18 Key Terms Defined In NEC System Grounding Requirements

System Grounding Arrangement

The topic of system grounding is extremely important, as it affects the susceptibility of the system to voltage transients, determines the types of loads the system can accommodate, and helps to determine the system protection requirements.
The system grounding arrangement is determined by the grounding of the power source. For commercial and industrial systems, the types of power sources generally fall into four broad categories:

1. Utility Service – The system grounding is usually determined by the secondary winding configuration of the upstream utility substation transformer.
2. Generator – The system grounding is determined by the stator winding configuration.
3. Transformer – The system grounding on the system fed by the transformer is determined by the transformer secondary winding configuration.
4. Static Power Converter – For devices such as rectifiers and inverters, the system grounding is determined by the grounding of the output stage of the converter.

Categories 1 to 4 fall under the NEC definition for a “separately-derived system”. The recognition of a separately-derived system is important when applying NEC requirements to system grounding. The National Electrical Code does place constraints on system grounding.

As a starting point, 18 key terms from the NEC need to be defined:

1. Ground

A conducting connection, whether intentional or accidental, between an electrical circuit or equipment and the earth or to some body that serves in place of the earth.

Ground definition (photo credit: ibiblio.org)

2. Grounded

Connected to earth or to some body that serves in place of the earth.

3. Effectively Grounded

Intentionally connected to earth through a ground connection or connections of sufficiently low impedance and having sufficient current-carrying capacity to prevent the buildup of voltages that may result in undue hazards to connected equipment or to persons.

4. Grounded Conductor

A system or circuit conductor that is intentionally grounded.

Grounding simple scheme (photo credit: diy.stackexchange.com)

5. Solidly Grounded

Connected to ground without inserting any resistor or impedance device.

6. Grounding Conductor

A conductor used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or electrodes.

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