Okay, let's break this down step-by-step to help you calculate the appropriate feeder size and plan your circuit layout, keeping voltage drop in mind.1. Gathering Information (Critical Missing Pieces)



Fixture Wattage & Quantity

You absolutely need the wattage (or VA) of each of the S1 and S2 fixtures. How many S1 fixtures and how many S2 fixtures? Without this, we cannot proceed.

Breaker Size (at the Panel)

The 1P-20A breaker you mentioned is essential information. Is that the size of the breaker feeding everything?

Wire Type and Installation Method

You need to know the type of wire (e.g., THHN, XHHW) and the installation method (e.g., in conduit, direct burial). This affects the wire's ampacity.

Voltage at the Panel

Confirm the voltage is a stable 120V at the panel.

2. Understanding Voltage Drop and the Goal



Voltage Drop Limit

You want to keep voltage drop under 2.5%. This means the voltage at the last fixture should be at least 120V - (120V 0.025) = 117V.

Why it Matters

Excessive voltage drop causes lights to be dim, motors to run inefficiently, and can damage equipment.

3. Estimating Feeder Size (Once You Have the Fixture Information)



Calculate Total Wattage

`Total Wattage = (Wattage of S1 Number of S1 fixtures) + (Wattage of S2 Number of S2 fixtures)`

Calculate Total Current (Amps)

`Total Current (Amps) = Total Wattage / Voltage (120V)`

4. Voltage Drop Calculation



Use a Voltage Drop Calculator

The easiest way to determine if voltage drop is acceptable is to use an online voltage drop calculator. There are many free ones available. You'll need the following information:

Voltage

120V

Current (Amps)

Calculated in step 3.

Wire Gauge (AWG)

Start with a guess (e.g., #6, #4, #2) and iterate.

Wire Type

(e.g., Copper THHN, Aluminum XHHW) This affects the voltage drop.

Conductor Material

Copper or Aluminum

Circuit Length

100ft (panel to j-box) + 250ft (j-box to last fixture) = 350 ft.

Repeat Calculation with different wire sizes until you find a wire size that keeps the voltage drop below 2.5%.5. Considerations for Multiple Circuits



If the 1P-20A Breaker feeds everything

You must calculate the total load (all fixtures) to ensure it doesn't exceed 80% of the breaker rating (16 Amps). If the total load exceeds 16 Amps, you

must split the fixtures into multiple circuits. Splitting into Multiple Circuits

If you split the fixtures into multiple circuits, you'll perform the voltage drop calculation for each circuit separately. Ensure each circuit's load stays within 80% of the breaker rating.

6. Underground "Homeruns" and Branching Off



Underground "Homeruns"

Yes, after you hit the underground j-boxes, you can branch off with smaller wire to the individual light poles, provided that:

The smaller wire is protected by an overcurrent device (breaker or fuse) that is sized appropriately for the ampacity of the smaller wire. This is critical. The voltage drop on the branch circuit to each pole is also considered. While the "main" feeder may have acceptable voltage drop, the added length of the branch circuit could push it over the 2.5% limit. You may need to upsize the branch circuit wire to compensate. All wiring methods and materials are suitable for wet/damp/underground locations.7. Example Scenario (Illustrative Only - You MUST use your actual fixture data)

Let's assume you have: 5 S1 fixtures, each 100W 3 S2 fixtures, each 150WThen: Total Wattage = (5 100W) + (3 150W) = 500W + 450W = 950W Total Current = 950W / 120V = 7.92 Amps

8. Important Considerations



NEC (National Electrical Code)

All electrical work must comply with the NEC and any local amendments. Consult the NEC for specific requirements regarding wire types, ampacities, grounding, and bonding.

Safety

Electrical work is dangerous. If you are not a qualified electrician, hire one.

Future Expansion

Consider future load additions when sizing the feeder. It's often better to upsize now than have to replace it later.

Continuous Load

Lighting is generally considered a continuous load. You must size the feeder to carry 125% of the continuous load (NEC 210.19). In our example, you would need to size the feeder for at least 7.92A * 1.25 = 9.9A

In Summary


GET THE FIXTURE WATTAGE INFORMATION. This is the most important step.2. Calculate total wattage and current.
3. Use a voltage drop calculator to determine the required wire size for the 350ft run, aiming for under 2.5% voltage drop.
4. Verify the total load does not exceed 80% of the breaker rating. If it does, split the fixtures into multiple circuits.5. When branching off to individual poles, ensure proper overcurrent protection and consider voltage drop on the branch circuit.
6. Consult the NEC and a qualified electrician to ensure compliance and safety. Flag for review