![]() ![]() ![]() ![]() Supposedly, the NEMA 5-l5R socket maintains the polarity of the building wiring, with the wide blade being the neutral conductor. INLINE FUSE CODEFor this reason, a fuse in the neutral must be prohibited, or it must be “ganged” with the phase conductor fuses such that if any one, including the neutral, operates, they all open.įor single-phase plug-and-socket-connected equipment, the plug and socket may or may not reliably maintain polarity, depending on the electrical code and the socket configuration. A fuse in the neutral conductor would be redundant and should it operate (open), the voltages applied to the various circuits will change and could cause overvoltage, overcurrent, and overheating conditions in at least one of the individual loads. 120-0-120 equipment), a fuse in each phase conductor provides protection for both phase-to-neutral and phase-to-ground faults. In these cases, the fuse location is not variable because any polarity reversal (other than phase rotation) results in incorrect voltages applied to the equipment, usually with immediate catastrophic results, and opening of the building fuse or circuit breaker.įor these cases (plug-and-socket-connected three phase equipment and multi-voltage, e.g. 120-0-120) supplies, the plug and socket must maintain polarity in order to have functionality. If we are dealing with plug-and-socket-connected equipment, then we must examine the supply configuration, socket configuration, plug configuration, and wiring codes to determine whether fuse location is variable or not.įor three-phase (e.g. The NEC, CEC, IEE Wiring Regulations and IEC 364 specifically prohibit fusing the neutral in building wiring and permanently-connected equipment. In this case, one fuse, in the phase conductor, provides protection for both phase-to-neutral and phase-to-ground faults. If we are dealing with building wiring or permanently-connected equipment, then fuse location is not variable, and polarity reversal is not possible. The third question that must be addressed is: Is polarity (phase-neutral) reversal possible in the circuit on the supply side of the fuse? That is, is the fuse location (ie: phase or neutral conductor) constant or variable?īuilding Wiring and Permanently-Connected Equipment With double fusing, protection against both faults is provided for both normal polarity and reverse polarity. If polarity reversal is possible, then double-fusing guarantees that the phase conductor will always be provided with a fuse. That is, where the phase and neutral conductors could be interchanged on the supply side of the fuse. The only condition where fusing both phase and neutral conductors yields non-redundant protection against both faults is where polarity reversal is possible. ![]() If double fusing is employed, the equipment is protected against both faults, but the neutral fuse is redundant for phase-to-neutral faults, and inoperative for phase-to-ground faults. We have already determined that a single fuse in the phase conductor provides adequate protection against both kinds of faults, and that a fuse in the neutral conductor does not. The second question that must be addressed is: Under what conditions does double-fusing provide the same or better protection than a single fuse? This is one reason why a single fuse in the neutral is not permitted. Hence, the over-current does not occur, and a fuse cannot provide protection).Ī single fuse in the phase conductor provides protection for both kinds of faults.Ī single fuse in the neutral conductor provides protection for neutral-to-phase faults, but not for phase-to-ground faults. In accordance with Kirchoff’s Laws, the current in the neutral goes down, not up. In a neutral-to-ground fault, the neutral and ground conductors become parallel conductors. (Note that a fuse cannot provide protection for a neutral-to-ground fault because, by definition, the neutral is grounded. There are two kinds of faults: (1) phase-to-neutral (pole-to-pole) and (2) phase-to-ground. The first question that must be addressed is: What fault protection is the fuse providing? Every once in a while, someone asks the question of whether fusing both sides of the power line is safe and permissible. ![]()
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