Café-Bakery Addition: A Load Letter That Fails Recalculation
A 40-year-old two-storey building has a 120/240 V single-phase, 200 A overhead service. The ground floor is a 110 m² café-bakery; the upper floor is a 95 m² dwelling unit. The owner is adding an 11.5 kW deck oven, a 2.0 kW proofing cabinet and a 5.5 kW espresso machine, all on new 240 V circuits. The contractor's load letter adds every nameplate on the service and arrives at 205 A, then argues the 200 A service is adequate 'because the total is essentially the service rating.' The existing inventory lists 3.2 kVA of lighting and 6.0 kVA of general-use receptacles in the café, 4.8 kVA of refrigeration, and in the dwelling an 8 kW range, a 5 kW dryer, a 3 kW water heater and a 5 kW air conditioner. Utility meter data show a 30-day maximum demand of 141 A. The contractor has already bought the replacement 200 A panel and wants the rough-in approved today.
1. Recalculate the service load with the demand-factor method appropriate to this mixed occupancy and state whether 200 A is sufficient. Show the arithmetic.
Read the worked answer
The contractor's error is addition instead of calculation: a nameplate sum is not a calculated load, and the service rating is a limit to compare against, not a target to meet.
Standard method:
- Lighting 3.2 kVA × 1.25 (continuous) = 4.0 kVA
- General-use receptacles 6.0 kVA at 100 % (under 10 kVA) = 6.0 kVA
- Refrigeration 4.8 kVA × 1.25 = 6.0 kVA
- Deck oven 11.5 kVA × 1.25 = 14.4 kVA
- Proofing cabinet 2.0 kVA × 1.25 = 2.5 kVA
- Espresso machine 5.5 kVA × 1.25 = 6.9 kVA
- Water heater 3.0 kVA × 1.25 = 3.75 kVA
- Range, one unit ≤ 12 kW, demand table = 8.0 kVA
- Dryer, 5 kVA minimum = 5.0 kVA
- Air conditioner 5.0 kVA
- 25 % of largest motor (A/C) = 1.25 kVA
Total ≈ 62.8 kVA → 62 800 ÷ 240 V = 262 A.
Two cross-checks. First, continuous load: a 200 A service may carry at most 160 A continuously (80 %); 262 A exceeds both the rating and the continuous allowance. Second, the neutral: the 240 V appliances contribute nothing, and the 120 V lighting, receptacle and refrigeration load plus 70 % of range and dryer is roughly 20 kVA, about 85 A - the neutral does not govern, the phase conductors do.
The next standard rating is 300 A, or a 320 A continuous/400 A meter-main assembly. The panel already purchased is unusable.
2. The contractor proposes to keep the 200 A service and justify it with the utility meter data. Evaluate that proposal and state exactly what documentation you would require.
Read the worked answer
The existing-demand method is legitimate in principle but the numbers do not support him.
Method: documented maximum demand over a representative 30-day period, plus the new load added at 125 % for the continuous portion.
- New continuous load: 14.4 + 2.5 + 6.9 = 23.8 kVA → 99 A at 240 V.
- 141 A + 99 A = 240 A, well above 200 A.
- Even if the new load were added at 100 % (19.0 kVA → 79 A), the result is 220 A - still a fail.
Note also that the measured 141 A is already 88 % of a 200 A service, so there is no headroom to sell.
Documentation to require before the method may even be considered:
- A recording-meter printout or utility demand record, serial number and calibration date shown.
- The interval length and the interval in which the peak occurred.
- Evidence the 30-day window includes simultaneous peak conditions - bakery oven and air conditioning both running. A winter record for a summer-peaking building is worthless.
- A signed statement that no existing load has been removed or will be added.
- A revised calculation sheet, dated and signed by the responsible designer, not a handwritten note.
Only items 1–5 together make the method auditable; anything less and you must fall back to the 262 A calculation.
3. Write the inspection decision and the record entry you would leave for this visit.
Read the worked answer
Decision: not approved for the service rough-in; the wiring methods installed may be inspected separately.
Record entry should contain, in this order:
- Date, time, permit number, weather, persons present and their roles.
- Documents reviewed: contractor's load letter, existing load inventory, utility demand data.
- What was actually examined: the load letter and the existing service, not concealed raceways.
- Finding, stated numerically: calculated demand 262 A against a 200 A service; continuous allowance 160 A exceeded.
- Deficiency and corrective action: submit a demand-factor calculation; upgrade to a minimum 300 A service (or 320/400 A assembly) sized with conductors and neutral to match; submit a revised panel schedule and a revised permit application.
- Explicit note that the contractor's 'essentially at rating' argument was considered and rejected, and why: nameplate summation is not a calculated load.
- What was not verified and what will be verified at re-inspection.
- Re-inspection conditions and who to contact.
Write it so a third inspector, a supervisor or an appeals board can reproduce your arithmetic from the file alone. Never record a verbal assurance as a basis for approval, and never sign a rough-in approval conditional on a future calculation.