Backyard Aquaponics
A place to discuss aquaponics

For pulling wire: Always run no more than 3- 90 degree turns underground and if possible, use 2-45's instead of 90's for easier pulling. You can avoid "pulling" wire as conduit is installed (thread thru as fittings added, without regard for 3-90's maximum rule), and only add pull wire or a string to future (empty) runs. It's nearly impossible to pull additional jacketed cables after the first one is in place; and difficult to add single wires, so best to pull all conductors at same time, even if fill is 50% or less. Schedule 80 PVC is minimum; riser post can be PVC also (1" Sch 80 minimum size), with waterproof(gasketed) box and weatherproof cover for Receptacles. The post can be protected using a riser rod/rebar or pipe.

A Ground rod is only required at original service/main box to connect ground if the branch neutrals and ground wire are extended to load box. Not required at load except for lightning protection of large motorized equipment (bonding). The motor/pump case ground should be connected to the green conductor.
As long as the ground fault is "returned" to the main and breaker, then the breaker will trip, especially if a ground-fault breaker GFI is used. A ground-fault receptacle and/or breaker is only required for wet/outdoor receptacle circuits, not hard-wired loads, by code. GFI's are for 110V typically, and not used for branch 220V, as the neutrals are split downstream and may cause nuisance tripping.

Best to use the full amps of the 10 awg extension (if 4-Wire- two hots and a neutral and ground) by use of a 2-pole 30-amp branch breaker at the 220V panel.
Add a 50-amp box or load panel that allows you 2 or more 110V circuits, as each can be loaded up to 15 amps without tripping the branch breaker.
Most 110V loads will run less than 7.5 amps at the same time, so (4) single-pole 15 or 20 amp breakers can be used to fill small box/panel, using the "diversity" allowance. This is a standard "quad box" drop for 30A/2P (amp/pole) circuit, and 4 single 15A/120V receptacles can be used, or 2- 220V, 20 A twistlocks.

It may be a problem if you are switching a full 15 amps on the pump; the pump starting current could cause a voltage drop on the start relay AND spinkler valve timer, causing a malfunction.
It should work if the pump starts easily or has low amps draw for the "extension cord".
A larger circuit awg for the 110 volt could solve if the pump is borderline, or a start/run capacitor can be added for the pump extension only. Water well pumps have the capacitor even for 220V in the start relay when the pumps are down-well.

Voltage Drop/Power Factor Course 101:
Amps draw, no matter what the voltage, will always create voltage-drop on circuits, so 220 volt (2-pole breaker feed) will only double the power capacity for the same size conductors. The efficiency of the motor is not affected, and is still limited by the service factor (wiring/rotor design) and the Power Factor for using supplied voltage and amps at the end of a conductor run of fixed length and size.
NEC (National code) recommends that 20-amp circuits over 100 feet long use 10 AWG instead of 12 AWG if the load pulls over 15 amps. 220 Volt single phase is recommended for larger than 1/4HP, and Three-phase is recommended for larger than 1HP.
On very long runs (300+ ft.), or higher-amp/small conductor loads, voltage drop and power factor losses must be calculated.

Any induction motor, single or three phase, uses reactive power, or VAR (volt-amps reactive) as part of the field creation and induction of the rotor. Induction motors have a power factor rating of less than 100%, usually 85-90%.
The lower the power factor on the motor, the less efficient, and amps/voltage-drop goes up, unless you supply "storage" for the VARs on line, or at the motor.
A capacitor will help start, and supply running VARs and reduce the amp draw and voltage drop for long lines and large motors, with less need for larger conductor size.
Less amps draw at start will also reduce the damage to the contacts on the starter.

The Franklin starters (like at Lowes, Sears, etc) have these for only a 6 to 8 amp running load pump. My brother uses a 1 HP starter (with a larger capacitor) for his 3/4 HP, 220V Well pump as it adds a little more backbone and reliability to the circuit, at the pump-head end where it does the most good.

Happy pumping!