Service Upgrade for a Growing Restaurant
A restaurant owner wants to add a 12 kW commercial range and two 5 kW fryers to an existing 120/240 V single-phase service. The existing service is 200 A with a calculated load of 150 A. The service panel has a 200 A main breaker and a 40-space panelboard with 10 spare spaces. The owner also plans to add a 3 kW sign circuit and a 7.5 kW water heater. The utility transformer is 50 kVA and the service drop is 2/0 AWG aluminum. The local AHJ requires a load calculation per NEC Article 220. The restaurant is in a strip mall with other tenants.
1. Calculate the new service load and determine if the existing 200 A service is adequate.
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First, compute the existing load: 150 A at 240 V = 36 kVA. Add new loads: range 12 kW, fryers 2×5=10 kW, sign 3 kW, water heater 7.5 kW. Total new connected = 32.5 kW. Apply NEC 220.56 for commercial kitchen equipment: three units (range + two fryers) total 22 kW, demand factor 90% (Table 220.56) = 19.8 kW. Sign circuit: 3 kW at 100% (220.14(F)). Water heater: 7.5 kW at 100% (220.51). New load = 36 + 19.8 + 3 + 7.5 = 66.3 kVA. Current = 66,300 / 240 = 276 A. The existing 200 A service is inadequate; a minimum 300 A service is required (next standard size per 240.6). Also note the 50 kVA utility transformer (208 A) is undersized for the new load.
2. What minimum size service conductors and main breaker would you specify? Consider NEC 310.15(B)(16) and 240.6.
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From the calculated load of 276 A, the service conductors must have an ampacity of at least 276 A. Using Table 310.15(B)(16) for 75°C copper conductors: 300 kcmil = 285 A, so 300 kcmil copper is sufficient. For aluminum: 350 kcmil = 270 A (not enough), 400 kcmil = 305 A, so 400 kcmil aluminum. The main breaker must be at least 276 A; standard sizes per 240.6: 300 A is the next standard. However, the conductor ampacity must be at least the load, but the breaker can be the next standard size if the load does not exceed the conductor ampacity? Actually, 240.4(B) allows next standard breaker if conductor ampacity is less than breaker rating but load is less than conductor ampacity. Here load 276 A, conductor 285 A, so 300 A breaker is acceptable. So specify 300 A service with 300 kcmil Cu or 400 kcmil Al, and a 300 A main breaker.