Rural Cabin Service Upgrade: Load Calc and Feeder Sizing
A homeowner near Wasilla wants to upgrade a 1960s cabin from a 60 A fuse panel to a 200 A service. The dwelling is 1,450 sq ft heated by a 15 kW electric furnace with a 3 kW blower included in that rating. Appliances: 40 gal water heater (4,500 W), electric range (8 kW nameplate), 1.5 hp well pump (2,400 VA), clothes dryer (5,500 W), and a 30 A receptacle for a future shop. The utility requires a 240/120 V single-phase service. The existing meter base is on a pole 90 ft from the house, and the homeowner wants the new panel inside the utility room. The inspector notes the calculated load must be documented before the permit is approved.
1. Using the standard residential calculation method, determine the calculated demand load in amperes and state whether a 200 A service is justified.
Read the worked answer
General lighting: 1,450 sq ft × 3 VA = 4,350 VA. Small appliance + laundry circuits: 1,500 + 1,500 = 3,000 VA. Total general = 7,350 VA; apply demand: first 3,000 at 100% = 3,000, remainder 4,350 at 35% = 1,522.5 → 4,522.5 VA.
Range: 8 kW nameplate → Table demand for one range 8–12 kW = 8,000 VA (use nameplate if lower than table column). 8,000 VA.
Dryer: 5,500 W → minimum 5,000 VA per code, but nameplate is higher, so 5,500 VA.
Water heater: 4,500 VA at 100% (fixed appliance, largest motor rule applies only to motors).
Well pump: 2,400 VA at 100%; add 25% of largest motor = 600 VA → 3,000 VA.
Furnace: 15,000 VA at 100% (heating load; compare against A/C - none).
Shop receptacle (30 A, 240 V): 7,200 VA, but this is an optional/future load; if included at 100%, total rises. Conservatively include at 100%.
Sum: 4,522.5 + 8,000 + 5,500 + 4,500 + 3,000 + 15,000 + 7,200 = 47,722.5 VA.
At 240 V: 47,722.5 ÷ 240 = 198.8 A. A 200 A service is marginal - it is code-justified only if the future shop load is excluded or diversified. Recommend documenting the calculation and either dropping the 30 A future circuit from the demand or sizing to 320 A/400 A if the shop is built. The inspector's concern is valid.
2. The meter is 90 ft from the house. What conductor and raceway considerations apply to the service-entrance conductors between meter and panel, and what voltage-drop check should be performed?
Read the worked answer
The conductors from the meter to the main disconnect are service-entrance conductors, not a feeder, so they must be sized per Article 230 and protected by the service overcurrent device. If the main disconnect is at the panel inside, the conductors are unprotected service conductors and must be in a raceway or cable approved for service use, with physical protection where subject to damage.
For a 200 A service, minimum is 2/0 Cu or 4/0 Al (75°C terminals). At 90 ft one-way (180 ft round trip):
VD = (2 × L × I × R) ÷ 1000 for kcmil, or use R per 1,000 ft.
For 4/0 Al at 75°C, R ≈ 0.105 Ω/1,000 ft. VD = 2 × 90 × 200 × 0.105 ÷ 1000 = 3.78 V, or 1.6% at 240 V - acceptable (NEC recommends ≤3% on feeders, ≤5% total).
If 2/0 Cu (R ≈ 0.081): VD = 2 × 90 × 200 × 0.081 ÷ 1000 = 2.9 V (1.2%).
Both are fine for voltage drop; the governing issue is conductor ampacity and terminal temperature rating, plus burial depth (24 in for direct burial, 18 in for rigid metal conduit under 2 in, etc.) and the requirement that the meter base be bonded and grounded per Article 250. The inspector should verify the grounding electrode conductor is sized per 250.66 and that the neutral is bonded only at the service disconnect.