Electrical design of a Pivot system

Categories: Center Pivot

main control panelElectrical design of a center Pivot system is dependent on a number of factors: length of system, number of drive units, options (hi-speed and/or booster pump) and voltage available at the Pivot.

Motors requiere a certain quantity of electricity (amps), that is based on the load of the system, number of motors, amp draw of motors… There is a limit to the amount of electricity components can safely handle: disconnects, contactors, collector rings and the wire size. The limit is 45 amps, although other constraints would probably not allow the average continuous amps to reach that level. Standard electrical components are rated up to 30 amps. Systems having amp draw above 30 will require the 45 amp package, which includes a Pivot panel with higher capacity disconnect and contactors along with a larger capacity collector ring. Other drive unit fuse packages will also be required.

The voltage necessary for proper operation of the equipment is based on the voltage required at the end tower. 440 VAC with 60 Hz power is the minimum allowable (USA), 360 VAC with 50 Hz power (Europe). Just as there is friction loss in a pipeline, there is voltage loss through the span cable on an irrigation system. Electrical losses are based on quantity of electricity required, size of conductors and span cable length.

1300 ft. length systems use the standard 30 amp components along with 10AWg conductors for the 460/380 supply.

As systems increase in length and/or various options are added that require additional power, it becomes necessary to reduce the voltage drop. This is accomplished by increasing the wire sizing, or by adding a device to boost the voltage. Even with the heavier wire and booster transformers, there are still limits to length and load while maintaining the end tower voltage requirement.

The 3 tables below provide information about fuse sizes. They are based on a Pivot voltage of 460 volts. It’s possible that in some instances booster transformer could be deleted if a higher Pivot voltage were available.

No Booster Pump
Electrical Packages (Amp) Up to 30 30 to 45
45 Amp Pivot Package 0 1
Drive Unit Fuse Package 0 1
2HP Booster Pump
Electrical Packages (Amp) Up to 30 30 a 45
45 Amp Pivot Package 0 1
Drive Unit Fuse Package 0 1
5 HP Booster Pump
Electrical Packages (Amp) Up to 30 30 a 45
45 Amp Pivot Package 0 1
Drive Unit Fuse Package 1 1

8 WGA to 10 WGA wire fuse package. Required when average continuous amps exceed 30, the Pivot voltage is greater than 460 and booster transformer is not used.

Booster transformer package. Provides for voltage boost on system with high voltage drop due to length of system and/or accesories (hi-speed, booster pump).

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