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How to choose the wire

release time:

2021-09-15

1. The safe cut-off of the wire

In our actual wiring work, the mutual substitution of wires is a common situation. When we judge whether two wires with different cross-sectional areas and materials can be substituted for each other, the first thing to think about is the problem of safe interception. So what is safe interception of traffic? In layman's terms, it is to prevent the wire from causing serious heat generation and relatively large voltage loss due to excessive current when the wire is in use. At this time, the current value passed must be limited to a reasonable range. This is limited. The highest current value is called the safe cut-off flow. Since the calculation of the safety cutoff is a bit cumbersome, it is related to the material of the wire, the type of wire, the wiring method and the ambient temperature used. Sometimes time is tight when wiring, and there is usually no time to carefully calculate the task. We solve it. The basic method is to estimate by formula.

2, empirical formulas to estimate the safe interception of wires

Below we use aluminum wires to estimate the relationship between the interception capacity and the cross section:

" 10 under five, 100 on two, 25, 35, four and three circles, 70, 95, two and a half times.

Wear tube, temperature, 20% off.

Add half of the bare wire.

Copper wire upgrade calculation. "

Now let’s explain this formula. The first sentence of the formula is to point out that the safe cut-off of aluminum wire is calculated as a multiple of the cross-sectional area. We know that the cross-sectional area of wires is expressed in square millimeters. The cross-sectional areas of commonly used wires in China are 1, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185 and so on. The "10 under five" refers to the wire in the range of 1 square millimeter to 10 square millimeters. We multiply the area of this wire by a multiple of 5 to get the safe cut-off amount of the wire. For example, the 6 square aluminum wire mentioned in the title, its safe cut-off capacity is about: 5X6=30A.

The second part: "25, 35, four and three circles", this sentence means that the cross-sectional area of the aluminum wire of 25 square millimeters and the aluminum wire of 35 square millimeters are the dividing lines multiplied by multiples. When the wire is 25 , We multiply by a multiple of 4. For example, aluminum wires of 16 square millimeters and 25 square millimeters should be multiplied by 4; aluminum wires of 35 square millimeters and 50 square millimeters should be multiplied by 3.

The third part: "70, 95, two and a half times" means that for 70 and 95 square millimeters of aluminum wire their cut-off flow is multiplied by a multiple of 2.5. For example, for 70 square millimeters of aluminum wire, we use 70X2.5=175A .

The second sentence: "Through the pipe, temperature, 80% to 90% off", this sentence means that when the wire is routed, if the insulating sleeve is taken into account, it must be multiplied by 0.8 on the basis of the above calculation. If the temperature around the wire exceeds 25 degrees, then multiply it by 0.8 and then multiply by 0.9.

The third sentence: "Bare wire plus half", this sentence means that if the aluminum wire is wired outdoors, the current can be calculated by adding half

The fourth sentence: "Copper wire upgrade calculation" means that if copper wire is used for wiring, we can use the above formula to calculate the cut-off capacity of one wire number larger than aluminum wire. For example, we can calculate the copper wire of 2.5 square millimeters according to the aluminum wire of 4 square millimeters. In this way, we can get the safe cut-off capacity of 2.5 square millimeters of copper wire is 4X5=20A.