Lighting circuits are wired in two ways: using junction boxes or with loop-in ceiling roses. The loop-in approach now predominates, while individual circuits sometimes combine the two for the most efficient use of cable. Lighting circuits, unlike power circuits, are usually radial in nature. This means that all the circuits feeding a single fixture run together toward that one point. They do not cross over each other's paths.
Junction boxes are used to house multiple cables entering a wall cavity from outside the building. These cables might be electrical wiring for lights, heat, air-conditioning, security systems, and so on. The box provides protection for the wires as they enter the structure and permits easy access to each circuit within. It also prevents contact with other electrically-powered components such as telephone lines or heating ducts that may be nearby.
The box should be located away from gas pipes and water meters to prevent any possible damage to these important utilities. Metal boxes are preferred because they provide additional insulation to protect against future damage caused by weather changes or aging structures. Wood is used instead when space is limited or the location is particularly hazardous; however, it does not provide the same level of protection as metal.
Wood boxes must be painted or stained to match any surrounding woodwork or siding and should be durable enough to withstand outdoor exposure. Plastic boxes are available but not recommended for use with electricity due to the possibility of leakage.
Circuits with loop-ins. The main circuit line from the consumer unit loops in and out of multi-terminal ceiling roses, from which individual cables flow to the light switches via loop-in wiring. This wiring arrangement eliminates the need for junction boxes and separate connections to the lights. Ceiling roses come in two varieties: single-pole and three-way. Single-pole roses have terminals for one light per branch, while three-way roses have branches for three lights per branch. The term "loop" refers to the fact that when you connect a cable to a terminal on such a device, it becomes part of the circuit through that terminal; therefore, if you want the light to work, you will also need to connect another cable to another terminal.
The proper term for this type of wiring is "subscriber wiring." It is required by law to provide safe wiring practices for electricity delivery purposes. If you're lucky enough to live in an area where your wiring is still inside the walls, then this type of wiring is called "commonsing." It's very important to properly terminate these cables or else you might end up with a short circuit down the road!
If you own a home with pre-existing wiring, then you should know that it is not legal to cut corners here.
A single pole switch and light fixture (switch at the end of the cable run) Use this pattern, sometimes known as a "switch loop," when it is more convenient to position a switch at the end of a cable run. In the final length, a 3-wire cable is utilized to provide a hot conductor in each direction. It necessitates the use of two-wire and three-wire wires. 6. Worked example: A lamp needs to be replaced in room 101. The old lamp is off the circuit but not removed. To determine if the circuit is complete, turn off all the lights in the hallway and look for an open wire or broken connection. If no open wires are found, then room 101 is still receiving power from the breaker that controls area 100.
The new lamp requires a 20-amp circuit. You need to know before you start work what type of wiring is used in the house. Single conductors with a ground wire attached is most commonly used for interior wiring. Three separate conductors with each carrying a different voltage is most often found in an exterior wall configuration. For both types of wiring, a black conductor is designated as "hot", a white conductor is "neutral", and a green conductor is "ground".
If you're working with three conductors inside the box, cut the third conductor to determine if the circuit is complete. If it's not needed any longer, simply leave it out. Otherwise, join the third conductor to the second one using a splice sleeve.
This is how it works. A constant current, variable voltage source is used in a series lighting circuit to deliver electrical energy to the loads connected to the circuit. This is in contrast to the more widespread usage of constant voltage, variable current circuits in everyday applications to deliver electrical energy. The term "constant current" means that the current through each light bulb is maintained at a constant value regardless of what resistance is placed in series with the power source. This is important because if the current were to drop too low, the lights would go out.
The basic concept behind series lighting is simple: if the voltage across two lamps is equal, then they will not flicker when lighted simultaneously from the same power source. For example, if you connect four 20-watt bulbs in series then each will have 10 watts attached to it. If you connect seven 50-watt bulbs in series then each will have 7 watts attached to it. You can see that there will be enough power available to all the bulbs in either case.
The problem comes in trying to make sure that the current through all the bulbs is about the same. If one bulb consumes more current than the others, it will heat up and fail prematurely. Also, if all the bulbs are not identical, then they will not have equal amounts of electricity flowing through them and some may glow very faintly or not at all.
A "Parallel Circuit" is made up of two loops, each connected to the battery and each with its own load. A voltage divider is a series circuit. Two light bulbs connected in series share the voltage of the battery: if the battery is 9V, each bulb receives 4.5 volts. This issue is avoided by using a parallel circuit. In this case, both loops are now connected to the battery, but they can have different loads because there are no connections between the wires inside the loops.
When you connect two things in parallel, all of them will receive the same amount of current unless one thing fails. For example, if you have 10 light bulbs in parallel with a resistor that reduces the current to each bulb by half, then all of the bulbs will still burn out at once if just one bulb burns out. But if you replace the failed bulb with a new one, the remaining nine will be able to shine as brightly as before.
In electronics, current always flows from high to low potential circuits. Therefore, all of the bulbs in a parallel circuit will burn out at once if one bulb breaks. However, if you replace the broken bulb with another new one, the remaining bulbs will be able to glow as before.