Neutral wires that deliver balanced loads are not need to be counted. It should be noted that the minimum circuit size is #12 with a 20-amp CB. 2. With the exclusions indicated below, the maximum load on each circuit breaker is 80 percent of its rated for non-motor loads. Except for motors and a few other loads, a breaker cannot be greater than the ampacity of wire. Therefore, if you use 14/3 cable, each circuit must be no more than 49 amps.
Circuit breakers can be either magnetic or electronic. Electronic breakers use semiconductor components to determine whether or not to open the circuit. Magnetic breakers use a tripping mechanism that detects an abnormal current condition and automatically opens the circuit. The two types of magnetic breakers are contactors and motor starters. Contactors make electrical connection when they close the circuit, so they can't be used where absolute separation of power is required (such as in medical equipment). Motor starters are normally used with large appliances such as washers and dryers. They provide separate control of electricity to the motor and heat source, which allows these devices to be turned off even when they're plugged in. Motor starters also protect your equipment from damage if there's a power surge when you turn off the main line voltage.
The amount of current that a circuit breaker can handle depends on several factors, including type, size, weight, placement against a wall, etc. However, most circuit breakers can handle up to 100 amperes. Some circuit breakers are designed to handle much more than this value.
The circuit breaker size should be 125 percent of the ampacity of the cable and wire, or the circuit that has to be protected by the CB. Let's look at some solved examples: Assume a 20-amp lighting circuit with a 120V single-phase supply is wired using a 12 gauge wire. The conductor area of the cable must be at least 8 square inches for every foot it extends. The light fixture is rated for 1,200 watts so its motor must be able to conduct 1200 watts during each half cycle of the power source. Since the largest power rating on any part of the circuit is the light bulb, it follows that the circuit breaker must be sized at 20 amps. This means it can't be less than 15 amperes because that would put it below the minimum requirement.
The wiring method used on house circuits is called "split phase", which means that only one side of the circuit is used to carry current at any given time. If both sides of the circuit were loaded equally, then the load would need to be greater than 20 amps to require a 20 amp circuit breaker. However, since only one side of the circuit is loaded when lights are turned on, they use up only 10 amps of the available capacity. The other 10 amps remain for other loads such as heaters, air conditioners, and dishwashers that have motors that can use more than 10 amps at a time.
Each circuit breaker has a set amperage (amount of current). This rating is printed on the breaker. The majority of domestic circuits are rated at either 15 or 20 amps. That is, a 15-amp circuit breaker can handle approximately 12 amps, whereas a 20-amp circuit breaker can take approximately 16 amps. The exception is when you have several circuits that will be used for appliances that may use more than one circuit, such as a hot tub, heater, and air conditioner. In this case, you would want to get breakers that are rated for the total amount of current needed by all the appliances on the circuit. For example, if your house uses 10 amps of current through a hot tub and another 10 amps through a garage door opener, then you should get 20 amps of capacity in a single breaker. If the breaker fails to shut off when you expect it to, this could lead to burnout of the switch or even start a fire.
The number after the amp rating indicates the distance that the wire must be from any point inside the housing. So, if the breaker is located in the wall but the wiring remains outside the casing, there should be at least 18 inches between the breaker and the nearest electrical source. This ensures that enough space is provided so that electricity cannot flow through your body if you are accidentally touched by a live wire.
The wire size determines the breaker size. A 20 amp breaker should be installed on a 12 gauge line, and a 15 amp breaker should be installed on a 14 gauge wire. If you know the total wattage of the circuit, divide it by the circuit voltage to get the total amps of the circuit. Then add 25 percent more than that number to get the maximum load that can be connected to the circuit without requiring a larger breaker.
For example, if the total wattage of the circuit is 60 watts and it's a 120-volt circuit, then it will use 8 feet of 12 gauge wire. 60 watts / 120 volts = 5 amps. 8 feet of 12 gauge wire costs $0.89 per foot. So the cost of this wiring job is $95.52.
If two other houses also have 12 gauge wire on their circuits, then they too will have 5 amps going through them at all times. If one of those houses adds another light or appliance to its circuit that uses less than 10 amps, then its breaker will click over to the next size lower breaker automatically. For example, if the fourth house adds a television set that uses 7 amps instead of 10 amps, then its new breaker will be a 15 amp breaker instead of a 20 amp breaker.
So in this case, the cost of the work would be $95.52 plus the cost of the 15 amp breaker ($11.99).