Okay, let's break this down and clarify some potential misunderstandings and ensure we're on the right track for a safe and compliant installation. It seems there might be a few points of confusion in your description.Here's a detailed analysis

1. Terminology and Understanding
Service vs. Feeder

A "service" is the connection from the utility company. It sounds like you're describing a feeder running from a panel to the transformer. This is an important distinction.

Transformer Load Side

You stated the load side voltage is "45kv". This is extremely high. You should be stepping down to 208v to power the scoreboard equipment. If your load is using 45kv equipment, your calculations and wire gauge are incorrect. Please verify what voltage the load equipment operates at.

2. Calculations and Wire Size Verification (480V Side) Assumptions

450 ft feeder run. 120 amp load at 480V, 3-phase. Aluminum conductors. Target voltage drop: ~3% (reasonable).

Voltage Drop Calculation

You mentioned using 2/0 aluminum. Let's verify that using a common voltage drop formula:Voltage Drop (VD) = (√3 I R D) / 1000Where: I = Current (120 amps) R = Resistance per 1000 ft of conductor (Aluminum 2/0 @ 75°C = 0.268 ohms/1000ft from NEC Chapter 9, Table 8) D = One-way distance (450 ft)VD = (1.732 120 0.268 450) / 1000VD = 25.03 voltsPercentage Voltage Drop = (VD / Source Voltage) 100Percentage Voltage Drop = (25.03 / 480) 100Percentage Voltage Drop = 5.21%

Analysis

Your calculation is off. 2/0 aluminum will result in approximately a 5.21% voltage drop, not 2.91%. This is above your target of 3%. You will need to consider a larger wire size. To achieve a lower voltage drop on the 480 volt side, you will need to use larger conductors such as 3/0 or 4/0 aluminum.

Ampacity Check

2/0 Aluminum ampacity (75°C rating, typical) = 135 amps (NEC Table 310.16/310.15(B)(16)). This is barely sufficient for a 120 amp load. Larger conductors will give you greater flexibility. 3/0 Aluminum ampacity (75°C rating, typical) = 155 amps (NEC Table 310.16/310.15(B)(16)). 4/0 Aluminum ampacity (75°C rating, typical) = 180 amps (NEC Table 310.16/310.15(B)(16)).

3. Transformer Considerations Transformer Size (KVA)

Your 120 amp load at 480V, 3-phase, requires a transformer of approximately: kVA = (Volts Amps √3) / 1000 kVA = (480 120 1.732) / 1000 kVA ≈ 99.8 kVAYou'll need a transformer rated for at least 100 kVA, and likely a standard size like 112.5 kVA. It's better to slightly oversize than undersize.

Transformer Inrush Current

Transformers have an inrush current on startup (much higher than the normal operating current). The overcurrent protection (circuit breaker or fuses) must be sized to handle this inrush without nuisance tripping, while still providing adequate protection for the feeder and transformer.

4. 208V Side Calculations Current Calculation (208V Side)

If the transformer is 480V delta to 208V wye, the current on the 208V side will be higher. To determine the load side current, divide the KVA of the transformer by the line voltage. I = (KVA1000)/(Volts1.732) I = (1001000)/(2081.732) I ≈ 277.6 ampsYou will need conductors rated for at least 277.6 amps.

Feeder Size on 208V Side

If you use the same size wire on the load side of the transformer as you use on the line side, it will be overloaded.

5. Important Considerations and Recommendations Licensed Electrician

This is not a DIY project. Working with 480V and transformers is inherently dangerous and requires specialized knowledge and equipment. Hire a qualified and licensed electrician. They are up to date with the NEC code and will ensure the project is properly installed.

Local Codes and Permits

Obtain all necessary permits and ensure the installation complies with all local and national electrical codes. Your electrician will handle this.

Overcurrent Protection

Properly sized circuit breakers or fuses are essential on both the primary (480V) and secondary (208V) sides of the transformer.

Grounding

A proper grounding system is critical for safety. The electrician will establish this per NEC requirements.

Transformer Location and Ventilation

Transformers generate heat. Ensure adequate ventilation and clearance around the transformer to prevent overheating.*

Coordination Study

For larger installations, a coordination study might be recommended to ensure the overcurrent devices operate in a coordinated manner, minimizing outages.

In summary


Hire a Qualified Electrician

This is the most important step.2.

Verify Load Requirements

Double-check the actual voltage and current requirements of your scoreboard.3.

Proper Calculations

Your initial calculations need to be reviewed and corrected. A qualified electrician will perform these accurately.4.

Adequate Wire Sizing

The 2/0 aluminum may not be adequate, especially if you're concerned about voltage drop.5.

Correct Transformer Sizing

Get a transformer sized appropriately for your load.

Next Steps (with your electrician)


Provide the electrician with the exact load details (voltage, current, power factor if available).2. Have them perform a complete load calculation and voltage drop analysis.3. Obtain necessary permits and approvals.4. Install the system according to the NEC and local codes.Disclaimer: This information is for general guidance only. Consult with a qualified and licensed electrician for any electrical work. Incorrect electrical work can lead to serious injury, death, or property damage. Flag for review