Service Calculation Dispute for a Small Restaurant
A tenant build-out for a small restaurant submits a service calculation for a new 200 A, 120/208 V, 3-phase service. The calculation lists: 12 kW of general lighting and receptacles, a 15 kW electric range, a 6 kW water heater, a 10 kW HVAC unit, and 8 kW of miscellaneous kitchen equipment. The designer applied a 100% demand factor to all loads and concluded the service is adequate at 200 A. The plan reviewer notes the building has an existing 200 A service and the tenant is adding the restaurant in a space previously used as retail. The reviewer must evaluate whether the calculation method and the service rating are correct.
1. Identify the errors in the designer's calculation method and explain how the demand factors should be applied.
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The designer applied 100% to everything, which overstates some loads and understates others depending on the category. The reviewer should require a method-consistent calculation:
- General lighting/receptacles: apply the applicable demand factors for the occupancy, not 100% across the board.
- Range: the range demand factors from the applicable table apply to a single range based on its rating; a 15 kW range is not taken at 100% if the table provides a demand factor.
- Water heater and HVAC: these are typically taken at 100% as fixed appliances, but the larger of heating vs. cooling applies where they are not simultaneous; the designer must state the assumption.
- Miscellaneous kitchen equipment: apply the demand factors permitted for the category, if any, and document them.
- Continuous vs. noncontinuous: apply the 125% factor to continuous loads.
The reviewer should not accept a calculation that applies a uniform 100% factor without identifying each load category and the demand factor used.
2. The designer concludes 200 A is adequate. How should the reviewer verify the service rating, and what should happen if the existing service cannot support the load?
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The reviewer should convert the calculated load to amperes at 208 V, 3-phase and compare to the 200 A service rating, accounting for the 125% continuous-load factor and the service equipment rating. The reviewer must also verify the existing service equipment (busbar, main breaker, meter) is rated for the calculated load, not just the nominal 200 A.
If the calculated load exceeds the service rating, the reviewer should not approve the plans as submitted. Options include requiring a service upgrade, reducing connected load, or providing a documented load-management approach acceptable to the jurisdiction. The reviewer documents the calculation basis and the deficiency, and withholds approval until a corrected calculation and any service upgrade are shown.