When building or remodelling a building, be it a home or a business, you must plan how to distribute power within the structure. The most common way to deal with this problem is to originate all power circuits from the junction box that receives power from the electric company.
Power Distribution in Buildings
Older buildings use fuses to control and direct the power distribution. Modern houses and other types of facilities use junction boxes to serve the same purpose. All the circuits in the building begin at the junction box and travel throughout the building. The junction box contains a separate breaker for each circuit in the building. When a circuit in the building fails, the specific breaker within the box that controls the power on that circuit breaks the connection to the power source for that circuit without interrupting power to any of the other circuits in the building. When your needs for power have exceeded the available breakers in the breaker box, you can supply more power for more circuits in the building in one of two ways. You can either add another breaker or you can replace one of the existing breakers with a small format breaker that contains two separate switches, each one controlling one of the circuits in your house.
Purpose of a Breaker
The breaker performs the job of a switch to protect the circuits to which it supplies power. If there is a short circuit in the line, an excessive draw of current required or a person touches both powered and grounded lines the breaker pops and eliminates power on that particular circuit until you repair the problem that caused the breaker to pop.
Single Pole Versus Double Pole Breakers
The electric company supplies a building with three lines. One is neutral while the other two lines are 120V each with reference to the neutral line. When you use both of the lines carrying power in a circuit of the house, the voltage supplied is 240V. Most major appliances operate on 240V, such as the stove, furnace and hot water heater. To access both lines of power, the breaker in your breaker box must be a double pole breaker.
While double pole breakers connect to both power lines, single pole breakers only connect to one of the two available power lines. Most items in the building require 120V which originates from single pole breakers in the junction box. It is important to note that a single pole breaker connects to either of the two power lines but not to both.
Breaker Box Crowding
When you add new circuits to a building to supply new outlets to some part of the building, you must add a new breaker to the breaker box to control these outlets. Breakers control specific amounts of current, thus limiting the number of outlets that each breaker can include in its circuits. Breaker boxes have limited space and only have the ability to support a finite number of breakers. If the breaker box is full, you can add a new circuit by changing one of your current single pole single switch breakers for a single pole double switch breaker.
The double switch version of the breaker is the same size as the single switch version but it handles two separate and independent circuits, each with their own separate switch. Two completely different circuits within the building can run to the same breaker but operate entirely independently. If the breaker pops in one circuit the double switch breaker is supporting, the other circuit will not lose power.