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The tripping characteristics of circuit breakers are A, B, C and D.
So how do we choose?
(1) Type A circuit breaker: 2 times rated current, rarely used, generally used for semiconductor protection (fuse is generally used);
The so-called how many times the current, is the shock current, withstand a certain duration of the switch does not trip, its characteristics is to avoid the impulse current.
Selection of tripping device for low-voltage circuit breakers: tripping device types for circuit breakers include over-current tripping device, under-voltage tripping device, shunt tripping device, etc.
Over-current trip can also be divided into overload trip and short-circuit current trip, and there are long delay, short delay and instantaneous. Over-current trip is most commonly used.
The operating current setting value of the overcurrent trip may be fixed or adjustable, usually by means of rotation or adjustment lever.
Electromagnetic over - current trip is also fixed and adjustable.
Electronic overcurrent trippers are generally adjustable.
The breaking capacity of a circuit breaker refers to the capacity to withstand the maximum short-circuit current, so the breaking capacity of a rotating circuit breaker must be greater than the short-circuit current of its protection equipment.
Overcurrent trip according to the installation and can be divided into fixed installation or module, fixed for the installation of the factory trip and circuit breaker is processed into an organic whole, once after they leave the rated current of the trip is adjustable, and modular installation trip as a circuit breaker installed modules, can be adjustable, flexibility is strong.
Instantaneous type: 0.02s for short circuit protection;
Short delay: 0.1-0.4s for short circuit and overload protection;
Long delay: less than 10S for overload protection;
At present commonly used DZ series air switch (with small leakage protection circuit breaker), common specifications have: C16, C25, C32, C40, C60, C80 and alkane, etc., including C, C, the tripping current feature of the current is C20 said takeoff current of 20 a, for example, tripping characteristics for C curve, general installation w heater should choose C20 circuit breaker, installation of water heater of w with C32 circuit breakers.
Circuit breakers are designed to protect wires and prevent fires, so they should be selected according to the size of the wires rather than the power of the electricity.
If the circuit breaker selection is too large to protect the role of the wire, when the wire overload circuit breaker will still not jump, it will bring hidden dangers to the family security.
1.5 square line with C10 switch
2.5 square lines with C16 or 20 switches
4 square lines with C25 switch
6 square lines with C32 switch
For the air switch used for the load motor, the D-type characteristics should be selected to avoid the motor starting 5-8 times the high starting current.
(2) B-type circuit breaker: 2-3 times rated current, generally used for pure resistive load and low-voltage lighting circuit, usually used for household distribution boxes, to protect household appliances and personal safety, less used at present.
(3) Type C circuit breaker: 5-10 times the rated current, need to trip within 0.1 second, this characteristic of the circuit breaker is the most common, often used to protect distribution lines and lighting lines with high switching current.
(4) D circuit breaker: 10-20 times the rated current, mainly in the use of electric appliances instantaneous current larger environment, the general family is also relatively less, suitable for high inductive load and large impulse current system, often used to protect the equipment with high impulse current.
II. Whether the C-type circuit breaker is suitable for the motor circuit
We all know that C-type microfractures are used in common circuits, such as lighting circuits;
Type D circuit breaker is used in motor and other power circuits. Then, can type C micro break be used in motor circuits?
Let's look at the difference between type C and Type D microfractures first, without saying whether it's ok or not:
Type C micro break: it contains overload protection and short circuit protection. The short circuit protection trip value is 5~10 times of rated current.
Type D microbreak: it contains overload protection and short circuit protection. The short circuit protection trip value is 10~20 times of rated current.
The overload protection is the same between the two except the short circuit protection trip range.
Normally, the normal load has no starting current, that is, the starting current is the rated current;
The starting current of the motor is 7~10 times of the rated current.
Example: 4kW three-phase motor, rated current 9A, starting current calculated by 10 times, 90A;
Usually, type D 16A micro break is selected as the protection electrical appliance. The action current of short-circuit protection is 160A according to 10 times of the action current, which can avoid the starting current of the motor.
Then, if 16A micro break of Type C is selected as the protection electrical appliance, the action current of short-circuit protection is 80A according to 5 times of the action current, which cannot avoid the motor starting current.
