Multiply the number of electrical windings or other components by the voltage they provide. For example, if you want to calculate the breaking capacity of a three-phase 520-volt transformer, multiply 3 by 520, which is 1,560 volts. Divide this voltage by the volt-amperage flowing through the circuit. In this case, divide 1,560 by 120, which equals 14 amp-hours.
The next step is to add the amp hours for each component in the circuit breaker. For this example, let's say that the breaker also provides some type of fault protection. Therefore, it must be able to open both conductors at once in order to break the power. The ampere hour calculation would be the same as above but with two 140-amp hours instead of one. Add these together and divide by 10,000 to get the AIC rating. In this case, the total ampere hour rating is 28 amp-hours.
There are two main types of circuit breakers: magnetic and thermal. Magnetic breakers use the current strength to generate a magnetic field that opens a set of contacts inside the breaker. This type of breaker can handle up to 20 amps or 20,000 milliamperes. Thermal breakers use the heat generated by the current flow through a resistor to destroy a fragile member inside the breaker. These breakers can handle 100 amps or more.
In the case of three-phase loads, divide the VA by the nominal voltage and the square root of three (approximately 1.732). What size breaker do you need if your total 3-phase load in a 480V system is 50,000VA? 60.2-ampere-hours = 50,000-volt-ampere-hours (480V x 1.732). Therefore the required breaking capacity is approximately 75 A or 90 A depending on whether you want to be over or under sized.
As long as the total current drawn by all three phases is less than the rating of the breaker, then there will be no problem with overloads on any one phase causing damage to other parts of the distribution system or to those devices attached to it. The only time this could cause problems would be if the overloaded phase was also carrying current from another source. For example, if a single 240-volt, 15-amp circuit were to cause an 80-percent-capacity breaker to open, that circuit would be damaged even though its current remains well within its limits. The reason for this is that another phase of the system is now drawing the full amount of current through that same cable which may not have been able to handle it before. This is called "cross-connection" and means that part of the distribution network is now operating outside of its designed parameters. This can lead to failure of connected equipment or worse yet, fire.
Cross-connection can occur in several ways.
How to Determine the Size of a Circuit Breaker Required for a Machine: Horse Power of the main motor is 220 volts, 1 phase is 220 volts, 3 phase is 440 volts, and 3 phase is 1 horsepower.
I F.L = P/1.73 * V L-L, where P is the transformer power rating in VA and V L-L is the secondary side's line-to-line RMS voltage. The I F.L is 1,000,000/1.73*480 = 1,202 A; the I F.L is the transformer's full load current. This example shows that if a transformer were to fail because of a short circuit, it could draw its full load of 1,202 A from the source.
The breaker should be large enough to handle the full load of the transformer with no problems. If it weren't, the transformer would get damaged. The full load capacity of a breaker can be found in its name: breakers are designed to open when the current they're carrying reaches the full value allowed by law. For example, the breaker on a 20 AMP circuit must be able to carry 200 AMP (20 A for 20 minutes). A 40 AMP circuit would need a 60 AMP breaker. A 60 AMP circuit could be 100 AMP or more if there were several other circuits also loaded with 20 AMP or less. Transformers don't like high currents for long periods of time so this should give you an idea of how much power your whole system requires.
Transformer windings and core material will also determine how much current a short circuit can draw for a given amount of power. The bigger the transformer, the more current it can handle before damage occurs.
The greatest voltage that may be applied across all end ports, the distribution type, and how the circuit breaker is directly incorporated into the system all contribute to the total voltage rating. It is critical to choose a circuit breaker with sufficient voltage capability to match the final application. For example, if you plan to run three-wire appliances such as heaters, air conditioners, or pool pumps on this circuit, then you will need a breaker capable of handling their maximum load. Circuit breakers are available with maximum current ratings from 20 amperes (20 A) to 100 amperes (100 A). The higher the maximum current capacity, the more expensive the breaker will be. Don't forget about the number of circuits you will have in your installation. If you plan to use these circuits to power several appliances that will be switched on at once, such as four-season jackets, space heaters, and air conditioners, then you should select a breaker with a high enough maximum current capacity to handle all those loads simultaneously.
The next factor to consider is the amount of overcurrent protection required by each circuit. Overcurrent protection can be accomplished by using fuses or circuit breakers. Fuses are designed to blow open when they reach their "limit of endurance" which is usually specified by the manufacturer as being able to withstand only a certain amount of continuous current flow. Once the fuse blows, it is useless for its intended purpose and must be replaced.
Concerning the main side,
This formula is sometimes written as W=A X V. For instance, if the current is 3 amps (3A) and the voltage is 110V, multiply 3 by 110 to obtain 330W. (watts). P = 3A X 110V = 330 W is the formula (with P standing for power). This is why watts are sometimes referred to as volt-amps. The amps are frequently inscribed on the handles of circuit breakers.
The basic structure of a circuit breaker is a mechanical switch connected to an electrical conductor and controlled by an operating mechanism designed to open the switch when actuated. Circuit breakers can be divided into three main types: ground-fault circuit interrupters (GFCIs), line-commutated circuit interrupters (LCCIs), and contactors. Contactors are simple devices that use magnetic forces to close and open contacts inside of them. They are used for low amperage applications such as lighting and small appliances. LCCIs combine the functionality of GFCIs and contactors. They use magnetic forces to close their contacts and also employ electronic components to make sure that they remain closed. Thus, they provide both protection against ground faults and line-to-line voltage differences. Finally, GFCIs add another element to prevent damage to equipment caused by high currents flowing through conductors that are not grounded.
Each type of circuit breaker has its advantages and disadvantages. For example, LCCIs are more efficient than contactors, which are more efficient than GFCIs.