6.6 Farm Load Calculations (2026 NEC 120.102 & 120.103)

Why farm calculations matter in Minnesota

Minnesota has thousands of farms with barns, machine sheds, grain bins, and dryers fed from one utility service. Farm load calculations are in Part V of Article 120 (formerly 220.100 to 220.103). They apply to farm buildings and loads other than the dwelling, and they recognize that farm loads in different buildings rarely peak at the same time.

Step 1: each farm building or load (120.102)

120.102(A) Dwelling unit: the farm dwelling is calculated by the standard method or the optional method in 120.82. If the dwelling has electric heat and the farm has electric grain-drying systems, the optional method may not be used for the dwelling when the dwelling and farm loads share a common service.

120.102(B) Other than dwelling unit: where a feeder or service supplies a farm building or other load with two or more separate branch circuits, the load for feeders, service conductors, and service equipment is calculated with demand factors not less than those in Table 120.102:

The first line uses the largest of the three values: the simultaneous load, 125% of the largest motor, or 60 A.

Step 2: total farm load on a common service (120.103)

Where the farm buildings and loads are supplied by a common service, calculate each building or load under Table 120.102, then combine them:

Add the farm dwelling load, calculated under Step 1, to this total.

Typical farm loads

Farm buildings combine motors, heating, and lighting that run on very different schedules, which is why the demand factors are so generous:

• Grain drying: dryer fans and burners, augers, and bin aeration fans run hard during harvest and little the rest of the year. The dryer site is often the largest load on the farm.
• Dairy: vacuum pumps, milk coolers, water heaters, and ventilation fans run every day, often for long periods.
• Hog and poultry confinement: ventilation fans run continuously, with heaters and lighting on controls.
• Shops and machine sheds: welders, air compressors, and heaters run intermittently.
• Heated stock waterers and heat tape: small but long-running winter loads in Minnesota.

Table 120.102 is stated in amperes at 240 V maximum, so convert other loads to amperes before applying it. The demand factors only reduce the calculated load; feeder and service conductors must still be sized under 215.2 and 230.42, with continuous loads at 125%.

Worked example: a dairy barn

A barn has a total connected load of 150 A at 240 V. The largest motor is a 10 hp, 230 V single-phase vacuum pump with a Table 430.248 full-load current of 50 A. Loads expected to run together total 70 A.

1. 125% of the largest motor: $50 \times 1.25 = 62.5$ A. The first line uses the largest of 70 A, 62.5 A, and 60 A, so 70 A at 100% = 70 A.
2. Next 60 A at 50%: $60 \times 0.50 = 30$ A.
3. Remainder: $150 - 70 - 60 = 20$ A at 25% = $5$ A.
4. Barn demand: $70 + 30 + 5 = 105$ A.

Worked example: total farm service

The same farm has these building loads, each already calculated under Table 120.102: barn 105 A, grain dryer and bins 90 A, machine shed 60 A, shop 40 A. The house calculates to 120 A by the standard method.

A 400 A service, or a 400 A distribution point, is needed.

How farm calculations connect to other rules

• Agricultural buildings (Article 547): a farm's distribution point, often a pole-mounted site-isolating device, feeds the buildings as separate structures. The 2026 NEC adds detailed construction rules for equipotential planes in livestock confinement areas.
• Outside feeders (Article 225): each building fed from the distribution point needs its own disconnecting means, located at or within sight of the building under 225.31 and 110.29.
• Grounding of separate buildings (250.32): each building needs a grounding electrode system and an equipment grounding conductor run with the feeder; the neutral and equipment grounding conductor are not bonded at the building.