Section 250.4(A)(1) of the National Electrical Code (NEC) states that the electrical system is connected to ground to limit voltage imposed from lightning strikes, line surges, high-voltage crossovers and to stabilize voltage-to-ground under normal operation.
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The equipment is then connected to the system to limit voltage-to-ground at the equipment. This is done through a branch circuit conductor that extends the connection from the equipment to the “Grounding Electrode Conductor”, back at either the service or the source of a separately derived system. This ensures control of the voltage to prevent physical damage to electrical equipment.
NEC requires that, where available on the premises at each building or structure served, all grounding electrodes including “made” electrodes be bonded together to form the “Grounding Electrode System”.
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The “Grounding Electrode System” includes metal underground water pipes, metal frames of buildings, concrete-encased electrodes and ground rings.
The general requirement is that a bonding jumper must be installed between the grounding electrodes to bond them together.
The requirements of NEC Section 250.2 states that an effective ground fault current path is an intentionally constructed, permanent, low impedance, electrically conductive path designed and intended to carry current under a ground fault conditions from the point of a ground fault (like an overcurrent device) on a wiring system to the electrical supply source and that facilitated the operation of the overcurrent protective device. This is the function of a “Bonding Conductor” and not the function of a “Grounding Electrode Conductor”.
With that assumption, and based on that incorrect interpretation, many electricians assume that in a properly functioning electrical system, currents in grounding electrode conductors are only present during faults, and only for a very short time.
Although further examination of 250.4 (A)(5) should make it clear that the earth shall not be considered an effective ground fault current path, misconceptions still persists.