You're right, the 20 individual transformer setup does sound unnecessarily complex and expensive. Let's break down the "why" and then tackle the pricing.

Why the Individual Transformers Design is Probably Suboptimal



Cost

As you pointed out, the cost of 20 transformers, plus the labor to install and wire each one at 20 feet high, will likely be far more than a single, larger transformer and a beefier busway.

Complexity

20 transformers adds significant complexity to the system. More points of failure, more components to inspect and maintain.

Space

Even small 15kVA transformers take up space. 20 of them will require significant overhead clearance and possibly require additional structural support.

Efficiency

Each transformer has losses. While a single larger transformer will also have losses, the cumulative losses of 20 smaller units may be higher, depending on transformer efficiency curves. It would require a more detailed energy analysis to verify.

Potential Upsides (although unlikely to outweigh the negatives)



Redundancy

If one transformer fails, only one charger is affected. However, a well-designed system with a single transformer could incorporate redundancy as well.

Voltage Drop

With individual transformers, voltage drop to each charger might be slightly better than a long run from a single transformer. However, proper busway sizing and voltage drop calculations should mitigate this.

Load Diversity

The original designers may have anticipated that the chargers would not draw their maximum power at the same time. By using smaller transformers, they can reduce the overall system demand and minimize the need for a larger transformer.

Possible (but unlikely) Reasons for the Original Design (you'd need to confirm with the engineer)



Existing Infrastructure Limitations

Perhaps the existing service or panelboard only has capacity at 480V, and it was easier to tap into that than to upgrade to a higher voltage service. Unlikely, but possible.

Manufacturer Preference/Bundle Deal

The design might be driven by a specific manufacturer who offered a package deal on these smaller transformers.

Misunderstanding of EV Charger Requirements

Some EV chargers might require a dedicated transformer for isolation or specific voltage requirements. However, most modern chargers can operate directly on 240V from a properly sized circuit.

Load Diversity

As mentioned before, if the engineers think you can get away with a smaller transformer and smaller busway, they would have used individual transformers to limit the system load.

The Better Approach: Single Transformer, Larger Busway (or Panel)

A single transformer at the head of the busway, stepping down 480V to 240V, is almost certainly the more economical and practical solution. This would require:1.

A larger transformer

Calculate the total kVA load of all 20 chargers (15kVA 20 = 300kVA). Factor in any diversity you anticipate (unlikely all chargers will be at full load simultaneously). Size the transformer accordingly.2.

Larger busway (or Panel)

The busway will need to carry the full load of the 20 chargers, plus any additional capacity for future expansion. A panelboard feeding individual circuits can be easier to expand in the future.

Busway Pricing Ballpark (with caveats!) Disclaimer

Busway prices fluctuate wildly based on current metal prices (especially copper), manufacturer, lead times, and your location. The following is a very rough estimate only! Obtain firm quotes ASAP.

400A Copper Busway (3-Phase, 3-Wire + Internal Ground)

You can expect to pay

around $80-$120 per foot for materials only. (Keep in mind these prices have gone up, and vary widely based on material cost). This is a very wide range, but it gives you a starting point. It does not include installation labor, hangers, elbows, end closures, or the bus plugs. Bus Plugs (30A)

Expect to pay

$300 - $500+ per plug, depending on the brand and features (fuses, breakers, etc.). Important Factors Affecting Price



Copper vs. Aluminum

Aluminum busway is cheaper but has limitations in terms of ampacity for a given physical size.

Manufacturer

There are several reputable busway manufacturers (e.g., Siemens, GE, Eaton/Cutler-Hammer). Get quotes from multiple vendors.*

Lead Time

Longer lead times might allow for better pricing (if the supplier can lock in material costs). Shorter lead times often mean higher prices due to material scarcity.

Actionable Steps for You


Push for Firm Quotes

Keep hounding your suppliers for firm quotes on the busway and bus plugs. Emphasize the urgency of the situation.2.

Present the Alternative Design to the GC and Engineer

Clearly outline the cost savings, reduced complexity, and potential efficiency gains of the single transformer/larger busway approach. Include rough pricing for both options.3.

Get Transformer Quotes

Get quotes for a properly sized transformer (e.g., 300kVA or higher, depending on load calculations and diversity).4.

Consider a Panelboard Option

Instead of busway, consider a large panelboard at the head of the circuit. This may have cost or flexibility advantages.5.

Document Everything: Keep meticulous records of all communication, quotes, and design changes.Good luck! This is a situation where clear communication and a well-documented cost analysis can make a huge difference. Flag for review