Household circuit breaker selection and distribution

August 6, 2019

When we chooseHousehold circuit breaker , or make an indoor distribution box, the first difficulty is the distribution of the loop: divided into several loops? Do you RCD? What kind of circuit breaker? Today, we will talk about the choice and distribution of household open space for indoor distribution boxes.

The first step, the sub-loop divides the circuit well, is the basis for selecting the breaker of all breaker, according to the circuit in which it is located.

In general, the basis of the number of loops in the distribution box is related to the number of rooms. For example, three rooms, two halls, one kitchen and two bathrooms, a total of 8 rooms, we need 8+1 mcb - 1 lighting circuit, and 8 socket circuits. If there is a smaller room, such as a small restaurant, connected to the living room, you can cancel a loop.

In addition, a separate loop is added to the number of base loops—the number of high-power appliances in the room is calculated, and each high-power appliance uses a separate loop. Which are high-power appliances? Look at its plug, any need to use 16A three-hole socket, are considered high-power appliances.

In general, the high-power appliances that appear in the home are only air conditioners and electric water heaters. At this time, we add 5 high-power electrical circuits - a total of 1 + 8 + 5 = 14 loops, plus a main switch, a total of 15 mcb.

The second step, the selection function, all the air has two functions - overload protection and short circuit protection, this is the basic function, we do not need to choose. The selection function, in fact, is to select accessories - different circuit breaker accessories, which can provide different protection functions. There are only two types of accessories for household use: leakage protector accessories and over-voltage protector accessories.

Leakage protector accessories are installed in a regular manner and must be installed on all outlet circuits - the above 15 empty openings require the use of leakage protectors on 8 outlet circuits and 5 high-power electrical circuits. A total of 13 are required.

Over-voltage protection can be optional, of course, it will be better - can protect the electrical appliances, especially in the period when the house has just been delivered, debugging circuits can effectively protect the electrical appliances from being burned. The overvoltage and undervoltage protectors can only be mounted on the main switch - there are two types of overvoltage and undervoltage protectors, one for manual closing and one for self-resetting. The latter is recommended for use in the home. It will be used in a lot of ways. More importantly, it is not possible to supply power in time after the power outage.

The third step, estimating the current estimation current is a technical task, and is also a crucial step in the open selection. The current here refers to the total current in each loop. For example, in the bedroom outlet circuit, it is necessary to calculate the sum of the currents of the appliances that will be used on all the outlets.

The electric power formula can be used for estimation: P = UI, current = power / voltage (220). For example, a kettle with a power of 1000W has an operating current of 1000/220=4.5A. In general, the normal socket circuit in the room will not exceed 20A, the kitchen may be a little more, but generally it will not exceed 25A. The maximum current of the appliance with independent socket circuit will not exceed 25A. Tip: This algorithm can only be estimated, not accurate. For example, some electrical appliances with motors will generate a large current when starting. So on top of the calculated results, choose a larger parameter.

The air-opening selection cannot be blindly selected. It needs to match the line current and the rated current of the socket to avoid the line overload but the air opening does not trip. It is also not optional, otherwise the line is not overloaded, and the air has tripped. This is called "misoperation".

The fourth step, the number of poles can be explained here, why the total current of the ordinary socket circuit and the total current of the independent socket circuit are both 25A, but to make a separate circuit for high-power appliances? This is because the operating current of a single electric appliance of a high-power electric appliance is large, and whether it is activated or not has a great influence on the selection of the open-opening--this is the preferential treatment of the high-power electric appliance.

In addition, high-power appliances have another advantage, that is, the number of circuit breaker poles. In the home circuit, only the 2P circuit breaker can provide protection for both the zero line and the live line. Therefore, in this single-electric, high-current circuit, a 2P circuit breaker is required - of course, the main switch must also use a 2P circuit breaker.

In addition to these two kinds of circuit breakers, 1P open or 1P+N open can be used - 1P open must be used with the neutral line, and the zero line cannot be disconnected when disconnected. Therefore, it is recommended to use 1P+N to open.