NEC, Article 250, "Grounding" notes that grounds also provide:

1. Voltage limitation in case of lightning, line surges, or unintentional contact with higher voltage lines

2. Stability of voltage to ground under normal operation

3. Facilitated overcurrent device operation in case of ground faults

4. A path to conductive objects that will limit the voltage to ground.

In R&D work there is one additional function for grounds: a common reference plane or system ground return for electronic devices, circuits, and systems. (See Section 9.3) It is recognized that such grounds are essential in some cases to control:

1. Noise associated with the primary power system:

a. Incoming on the line

b. Outgoing from local equipment

2. Ground wire noise

3. Circuit coupling

a. Ground loop (shared circuit return)

b. Magnetic, capacitive, or electro-magnetic.

If system return impedances are low enough, then simple radio-frequency chokes can be used to limit this noise with no effect on the safety function.

A 50-microhenry choke will add 1/50 of an ohm at 60 Hz, but will look like 2 ohms at 7.5 kHz and 30 ohms at 100 kHz. Such an RF choke will serve to discriminate against noise on the ground circuit.

An inexpensive RF choke may be installed in the safety ground by:

1. Pulling the green ground wire 20 feet longer than required.

2. Coiling the extra length on a 6-inch diameter (about 12 turns).

3. Securing it tightly wound with cable ties.

4. Connecting it into the circuit.

These actions satisfy the NEC requirement for a continuous ground and noise isolation is also enhanced.

Whatever scheme is used, the ground of experimental equipment shall be connected to the same ground as the facilities' electrical system to ensure equal potential.

For practices involving hazardous materials, such as explosives, the grounding shall also comply with the requirements of Section 5.0, "Special Occupancies".