Speaking of the wires on the wiring harness, we must first classify them. Otherwise, it is wrong to generalize. From the function point of view:
1. Power cord;
2. Ground wire;
3. Signal line;
It can be roughly divided into these three categories. Please note that the wires mentioned in this article refer to
traditional cables, excluding USB, Fakra,
HSD,
HDMI, and other high-frequency special wires, because this part is not necessary for you to choose, and general
wiring harness manufacturers can't do it. Most of them are used and buried in the middle of our
wire harness.
2
power cable
There are two types of power cords:
(1) There are fuses upstream
Most of our power cords are located downstream of the fuse; that is to say, a fuse protects them, so the choice of this type of power cord is: it must match the fuse upstream of it. (Please note that it is upstream, not indirect). So, you see the critical point: choose the fuse first, then the wire. This is beyond doubt.
Also, in principle, the wire diameters of all wires downstream of the same fuse should be the same, even if some only use the power supply as a signal (such as the ACC and IG wake-up of some modules). Of course, if you are a master, you know that it can be inconsistent. This has a premise; you have to see the principle; this principle cannot be "used in this way before, no problem"). When your skill hasn't reached the heat, keep the same so that there are fewer mistakes.
As for matching the wire with the fuse, if we must talk about it, the essential point is to ensure that the fuse can protect the wire when a "fault" occurs.
When many people discuss here, they consistently mention a concept-"smoke temperature". This concept has "poisoned" many people. I won't talk about the origin of this concept, but one sure thing is that we cannot use this concept in our design. Why? It's smoking, how far is your car from burning? ! What's even more ridiculous is that the current source of people has abandoned (abolished) this concept, but we are still spreading it. Why is it canceled? Everyone can think about it.
The matching relationship between the fuse and the wire, to be honest, I can't tell you here, use it, because this is a "know-how" in every company, and it is suspected of leaking.
(For the time being, let's give a small example. For example, everyone knows that 0.5 wire is generally used to match 10A mini insurance. If 15A is suitable, 20A is exemplary? If you say no, then you still have not mastered the matching principle. Of course, dogmatic "knowledge" tells you that it won't work. This is where the wiring harness system is fun and flexible.)
But on the other hand, you can choose first, go to match, and finally check with CPT (Cycle Protection Test), go to the bottom, pass the test, and you will always get an optimized solution---so, Don't think of system testing as a laboratory thing. System engineers must understand it well and make good use of this tool. You will find a reasonable balance between quality and cost. Otherwise, it isn't easy to design. --A system engineer who does not understand system testing is not a qualified harness designer.
(2) There is no fuse upstream
There are still very few such wires in the car, only a handful of them. Generally speaking, their choice is based on the requirements of the electrical system, usually resistance/voltage drop.
3
Ground wire
Ground wire, generally speaking, the choice of wire diameter is based on the load current. This type is simple, so sometimes you will find the same electrical device, power supply, and ground wire. However, working The time currently is the same, but it can be different because selection is different.
There is also a type of ground wire, which is also used to match the upper fuse of the electrical device. In this case, it must be the same as the power wire.
4
Signal line
Ground wire, generally speaking, the choice of wire diameter is based on the load current. This type is simple, so sometimes you will find that the same electrical device, its power supply, and ground wire. However, working The time currently is the same, but it can be different because the basis of selection is different.
There is also a type of ground wire, which is also used to match the upper fuse of the electrical device. In this case, it must be the same as the power wire.
5
So if these principles are used well, what are the benefits?
To
In the past, we had an unwritten requirement that on the
wiring harness of the whole vehicle (passenger car), the wires of 0.5 and below should account for more than half of the total number of circuits. Otherwise, it would not be a good design.