Grounding is essential to ensuring the safety and reliability of electronic equipment. To ensure low impedance, ground lines are usually thick cables securely connected to a ground. However, the specifications for ground lines cover DC resistance only; a DC resistance of 10 Ω or less for a type-A ground and a DC resistance of 100 Ω or less for a type-D ground. The specifications do not address high-frequency impedance at all. Nevertheless, in a typical semiconductor plant, ground lines are generally located in cable racks together with the power lines, and power and ground lines run side-by-side over long distances. If we assume, for example, a ground line 100 meters in length in a cable rack 2 meters above the floor, its impedance will be 14.4 Ω at 10 kHz, 106.4 Ω at 100 kHz, and 862 Ω at 500 kHz. Put simply, the impedance becomes high at the higher frequencies.

This is another reason why ground lines (both those attached to grounds and those attached to cables) are susceptible to electromagnetically induced currents, a common source of noise.

Such ground line noise can cause serious problems for electronic equipment. However, since the safety and protection function of grounding is the first priority, conventional noise filters (such as inductors) are not suitable for preventing noise. As a result, some users try to make do with measures aimed at reducing noise around the power lines or changing the routing of cables, while others take the extreme step of disconnecting the ground line altogether.
Problems caused by ground line noise often have characteristics such as the following.
Problems are not constant but occur suddenly and unexpectedly.
Problems are not very reproducts and do not occur with consistent frequency. (Depending on conditions, they may occur once every few days or even months.)
Problems are not limited to the area in physical proximity to the equipment generating the noise. The cause of a particular problem may actually be located far from the equipment it affects, though somewhere within the same building and along the path of the ground line.
Due to differences in the noise environment, in many cases problems do not occur at the manufacturer's site, becoming apparent only after the equipment has been delivered to the customer.