Planning the Farmstead Distribution System

Planning the Farmstead Distribution System - Planning the...

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1 Planning the Farmstead Distribution System Notes taken from chapter 5 of Gustafson, Fundamentals in Electricity for Agriculture, 1988 Planning the Farmstead Distribution System ± Electrical equipment and electronics on the farmstead are producing an ever-increasing demand for electricity. A well-designed farm wiring system must distribute electricity economically and efficiently both today and in the future. Planning the Farmstead Distribution System con’t ± A well-planned system must be safe, adequate to meet power demands, efficient, and expandable. Compliance with the National Electric Code (NEC) or prevailing code in the region is required to ensure safety. ± The wiring system must have properly selected electrical components, with a main service and building service entrances of sufficient capacities to supply the required power.
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2 Planning the Farmstead Distribution System con’t ± The distribution system must have enough branch circuits and outlets of proper size and type, which are correctly located to meet the farmstead’s electrical needs. ± Three types of costs are considered important: initial cost, maintenance costs, and the cost of energy lost in delivery. Minimizing initial cost could sacrifice operating efficiency and thus increase overall costs. Demand Load for Farm Buildings ± The first step is to determine the demand load for each building or service area. The term service area refers to loads, such as buildings, grain drying and handling systems or pumping stations. Demand Load for Farm Buildings con’t ± A demand load must be determined for each building individually. ± This system presents a methodology for combining known and anticipated loads within a building to determine a demand load by which to size the service for the building. The method is taken from NEC section 220-40.
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3 Demand Load for Farm Buildings con’t ± Since it is very unlikely that all loads in a service area will operate at one time, the NEC suggests a method for determining the maximum demand load. This demand load is then used to select the correct ampacity of service for the building. Demand Load for Farm Buildings con’t ± List known and anticipated loads: 1. Large or permanently connected machines or appliances. The full-load ratings of all equipment rated at or above 1500 W (1 hp) are included in this category. The full-load current of the larger motor should be multiplied by 125% to allow for a 25% overload of the motor. Demand Load for Farm Buildings con’t 2. A load of 1.5 A at 120 V (0.75 A at 240 V) should be allotted for each convenience outlet. This accounts for portable tools and appliances not listed in #1. 3. A load of 1.5 A at 120 V (0.75 A at 240 V) should also be allotted for each lighting outlet.
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4 Demand Load for Farm Buildings con’t ± Complete list by calculating the amperage at 240 V required to service each load. Amperage at 120 V is converted to amperage at 240 V by dividing amperage at 120 V by 2. ± The amperages converted to 240V will
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Planning the Farmstead Distribution System - Planning the...

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