In home decoration, it is often encountered that it is necessary to choose the size of the wire, the wire is not cost-effective, and the choice is small and easy to heat up and even cause the wire to catch fire. So how to choose the size of the wire?Let's take a 2200-watt water heater as an example to see how big the wires should be
Actual current calculations.
Whether it is to select wires for the water heater or wiring in a workshop, the cross-sectional area is selected according to the actual current of the line, so we must first calculate the current size according to the power.
For a single device, we can calculate the actual current based on the power of the individual device;If there are multiple electrical devices, in addition to adding up the power of these devices, we also need to consider the sharing factor, that is, the proportion of these devices used at the same time.
For example, if all of these devices will be used at the same time, then the sharing coefficient will be taken as 1;For example, if only half of these devices are used at the same time, then the sharing coefficient is 05；And so on. Now let's calculate the rated current of a single-phase 220v 2200 watt water heater: i = 2200 220v = 10a.
The cross-sectional area is selected according to the magnitude of the current.
According to the current to select the cross-sectional area, generally we can use the wiring formula or the current carrying capacity ** to calculate. There are two common formulas for estimating the current carrying capacity, the first one is simpler than the second, but the error is relatively large.
Formula 1:
"Ten under five, one hundred on two, two five three five fifty four three realms, seven zero nine five two and a half times, the temperature ** fold".Mantra 2:
"Multiply two by nine and go up by one. Thirty-five times 3.5, double in a group minus five. The conditions have been changed and converted, and the high-temperature nine-fold copper has been upgraded. The number of pipe roots is two, three, four, eight, seven and six folds full of current. ”The wiring formula is convenient and fast, but the error is large;The line selection results by the current carrying capacity** are more accurate, but relatively cumbersome.
According to formula 1, 15 square copper wire, open wire installation, the safe current carrying capacity at room temperature is about 20a;The current carrying capacity of 2 pipes is discounted on the basis of open wire installation, that is, 20*08=16a。
Then let's take a look at the wire ampacity meter:
From **, it can be seen that 1The ampacity of the open wire of 5 square copper wire is 21a, and the ampazacity of 2 pipes is 14a, which is not much different from the estimated results.
Summary.
From the above analysis, it can be seen that 1The current carrying capacity of 5 square copper wires, whether through pipes or open wires, is much greater than the rated current of 10A of the water heater, so the single core is 15 square copper wires can fully load a 2200 watt electric water heater.
This is why the 2200 watt electric water heater uses a 10A rated current plug, and the power cord generally uses 1 square copper wire.
Note: According to the home improvement design standard, the cross-sectional area of the power cord of the home socket shall not be less than 25 square copper wires. That is to say, if you want to install a socket at home, no matter what electrical equipment you plug into this socket, the minimum socket line is 25 square copper wires. In addition, the air-open leakage switch can protect the wire from overload and burning, so the reasonable choice of the air-open is very important for the wire, otherwise no matter how large the wire may be burned.