Does that mean you should never choose a C circuit breaker?
Of course not. If the type C 25A micro break is selected as the protection electrical appliance, the short-circuit protection action current is 125A, which can avoid the motor starting current.
With competitive price and timely delivery, Sager sincerely hope to be your supplier and partner.
There are no technical problems.
The economy
Taking Schneider C65 series microfracture as an example,
C65N 3P C25A is 130.3 yuan
The price of C65N 3P D16A is 158.9 yuan
Visible, from the price point of view, C series also slightly lower.
Consideration: usually we choose the principle of circuit breaker is the rated current of the circuit breaker is greater than the load current, according to the nature of the load then choose C or D.
Type D is specifically designed for electrical type load, but this does not mean that type C circuit breaker cannot be used, but the calculation method needs to be adjusted.
We still need to explore the essence of learning, flexible grasp
III, the difference and application of miniature circuit breaker
1. For miniature circuit breakers, 1P+N, 1P and 2P are generally used as on-off control of single-phase electrical appliances
(1) Differences:
(2) Application:
1. In order to reduce the cost, 1P can be used, but the superior circuit breaker must have the function of leakage tripping. In maintenance, the superior power must be cut off to prevent accidents caused by fire line and zero line disorder;
2. In order to avoid 1 problem during maintenance, 1P+N can be used;
3. Reasons for using 2P: For the same 18mm module circuit breaker housing, the internal installation of 1P and 1P+N is different, the former in the state of short circuit accident "limit breaking ability" is higher than the latter, after all, space is an important factor affecting the breaking ability.
Therefore, for more important, maintenance and operation of frequent, prone to failure of the electrical circuit, it is better to use 2P (higher cost).
4. The premise of using 1P is that the lighting distribution box must have leakage trip function, at least the incoming line (or the upper level of the outgoing line) must use leakage circuit breaker.
5. 1P+N is perfectly acceptable for ordinary socket circuit, but not if you want to add leakage, because 1P+N circuit breakers cannot be assembled with leakage protection accessories and other electrical accessories.
2. Three phase generally divided into three kinds of circuit breakers, namely 3P, 3PN and 4P
(1) Differences:
3P: only for the pure three-phase electrical equipment, relative or phase short circuit trip, can not have single-phase load, otherwise a relative N line load, N line refluxing circuit breaker as leakage flow;
3PN: The four wiring L1L2L3N can use three-phase or single-phase electricity behind the transformer coil. No matter whether the three-phase load is balanced, the leakage switch does not operate.
Operate only when there is leakage, that is to say, when there is single-phase ground or inter-phase short circuit.
4P: The four wiring L1L2L3 pass through the transformer coil using the same method as 3PN, the difference is only 4P broken N line, 3P continuous N line.
(2) Classification method:
Quadrupole circuit breakers are classified into A, B, C and D:
A: N is not installed with overcurrent trip, and the N pole is always on, and does not combine with other three poles.
B: N is not equipped with an overcurrent trip, and the N pole is combined with the other three poles.
C: The N pole is fitted with an overcurrent trip, and the N pole is combined with the other three poles.
D: The N pole is installed with an overcurrent trip device, and the N pole is always on, not connected with the other three poles.
(3) Application:
1. In the case of using quadrupole, it must be noted which product is selected, because both quadrupole and overcurrent trip are installed on N line, and their functions and purposes are different.
N - line overcurrent trip is installed, it can be used in three - phase four - line distribution of single-phase load mainly in the line, or in a large number of harmonic generation nonlinear load such as gas discharge lamps, thyristor dimming, speed control circuits, or other occasions have special requirements.
General equipment circuit can choose N line circuit breaker without overcurrent trip.
2. In fact, although A and D are called quadrupole circuit breakers, their N poles are always on and do not combine with other three poles. Therefore, this type of MCCB is commonly known as "false quadrupole", namely 3P+N.
Therefore, this type of circuit breaker can only be suitable for use in three phase load but a small number of single-phase load occasions (such as control power use 220V complete system).
If the wrong choice, not only does not play a protective role, but will be a big problem, this is the most chaotic design and use of a problem, should cause attention.
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