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The neutral is a current-carrying conductor. The only differences between the neutral and the supply (or "hot") conductor is that each is marked differently, the supply conductor is run through a circuit breaker, and the wires carry current and voltage out of phase by 180°. They both conduct the same current, and are treated alike within a facility. They are run parallel to each other, and each is isolated from the other and from ground. Inside the facility, both hot and neutral conductors are designed to float, or pass through, without grounding or bonding to enclosures like conduit boxes, device boxes, ISBPs and sub-panels. In this manner, the neutral conductor is isolated within the facility. This isolation is important throughout the facility downstream from the supply side of the electrical power service entrance, or ESE.
Much, if not most, of the danger posed by stray currents and electromagnetic fields at a facility can be attributed to an electrical neutral conductor that has been bonded to the grounding system somewhere inside the facility near the occupants and downstream from the ESE. Such an action would be in violation of NEC Article 384-20 (1999) and / or a municipal or state law.
If this were to happen to a "hot" conductor, it would likely trip a circuit breaker and be corrected on the spot by any electrical worker. Isolating a "hot" conductor is routinely done to get power where it needs to go, to prevent the danger of electrical shock and fire, and to correct shorts and "ground faults." All of these reasons apply to the neutral conductor as well, but many electrical workers treat the neutral conductor as just another ground instead of as the "hot" conductor. This results in many unorthodox and hazardous wiring configurations at power outlets, junction boxes, and sub-panels, which take time to find and repair.
It is too critical to keep power supply wires balanced for life safety. Balancing prevents overheating, fire, and electrical shock, as well as premature breakdown of the electrical system. Keeping the voltage balanced between hot and neutral conductors also eliminates stray electromagnetic fields, making the interior of the facility "quiet."
No electrical power neutral should be permitted an alternate pathway to ground on the load side of the ESE. This means that the entire length of the neutral conductor, to include splices and bus bars, must be kept isolated all the way to the supply side of the ESE. This should be done in equivalent manner as isolating the hot supply wire pathway. Always run the neutral and hot conductors in parallel, float them in enclosures, and provide a separate grounding wire.
Only at the supply side of the ESE should a sole connection between ground and neutral be made. Only at this same point can a neutral-to-ground pathway be formed at a facility. This is the point that fulfills the description of the neutral as a "grounded conductor" at the facility. Further discussion on neutral grounding outside of facilities can be found in the page entitled "How Current Flows."
No electrical power neutral should be connected to ground in any ISBP.
Likewise, if an electrical outlet is desired to be installed in close proximity to or built at the ISBP, it must be installed with isolated neutral and isolated hot, and with its ground directly connected to the electrical power service module of the ISBP. The isolated neutral and hot wires would have to follow the GEC path back from outdoors to the ESE for connection on the load side of the service.
Not even in an ISBP can a connection or pathway be made between neutral and ground. Keeping an isolated neutral on the load side of the ESE is at least as important as having an ISBP. Only on the supply side at the ESE should such a connection between ground and neutral be made.
A grounded neutral downstream from the ESE is dangerous; it will work against the facility and against the ISBP by endangering facility occupants unneccesarily and by weakening the electrical grounding system prematurely inside the facility. Within facilities receiving electrical supply service, an isolated neutral downstream from the ESE can prevent and mitigate the problems associated with the improperly grounded neutral conductor.
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