In electronics, the term "
ground" is misused by even some
technicians. A ground is any point where a signal is
referenced. You may, for example, measure a voltage differential between a
wire in a
circuit with 100 volts and one with 300 volts. The voltage between the lines is 200 volts, with the first line as the referenced ground.
That being said, there are several different types of commonly-referenced grounds.
- Earth Ground: Uses the theoretical absolute ground of the earths surface. Your house wiring uses the earth ground; the wiring bringing in electricity is only 1/2 of the circuit.
- Signal Ground: Uses an actual wire or circuit for the return path. Battery-powered devices use signal grounds.
- Chassis Ground: Also called protective ground. The chassis of a device may be tied to earth ground, but when taking electronic measurements one uses the chassis of the device as the reference. Your computer repair technician uses the chassis for the black lead of his multimeter to read voltages, etc. Should something break in your computer power supply, for example, the case would not become 'hot' and electrocute you. Some technicians consider the chassis ground to be an extention of the earth ground.
Having a proper ground will help to avoid electrocution, which is a good thing. It also helps to reduce Electromagnetic Interference, or EMI. Your computer has an oscillator that runs into the high MegaHertz range. This acts like a miniature transmitter. If your system is not grounded properly, you can generate this interference, which can disrupt your monitor or any radio equipment you have near the computer. Properly grounding and shielding a computer is particularly important for ham radio operators because they deal with listening for weak signals, and having a loud buzzing noise can cover up what they are listening for. Your computer, and most every electronic device for that matter, carries an FCC warning and certification. Each electronic device is type tested for EMI and certified as non-interfering.