Restaurant Tenant Addition: Can the Existing 200 A Service Carry It?
A tenant improvement adds cooking equipment to a 1,400 sq ft restaurant served by an existing 120/208 V, 3-phase, 4-wire, 200 A service. The designer's existing calculated demand load is 118 A. New loads are a 6.0 kW, 208 V, 3-phase booster heater marked "continuous duty," a 10.0 kW, 208 V, 3-phase convection oven that cycles on a thermostat, and 2.4 kVA of new 120 V lighting balanced across the panel. The panel bus is rated 200 A, terminations are rated 75 °C, and 12 spaces are spare. The general contractor wants to skip a service upgrade and asks you to confirm the existing service can carry the addition, size the branch circuits, and explain what happens if the math comes up short.
1. Calculate the added load and determine whether the existing 200 A service is adequate. Show the current for each new load.
Read the worked answer
Convert every load to amps at 208 V, 3-phase (I = VA ÷ (208 × 1.732) = VA ÷ 360.2).
- Booster heater, 6,000 W, continuous: 6,000 ÷ 360.2 = 16.7 A. Because it runs 3 hours or more, apply 125% for the continuous portion: 16.7 × 1.25 = 20.8 A.
- Convection oven, 10,000 W, thermostat-cycled (noncontinuous): 10,000 ÷ 360.2 = 27.8 A (no 125% multiplier).
- Lighting, 2,400 VA, balanced 120 V: 2,400 ÷ 360.2 = 6.7 A per phase (balanced, so it adds as a 3-phase load).
Added demand: 20.8 + 27.8 + 6.7 = 55.3 A New total: 118 + 55.3 = 173.3 A, which is 87% of the 200 A bus.
Judgment: the service is adequate, but only because the existing 118 A figure is a calculated load, not a metered reading. Before you tell the GC to proceed: (1) confirm the panel bus and main are both 200 A (a 200 A main on a 125 A bus is common in older tenant spaces); (2) confirm the neutral and grounding bars can accept the added 120 V lighting neutrals; (3) verify available fault current against the panel's interrupting rating if the utility transformer has changed. If the existing 118 A turns out to be an unmetered estimate, re-run it as a code calculation before signing off.
2. Size the branch circuit for the booster heater and the branch circuit for the oven. Terminals are 75 °C; conductors are copper THHN in EMT in a 95 °F kitchen.
Read the worked answer
Booster heater (continuous):
- Load with 125%: 16.7 × 1.25 = 20.8 A
- Overcurrent device: next standard size at or above 20.8 A = 25 A
- Conductor: must have ampacity ≥ 20.8 A. 10 AWG copper THHN at 75 °C = 35 A, so 10 AWG works even after ambient correction (0.96 factor at 95 °F for 90 °C insulation, and 75 °C column applies at terminations anyway).
- Result: 10 AWG copper, 25 A breaker.
Convection oven (noncontinuous):
- Load: 27.8 A; no 125% multiplier.
- Overcurrent device: 30 A standard size.
- Conductor: 10 AWG copper at 75 °C = 35 A ≥ 27.8 A, so 10 AWG copper, 30 A breaker.
Note for the estimator: these are minimums. If the run exceeds roughly 100 ft, check voltage drop (3% branch circuit recommended) - at 27.8 A and 208 V, 10 AWG has about 1.2 V drop per 100 ft, so a 150 ft run would land near 2.6 V and push you to 8 AWG. Price the larger conductor in the bid rather than absorbing it later.
3. A revised calculation shows the new total demand at 214 A. The GC proposes swapping the 200 A main breaker for a 225 A and calling it good. How do you respond, and what are your realistic options?
Read the worked answer
Reject the breaker swap. The panel bus is rated 200 A. A 225 A main on a 200 A bus violates the panel's listing - the busbar, not the breaker, sets the limit. Upsizing the main also does nothing for the service-entrance conductors, meter socket, or utility service drop, all sized for 200 A.
Realistic options, cheapest first:
- Reduce load. Convert the 10 kW electric oven to gas, or substitute a smaller booster. Removing 27.8 A brings the total to 186 A - back under 200 A with no service work.
- Load management. A listed energy-management/load-shedding system that interlocks the booster and oven can be documented as reducing the calculated demand. This requires a written design, not a verbal promise, and some jurisdictions will not accept it on a restaurant.
- New service. 400 A single-phase or 400 A 3-phase, new meter, new service-entrance conductors, utility coordination - 4 to 8 weeks of lead time and a real cost item.
Process: whichever path is chosen, submit a revised load calculation with the permit revision before any work is energized. Do not let the GC start the rough-in on the assumption that "the inspector won't check." If the calculation changes after contract signing, issue a written change order with the cost and schedule impact - an oral instruction to "just make it work" leaves you holding the risk.