs the smaller 6kA (TAIXI) 150A MCBs in my original post. Please feel free to chime in, but I believe 25kA + should be fully adequate to handle breaking current for my 16, 280Ah lithium cells in series (48v nominal).

The TAXI MCCB I ordered says it has an electrical life of times (switching on and off).
The TOMZN MCCB I ordered does not have this spec listed. I would assume it to be similar.

I plan to get a thermal camera, to monitor these breakers under load, to ensure they are not getting hot inside with normal load, which in my case will be around 60-110A.