You can share ground, but I believe you'll get into code issues if you share the neutral, so you'll need 5 wires (Hot 30 Neutral 30 Hot 20 Neutral 20 Ground 20&30) even though the neutrals probably could be shared from a purely electrical point of view.
Ah, wait - you're saying you'd put a 30A 220V sub-panel on the post, so you'd just need the 4 conductors (L1, L2, N, G) to feed that, and then you'd run the receptacles from that sub-panel. Should work and pass code, don't know that it will be cheaper given the need for an exterior-rated sub-panel and a breaker to feed it. Wire is expensive, but maybe not THAT expensive.
Personally, I'd run 1" schedule 80 conduit and pull individual wet-rated wires rather than run a cable. But that's an opinion
Sounds like you're wired up properly, but may have a bad neutral in your service drop.
Call the utility, and ask them to check the service.
Extra Reading
Single Split-Phase Service Overview
To understand what's going on, you have to understand a bit about how a 120/240V single split-phase system works. The system looks something like this.
Where the transformer primary will have a high voltage applied to it (say 7.2 kV), and the secondary provides a lower voltage (240 V). The secondary winding is center tapped, providing the "neutral" leg of the service. When measuring voltage from either of the "hot" legs to the "neutral" leg, you'll measure half the voltage (~120 V).
Normal Operation Examples
NOTES:
- For simplicity sake, the following examples will represent a single light bulb connected to each leg of the service, and will not consider the resistance of the wiring.
- H1 = The ungrounded (hot) conductor at the top of the diagram below.
- H2 = The ungrounded (hot) conductor at the bottom of the diagram below.
- N = The grounded (neutral) conductor (center tap).
Example 1:
For this example R1 is a single 60 watt light bulb, and R2 is a single 100 watt light bulb.
Resistance
The resistance of R1 will be 240 ohms, while the resistance of R2 will be 144 ohms.
Current
The current on H1 will be 0.5 amperes, and the current on H2 will be 0.8333 amperes. Because the grounded (neutral) carries the unbalanced current, the current on N will be 0.3333 amperes.
Voltage
Measuring the voltage across R1 (H1 -> N), will yield 120 V. Voltage across R2 (H2 -> N) will also be 120 V, and voltage across both loads (H1 -> H2) will be 240 V.
Now let's look at the same example, but with a dropped neutral.
Example 2:
For this example R1 is a single 60 watt light bulb, and R2 is a single 100 watt light bulb. The only difference, is that the grounded (neutral) of the service is broken.
Resistance
The resistance of the bulbs has not changed, so R1 is still 240 ohms and R2 is still 144 ohms. Now that the neutral is gone, it's no longer a split-phase system. Instead, it's a 240 volt single phase system. Because of this the loads are now connected in series, so to get the total resistance, the individual resistances have to be summed.
Rt = R1 + R2 = 384 ohms
So the total resistance in the circuit, is 384 ohms.
Current
Since it's now a single circuit, both H1 and H2 will see the same current.
It = Et / Rt = 240 volts / 384 ohms = 0.625 amperes
Voltage
Since there's no longer a neutral, this is a simple 240 volt circuit. Therefore, measuring from H1 to H2 will yield 240 volts. However, if measure across each load individually (H1 -> N, H2 -> N), you'll see the voltage dropped across that load.
V1 = It * R1 = 0.625 amperes * 240 ohms = 150 volts
V2 = It * R2 = 0.625 amperes * 144 ohms = 90 volts
What happens if we swap out the 60 watt bulb, for a 120 watt bulb?
Example 3:
For this example R1 is a single 120 watt light bulb, and R2 is a single 100 watt light bulb.
Resistance
R1 = 120 ohms
R2 = 144 ohms
Rt = R1 + R2 = 120 + 144 = 264 ohms
Current
It = Et / Rt = 240 volts / 264 ohms = 0.90909090 amperes
Voltage
V1 = It * R1 = 0.9090 amperes * 120 ohms = 109.090909 volts
V2 = It * R2 = 0.9090 amperes * 144 ohms = 130.909090 volts
As you can see from the examples. If the service neutral is bad (dropped), you'll end up getting some strange readings when measuring voltage. This is because you're no longer reading the voltage drop across an entire circuit, you're only reading the voltage dropped across the loads in half the circuit.
Best Answer
the "I own a copper mine" version
If you own a copper mine, wire cost is no object. Sell your copper at market and buy aluminum. Assuming we're running just the lump at 10A, and aim to confine voltage drop to the stock-advice 3%, we will need 3/3/3/6 aluminum cable.
If you also want to run an honest 20A of loads in total, we will need 2/0-2/0-2/0-1 cable ($3000).
If you want a full 30A still at 3% voltage drop, you'll need 4/0-4/0-4/0-2/0 cable ($5000) .
We need neutral because you have 120V stuff to run that apparently you cannot source in 240V for some reason.
We need ground because using a ground rod instead does not provide fault current protection. You also need a ground rod.
You will need a disconnect at rhis location . This is as easy as using a subpanel which has a main breaker. Size does not matter as long as it is>= the supply breaker. Remember it must also have separate ground and neutral bars.
The stock advice, no-brainer version
See "I own a copper mine" .
The "I do not own a copper mine" version
in which cost is considered worthy of attention. Ok, 2.4 KW for the pump, somewhat less for heat and light, say we can get this done in 5 KW. 5 KVA transformers are often seen on Craigslist for $100ish, we need two. Probably 480V transformers, if possible get 600V, popular in Canada.
The transformers will be used back to back, to step up transmission voltage, reducing voltage drop dramatically. At the far end, it will give 120/240 split-phase.
Amps will be 10.42@480V or 8.3@600V. We are going for 6% voltage drop at max power since draw will usually be half that (and thus 1/4 the drop).
Either way, #8 Al will suffice or #10 Cu ($500). We only need 2 wires.
Why no neutral? We will be manufacturing neutral locally. Why no ground? Irrelevant since the transformers double isolate the service.
Since our final output transformer has no earth ground reference, we must provide one with a local ground rod. All this would make this a main service in need of a main breaker, and as a main service, neutral would be tied to ground here. The technical term is "separately derived service" .