My apologies‚Ä¶ You are correct, Ell, that the '180 volt-amp per receptacle outlet' rule does not apply to Dwelling Occupancies.
However, you are incorrect that, in other that a dwelling unit, a duplex receptacle must be calculated as 3 amps (360 VA). According to the NEC paragraph 220.14(I), ‚Äú‚Ä¶receptacle outlets shall be calculated at not less than 180 volt-amperes for each single OR FOR EACH MULTIPLE RECEPTACLE ON ONE YOKE‚Ä¶‚Äù . In the NEC Handbook, it goes on to specifically state that single, duplex, and triplex receptacles are all to be calculated at 180 volt-amps PER DEVICE.
Also, the requirement for only using 80% of the rating for branch circuit conductors and overcurrent devices only applies to ‚Äúcontinuous‚Äù loads (see NEC 210.19(A)(1) and 210.20(A)). Per NEC Article 100, ‚ÄúContinuous Load‚Äù is defined as ‚ÄúA load where the maximum current is expected to continue for 3 or more hours‚Äù. Lighting loads are generally considered continuous, while receptacle loads are generally not. For example, the load of a computer or printer will vary up and down depending on activity and usage. They will not maintain a peak load for more than 3 hours.
Next, I never suggested that anyone share a neutral on a ground fault protected circuit. None of the circuits in this home office should require ground fault protection. And a shared neutral is only a problem on a circuit protected by a GFCI breaker. Individual GFI receptacles would not be affected, because they only sense ground faults downstream (i.e. in the cord-and-plug connected load), not upstream.
Finally, while it‚Äôs true that you cannot share a neutral on a circuit protected by a GFCI breaker, your reasoning is completely incorrect, and it will NOT create an unsafe condition. A ground fault device works by measuring and comparing the currents in the hot and neutral wires. Since all current that goes out should come back, a difference means that the current has found a different path to ground (i.e. a ground fault). When a ground fault device senses this difference, which is 5 milliamps for the GFI‚Äôs required for personnel protection, it trips and opens the hot conductor, deenergizing the circuit. If a GFCI breaker is installed for a circuit that shares the neutral, the neutral current will never match the current on either of the hot conductors (it will be less), and thus the GFI will always trip and won‚Äôt reset. The protected circuit will be deenergized, but the other circuit sharing the neutral will continue to operate as before. While this is potentially an unsafe condition, it is no more unsafe than if an unprotected circuit that has a ground fault isn't sharing a neutral.
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