Yes, you would treat that as a single-phase 208V circuit for voltage drop calculations. Here's why and what you need

Why Single-Phase Calculation:
Two-Pole Breaker, 208V

A two-pole breaker indicates you're pulling from two legs of a 208V three-phase wye system. However, you are only using the two legs.

Single Voltage

You're only using one voltage (208V) between the two hot conductors. In effect, you're measuring across two phases of the three-phase system.

Information Needed for Voltage Drop Calculation

To accurately calculate voltage drop, you'll need the following information:1.

Load (Amps)

This is the most critical piece of information. You need to know the actual or expected maximum amperage draw of the trailer panel. If you only know the total wattage of the devices it will power, use the following formula: Amps (I) = Watts (P) / Voltage (V) I = P/2082.

Conductor Type and Size

What type of wire are you using (e.g., copper THHN, aluminum XHHW)? And what is the AWG size (e.g., 12 AWG, 10 AWG, 8 AWG)?3.

Conductor Length

The total one-way length of the wire from the breaker to the trailer panel. This is the key factor in determining voltage drop.4.

Power Factor (PF)

If the load is primarily resistive (e.g., heating elements, incandescent lights), a power factor of 1.0 is a reasonable assumption. If there are significant inductive loads (motors, transformers), the power factor will be less than 1.0, and it will increase voltage drop. A typical power factor for mixed loads might be 0.
8. If you don't know the power factor, it's safer to assume a lower value (e.g., 0.8) to get a more conservative (higher) voltage drop estimate.
5.

Acceptable Voltage Drop

What percentage of voltage drop are you willing to tolerate? NEC recommends voltage drop should not exceed 3% for branch circuits or 5% for feeders. It is wise to design for less than 3% on a feeder.

Formula for Single-Phase Voltage Drop

There are variations of the formula, but a common and useful one is:

VD = (2  K  I  D) / CM

Where:

VD = Voltage Drop (in volts) K = Direct-current constant representing the resistance of the conductor material. (Typically 12.9 for copper, 21.2 for aluminum, at 75 degrees C) I = Current (Amps) D = One-way distance (feet) CM = Circular Mils of the conductor (refer to a wire ampacity chart).

Steps


Gather the Information

Collect all the data outlined above (amps, wire type/size, length, power factor).2.

Determine Circular Mils

Look up the circular mils (CM) for the conductor size you are using. Many online wire size charts include this.3.

Apply the Formula

Plug the values into the formula and calculate VD (voltage drop in volts).4.

Calculate Percentage Voltage Drop

%VD = (VD / Source Voltage) 100 %VD = (VD / 208) 1005.

Compare to Acceptable Limit

Compare the calculated %VD to the acceptable voltage drop limit (e.g., 3% or 5%). If it exceeds the limit, you need to: Increase the wire size. Reduce the load (amps). Shorten the conductor length.

Tools and Calculators

There are many online voltage drop calculators available. Search for "voltage drop calculator single phase" and you will find several to choose from. These can simplify the calculation process. Just make sure the calculator allows you to input the correct values for K, Power Factor, and wire type.

Important Considerations



NEC (National Electrical Code)

Always comply with the NEC and local electrical codes. Voltage drop calculations are important for safety and proper equipment operation.

Safety

Working with electricity can be dangerous. If you're not qualified, consult with a licensed electrician.

Future Expansion

Consider potential future load increases when sizing conductors. It's often wise to oversize slightly to accommodate future needs.

Example

Let's say you have: Load: 30 amps Wire: 10 AWG Copper THHN Distance: 100 feet Power Factor: 0.9 K = 12.9 (for copper) Circular Mils (CM) for 10 AWG: 10,380VD = (2 12.9 30 100 0.9) / 10380VD = 67530 / 10380VD = 6.50 volts%VD = (6.50 / 208) * 100%VD = 3.13%In this example, the voltage drop is 3.13%, which is slightly above the 3% limit often recommended for feeders. You might consider upsizing to 8 AWG to reduce the voltage drop.

In summary, treat it as a single-phase 208V circuit. Collect the necessary data (amps, wire type/size, length), and use the appropriate voltage drop formula or an online calculator to determine the voltage drop percentage. Make sure it's within acceptable limits. Flag for review