What’s the difference between negative and ground in circuits?
In: Engineering
Negative returns to the power source to complete the circuit, ground literally goes to the ground.
To imagine it most simply, say you have a battery with positive and negative ends right? And a light bulb to turn on. You need to run one wire from the positive end of the battery to the light bulb, then you need to run another wire from the light bulb back to the battery to complete the circuit. With this the circuit can function normally. The ground wire is then a totally separate wire. It’s job is to dispel electrical energy in the event that there is an electrical build up or a short circuit or any other event that could possibly shock a person or start a fire.
Negative/neutral is the correct path for electricity to flow back and complete the circuit. Ground is the spare path in case something goes wrong – usually helps prevent people from dying.
Negative is just the opposite side to a power source from positive.
Depending on the context, ground can mean several things. In automotive terms, and many other vehicles, the whole chassis is a conductor. It is used for the negative side to reduce wiring. Only the positive side needs wiring, the negative side is just grounded to the chassis. Some older vehicles do have reverse polarity meaning the positive is ground and negative needs the wiring.
In housing and other real estate there is no positive or negative because it’s alternating current. The ground is a safety device to make sure electricity has a safe path in case of a short or static buildup.
With the rise of transistors, negative became the near universal “common” side of circuits, returning current back to the DC source. To mitigate capacitive effects with what is usually a metal chassis, this leg is also connected to the chassis to dissipate charge build up.
Because the connection to the chassis acts in a largely equivalent nature to why mains AC is connected to earth – dissipating excess charge from capacitance – “grounding” with the chassis in DC circuits is colloquial but not exactly inaccurate, despite these connections not usually being connected to the actual Earth. There are technically more official terms, but anyone in industry understands them perhaps excepting official and complex documentation.
The terminology is different between Direct Current and Alternating Current. DC circuits have a positive and a negative. AC circuits have a hot and a neutral (for 110v or hot hot on opposite phases for 220v). Both kinds of circuits can have a ground which more often than not eventually end up in the same place as the negative or neutral.
“Ground” is a common reference in a circuit, the “zero”, to which all other electrical potentials on that circuit are compared. It just so happens that in a lot of electrical systems it’s literally the ground, because it’s really difficult to do anything to change it’s potential even if you dump a bunch of charge into it, and so it’s a stable reference. But in the car it’ll be the chassis, etc. It serves the double purpose as a safety measure by making sure there’s no charge building up anywhere (because everything is connected to everything else), because that charge suddenly shorting (say, if you touch it) could hurt you or the device.
It’s just a really common convention to connect the negative terminal to ground. But you could connect all the positives. It doesn’t matter as long as you’re consistent in your circuit.
It depends on the context. In cars, boats and aircraft (small boats and aircraft), ground is basically a path to the negative battery terminal. So effectively ground and negative are the same thing.
In the AC world it’s a bit different.
In electronics, “ground” is a somewhat ambiguous term, since it has multiple meanings that depend upon the situation. It can be a little confusing.
One of the uses of “ground” is in safety ground or earth ground. That’s what the third prong (in the USA) of some plugs are. They literally are connected eventually to the ground. Usually the chassis or case of a device is hooked up to earth ground, so that if there’s a short circuit it will channel current to the earth rather than a user. This also helps avoid unwanted emission of radiation.
More often, “ground” simply refers to a common point in a circuit that is considered the 0 volt reference point. It isn’t necessarily truly at 0 volts but that doesn’t matter since voltages are always relative to each other. If a system is self-contained, it doesn’t matter if the ground is not really 0 volts (the same potential as the Earth).
In many circuits, all of the voltages are positive. So the ground is connected to the negative terminal of the battery or power supply, and the circuit’s “power” comes from the positive terminal.
There are circuits that use both positive and negative voltages (such as many operational amplifiers). In those cases, there are 3 (or more) power supply voltages available…positive, negative, and ground.
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