Okay, let's break down your plan and see if it jives, addressing each part step-by-step. It's good you're thinking this through carefully, especially with high voltage and current involved.

Important Disclaimer

I am an AI and cannot provide electrical advice. This information is for discussion and conceptual understanding only. All electrical work should be performed by a qualified and licensed electrician following all applicable codes and regulations. Incorrect wiring can lead to fire, injury, or death.

1. The 480V Transformer Plan Your Thinking is Good

You're correct in that stepping up voltage requires more current on the input side than you get on the output side. The power (VA) remains (relatively) constant, minus any transformer losses.

Calculations and Concerns



VA Calculation

Your biggest load is 54A at 480V. This equates to: 54A 480V = 25,920 VA or roughly 26 kVA. This is the MINIMUM transformer size you should consider. It's always best to upsize slightly for safety and future needs (e.g., a 30 kVA or 37.5 kVA transformer).

Primary Current (120/208V Side)

To get 26kVA on the secondary, the primary must provide at least that much. Using the 208V input voltage (since that's what you have available), the primary current would be: 26,000 VA / 208V = 125A (approximately). You're on the right track. BUT keep in mind the 125A number is theoretical based on no losses, in reality the losses in a transformer typically adds about 10%, putting you close to 138A

125A Breaker and 2 AWG Wire

This is where things need careful scrutiny. 2 AWG wire is generally NOT rated for 125A. According to the NEC (National Electrical Code, in the US), you need to consult Table 310.16 for allowable ampacities. Even with certain insulation types and conduit conditions, 2 AWG is often rated closer to 95A-115A (at 75°C termination rating, which is common). You'll need a larger conductor. A good rule is to never load a breaker at it's total value, sizing a breaker up for a bigger wire is the better idea.

60A Load Side Main

This is also an issue. Your 54A load is close to the limit of a 60A breaker. While you might get away with it for short, 1-minute tests, it's cutting it extremely close and could lead to nuisance tripping. If the equipment requires start-up current then this is too small.A 100A main is safer, this gives you some breathing room, as well as some headroom on your 480 side in case the equipment being tested pulls more amps. The idea is to not work your equipment so hard.

Transformer Location

10 feet away and in sight is generally acceptable from a practical standpoint, but make sure it complies with all local electrical codes regarding clearances, ventilation, and protection from physical damage.

Revised Suggestions for the 480V Setup


Transformer Size

Choose a 30 kVA or 37.5 kVA transformer rated for 208V primary to 480V secondary.
2.

Primary Breaker and Wiring

Calculate your maximum primary current based on the transformer VA rating and the 208V primary voltage. Then, choose a breaker and wire size that can safely handle that current plus a safety margin (at least 25%). You'll likely need a breaker larger than 125A, and definitely larger wire than 2 AWG. Possibly 1/0 or 2/0 depending on the type of wire and termination temperature rating.3.

Secondary Breaker and Wiring

A 60A breaker for a 54A load is too close. Upgrade to at least 70A or 80A, and size the wiring accordingly.4.

Calculate all Volt Drop

The 10ft distance is minimal, but still important to factor into the volt drop calculations. You'll need to factor in wire material (Cu or Al), wire gauge and expected load.

2. The 208V-to-240V Transformer Plan Reverse Connection

Yes, it is possible to use a transformer "backwards" to step up voltage, provided the voltage ratings match. However, there are nuances.

Considerations



VA Rating

A 15 kVA transformer should be adequate for testing purposes, assuming the equipment you're testing at 240V doesn't exceed that VA rating (amps volts).

Voltage Taps

Some transformers have voltage taps. Check the transformer specifications to see if they're suitable for your application when connected in reverse.

Neutral Considerations

When reversing a transformer, the neutral (if present) on the secondary (240V) side will become a grounded conductor on the primary (208V) side. This is important for grounding and bonding.

Polarity

Ensure proper polarity is maintained when reversing the connections.

3. Overall System Considerations Existing 200A Panel



Load Calculation

Before adding anything, perform a comprehensive load calculation on your existing 200A panel to determine if you have enough capacity. Include all existing loads (lighting, fridges, etc.) plus the expected loads from the two new transformers. Adding two large transformers could easily overload your panel.

Service Upgrade

If your load calculation shows that you're exceeding 80% of your 200A panel's capacity, you'll likely need to upgrade your service to a larger amperage.

Short-Circuit Current Rating (SCCR)

Make sure all components (transformers, panels, breakers, etc.) have adequate Short-Circuit Current Ratings for your location. This is a crucial safety consideration.

Grounding and Bonding

Proper grounding and bonding are essential for safety. Consult with a licensed electrician to ensure your grounding system meets all code requirements.

Local Codes

Electrical codes vary by location. Your plan must* comply with all local codes and regulations. A qualified electrician will be familiar with these codes.

Key Takeaways and Recommendations


Hire a Qualified Electrician

This is not a DIY project. Due to the high voltages and currents involved, it's critical to hire a qualified and licensed electrician to design and install the system.2.

Perform a Thorough Load Calculation

Don't guess. Calculate the total load on your existing panel before adding anything new.3.

Size Transformers Appropriately

Choose transformers with adequate VA ratings and consider upsizing slightly.4.

Proper Wire and Breaker Sizing

Calculate wire and breaker sizes based on the actual current draw, considering safety margins and code requirements. Never undersize wires or breakers.5.

Adhere to Electrical Codes: Ensure all work complies with all applicable electrical codes and regulations.By following these steps and working with a qualified electrician, you can ensure a safe and reliable electrical system for your friend's industrial shop. Flag for review