wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
Here's what I came up with to eliminate any ambiguity as to the question "for the service to a duplex, can I calculate the load just by adding together the optional load calcs for each dwelling unit?"
Do you think the single phrase added is sufficiently clear? I could try something even more direct, like adding a whole sentence stating "A feeder or service supplying multiple such dwelling units shall be permitted to have its load calculated as the sum of the individual loads of those dwelling units."
Or I could further change the first sentence to say "This section applies to any number of dwelling units, each havingtheits total connected load served by a single 120/240-volt or 208Y/120-volt set of 3-wire service or feeder conductors with an ampacity of 100 or greater"
Cheers, Wayne
120.82(A) Feeder and Service Load.
This section applies to a dwelling unit having the total connected load served by a single 120/240-volt or 208Y/120-volt set of 3-wire service or feeder conductors with an ampacity of 100 or greater. It shall be permissible to calculate the feeder and service loads in accordance with this section instead of the method specified in Article 120, Part III. The calculated load shall be the result of adding the loads from 120.82(B), 120.82(C), and 120.82(D) for each dwelling unit individually. Feeder and service-entrance conductors whose calculated load is determined by this optional calculation shall be permitted to have the neutral load determined by 120.61.
Statement of Problem and Substantiation for Public Comment
Consider a duplex with a single service that supplies two sets of service entrance conductors to two service disconnects, one for each dwelling unit. The service entrance conductors supplying just one dwelling unit can have their load computed using 120.82.
There is, however, some uncertainty as to whether the service conductors supplying both dwelling units may have their load calculated as the sum of those two 120.82 calculations. The current wording of 120.82 leads some AHJs to the interpretation that 120.82 only applies to conductors carrying the load of exactly one dwelling unit, and that the results of that computation can not be used for determining the load on any upstream conductors that supply more than one dwelling unit. This point of view is supported by the observation that 120.84 is available for conductors supplying 3 or more dwelling units, and that 120.85 is available for conductors supplying exactly 2 dwelling units.
However, it makes no sense to limit the calculation results from 120.82 to conductors that supply exactly one dwelling unit. Where a set of conductors supplies multiple other sets of conductors, it is is physically impossible for the load on those conductors to exceed the sum of the loads on the multiple other conductors supplied. Summing those individual loads is always a conservative overestimate of the load on the common supply conductors.
Therefore this change clarifies that conductors that supply multiple dwelling units may have their load determined by calculating the 120.82 load of each dwelling unit separately, and then adding those results.
Do you think the single phrase added is sufficiently clear? I could try something even more direct, like adding a whole sentence stating "A feeder or service supplying multiple such dwelling units shall be permitted to have its load calculated as the sum of the individual loads of those dwelling units."
Or I could further change the first sentence to say "This section applies to any number of dwelling units, each having
Cheers, Wayne
120.82(A) Feeder and Service Load.
This section applies to a dwelling unit having the total connected load served by a single 120/240-volt or 208Y/120-volt set of 3-wire service or feeder conductors with an ampacity of 100 or greater. It shall be permissible to calculate the feeder and service loads in accordance with this section instead of the method specified in Article 120, Part III. The calculated load shall be the result of adding the loads from 120.82(B), 120.82(C), and 120.82(D) for each dwelling unit individually. Feeder and service-entrance conductors whose calculated load is determined by this optional calculation shall be permitted to have the neutral load determined by 120.61.
Statement of Problem and Substantiation for Public Comment
Consider a duplex with a single service that supplies two sets of service entrance conductors to two service disconnects, one for each dwelling unit. The service entrance conductors supplying just one dwelling unit can have their load computed using 120.82.
There is, however, some uncertainty as to whether the service conductors supplying both dwelling units may have their load calculated as the sum of those two 120.82 calculations. The current wording of 120.82 leads some AHJs to the interpretation that 120.82 only applies to conductors carrying the load of exactly one dwelling unit, and that the results of that computation can not be used for determining the load on any upstream conductors that supply more than one dwelling unit. This point of view is supported by the observation that 120.84 is available for conductors supplying 3 or more dwelling units, and that 120.85 is available for conductors supplying exactly 2 dwelling units.
However, it makes no sense to limit the calculation results from 120.82 to conductors that supply exactly one dwelling unit. Where a set of conductors supplies multiple other sets of conductors, it is is physically impossible for the load on those conductors to exceed the sum of the loads on the multiple other conductors supplied. Summing those individual loads is always a conservative overestimate of the load on the common supply conductors.
Therefore this change clarifies that conductors that supply multiple dwelling units may have their load determined by calculating the 120.82 load of each dwelling unit separately, and then adding those results.
