So I bought a motorcycle that doesn’t work, and I’m trying to fix it up. I’m pretty new to electrical work, and having trouble with the concept of the ground. On my bike, the electrical components are grounded to the steel frame, and the negative battery terminal is also grounded to the frame.. so is the frame basically a conductor back to the negative terminal? Why is it not dangerous to be exposed like that unlike the insulated wires??
In general the concept of ground is a little hazy for me.
Thanks
In: Physics
Ground is a common concept used from the tiniest of electrical circuits to electrical grids. Let’s stick to the motorcycle’s electrical system to look into it. Ground is one section of the whole installation that is (for practical purposes) all at the same voltage and is set as a reference point. In an absolute majority of cases, the negative terminal of the battery is connected to ground. Also connected to ground is all the electrical equipment: lights, horn, starter, instrument cluster, etc. When you turn on the headlight, (simplified) you basically close a path from the battery’s +12V to one side of the lamp, while the other side is at ground -> you now have 12V across the bulb, the intended current flows from the + of the battery through the bulb back into the – of the battery. Now, you could run a wire from every single electrical component to the negative terminal, or have some sort of tree structure. Since you already have a conductive piece of metal spanning across most of the vehicle, it is however convenient to use just that. So all the bulbs in the rear light assembly may just have their negative on a common metal baseplate, which is in turn screwed to the frame, or connected to it through a couple of inches of wire. This basically cuts the amount of wire needed in half and one can measure pretty much any voltage referencing it (aka holding the black probe to) an exposed part of the chassis. Yes, the frame is the return path for the current in this scenario. It’s not dangerous because the battery’s internals “work” to create a voltage difference of 12V across the terminals, not to establish any kind of potential difference between the chassis you’re touching and the garage floor you’re standing on. The Cables are insulated because copper is sensitive to corrosion and because no other voltages should touch each other or ground. There are generally fuses to prevent anything too bad from happening, but it can still damage stuff or cause unfunny sparks.
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