You're right to be careful. Converting a 240V high-leg delta to 480V 3-phase is possible with a transformer, but it's not straightforward and has some critical considerations. Let's break down the options

1. Delta-Delta Transformer: This is the Correct General Approach
How it Works

A delta-delta transformer takes a 3-phase delta input (your 240V high-leg) and outputs a 3-phase delta voltage (480V). The "delta" configuration on both sides is important because your incoming service is delta, and most 480V equipment expects a delta supply.

Important Considerations and Potential Issues



High-Leg Handling

This is crucial. The "high leg" (also known as the "wild leg" or "stinger leg") is typically 208V to ground (rather than the 120V on the other two legs in your 240V delta system). A standard delta-delta transformer

will pass the high leg characteristic through to the 480V output. This means one leg of the 480V output will have a higher voltage to ground than the other two. You absolutely must properly label this leg and ensure the equipment being powered is designed to handle this. This is where some confusion and misapplication can occur. Sizing

Calculate the kVA (kilovolt-amperes) needed. Your equipment draws 6 amps at 480V 3-phase. kVA = (Volts x Amps x √3) / 1000 kVA = (480V x 6A x 1.732) / 1000 kVA ≈ 5 kVA Therefore, you need at least a 5 kVA transformer. It's generally a good idea to slightly oversize (e.g., a 7.5 kVA or 10 kVA) to allow for future load growth and to avoid stressing the transformer.

Isolation

A delta-delta transformer provides isolation between the input and output. This is generally a desirable safety feature.

Vector Group

The vector group (e.g., Dd0, Dd6) describes the phase shift between the primary and secondary windings. For most applications, it doesn't matter significantly, but a Dd0 is common and often the easiest to find.

Specifically Mention High-Leg Delta Input

When you order the transformer,

explicitly state that it will be used with a 240V high-leg delta input. This ensures the transformer is designed to handle the voltage characteristics. A supplier familiar with high-leg systems will know what to provide.2. Buck-Boost Transformer on the High Leg: Not Appropriate Why it's wrong

A buck-boost transformer is designed to slightly adjust voltage (e.g., boost 208V to 240V, or buck 240V to 208V). It is

not designed to create a 480V 3-phase supply from a 240V high-leg. Furthermore, buck-boost transformers are usually single-phase devices. You would need a very complex (and ultimately impractical and unsafe) arrangement of multiple buck-boost transformers to even attempt to do what you want, and even then, it wouldn't be a proper 3-phase conversion. Do not attempt this.Important Safety and Code Considerations



Licensed Electrician Required

This is not a DIY project. A qualified and licensed electrician must perform the installation. Incorrect wiring can be dangerous and violate electrical codes.

Grounding

Proper grounding is absolutely essential. The electrician will need to ensure that the transformer and the new 480V circuit are properly grounded according to the National Electrical Code (NEC) and local codes.

Overcurrent Protection

Install appropriately sized circuit breakers or fuses on both the input and output of the transformer to protect it and the equipment.

Labeling

Clearly label the transformer and the 480V panel/disconnect as being derived from a 240V high-leg delta system, especially indicating the high leg.

Permitting and Inspection

Check with your local building department regarding permitting and inspection requirements for electrical work.

Steps to Take


Consult with a Licensed Electrician

Get a qualified electrician involved immediately. They can assess the existing service, calculate the required transformer size accurately, and ensure a safe and code-compliant installation.2.

Contact a Transformer Supplier

Work with a reputable transformer supplier who understands high-leg delta systems. Provide them with the input voltage (240V high-leg delta), the desired output voltage (480V 3-phase delta), and the load requirements (6 amps, or the calculated kVA).3.

Choose the Right Transformer

Select a delta-delta transformer that is specifically designed to handle a high-leg delta input and provide the required kVA.4.

Install and Test

The electrician will install the transformer, connect the wiring, and thoroughly test the system to ensure it is working correctly and safely.

In Summary:

A delta-delta transformer is the correct type of transformer to convert 240V high-leg delta to 480V 3-phase. However, you must* select the transformer carefully, paying close attention to its suitability for high-leg systems and ensure the high-leg characteristic is safely and properly managed and labeled on the output. A buck-boost transformer is not appropriate for this application. Engage a licensed electrician for the installation. Flag for review