Okay, Howard, let's break down the load diversity concept and how it applies to your situation. You're right, there isn't a specific "load diversity calculation" explicitly laid out in the NEC like the demand factors for dwelling units. Diversity is about estimating how much of the connected load will actually be in use simultaneously.

Understanding Load Diversity

Load diversity is the principle that not all electrical loads will be running at their maximum capacity at the same time. It's a realistic assessment of how the space will actually be used, rather than assuming everything is drawing full power all the time. This allows for a smaller service than if you simply added up the nameplate ratings of every piece of equipment.

Why the Power Company Asks About Diversity

The power company wants to understand your realistic load demand. They use this information for planning their distribution system and ensuring they can supply the power needed to the area. Overestimating load can lead to unnecessary infrastructure investment. Underestimating can cause brownouts or equipment damage.

Applying Diversity to Your Vanilla Box

Because it's a vanilla box, determining the actual load is inherently challenging. You have limited information about the eventual tenant's specific equipment. Here's a suggested approach:1. NEC Minimums are Your Starting Point, But Not Your Ending Point



Lighting

You've already calculated this at 4500 VA. This is good.

General Purpose Receptacles

You've allocated 6000 VA. Per NEC Article 220.14(I), general-use receptacles are typically calculated at 180 VA per receptacle. So 6000VA/180VA = 33 Receptacles. While the NEC doesn't have demand factors for this type of commercial space, it also doesn't limit your ability to apply rational engineering judgement based on the intended use.
2.

HVAC Load: Critical Information Get the actual nameplate ratings (VA or kW, along with voltage) for the HVAC equipment. This is absolutely crucial. The HVAC system is often the single largest load in a commercial space.3. Consider the Potential Tenant (If You Have Any Idea)

Office Space? Diversity might be higher. Not every computer, printer, and coffee maker will be running at full blast simultaneously. Retail Space? Consider display lighting, point-of-sale systems, refrigeration (if applicable), and potential specialized equipment. Restaurant/Food Service? Diversity will likely be lower because cooking equipment often operates simultaneously and at high demand. Light Manufacturing/Workshop? Diversity could be low depending on the type of machinery.4.

Applying Judgment and Justification HVAC

The HVAC will likely run a substantial portion of the time, especially during peak heating/cooling seasons. Therefore, apply a lower diversity factor here. I would suggest a demand factor of 75-100%.

Lighting

The lighting will generally be on when the space is occupied, but not always at 100%. Consider a diversity factor of 80-90%.

General Purpose Receptacles

This is where judgment is most important. If the tenant is likely to be an office, and the receptacles are primarily for computers, monitors, and small peripherals, a diversity factor of 50-70% might be reasonable. This is assuming not every receptacle is fully loaded simultaneously. If the tenant is likely to have equipment that uses a higher number of receptacles for more continuous use (retail, workshop), consider a diversity factor closer to 80-90%.

Explain Your Assumptions

In your documentation to the power company, clearly state the assumptions you made about the likely tenant type and how you arrived at your diversity factors. This is very important.

Example Calculation (Illustrative)

Let's assume you get HVAC information and it's 20,000 VA. Let's also assume it is most likely to be an office space. HVAC

20,000 VA 0.85 = 17,000 VA (85% demand)

Lighting

4,500 VA 0.85 = 3,825 VA (85% demand)

Receptacles

6,000 VA 0.65 = 3,900 VA (65% demand)

Total Estimated Load

17,000 + 3,825 + 3,900 = 24,725 VA

Calculating Amps



Single-Phase (Hypothetical)

24,725 VA / 240 V = 103 Amps (This is just for comparison)

Three-Phase (Your Actual Situation)

Apparent Power (VA) = √3 V_line-to-line I_line I_line = VA / (√3 V_line-to-line) I_line = 24,725 VA / (√3 240 V) = 59.4 Amps per phase (approx.)

Service Size Your 200 Amp, 3-Phase service likely provides plenty of capacity for the base building. However, be sure to take into account the panel capacity. Your main breaker or fuses shouldn't exceed the rated capacity of the distribution panel. If you are subdividing one service into two, you will need to ensure that the existing service to the building is large enough to carry both new spaces. You may need to upgrade the service.

Key Considerations and Actions



Documentation

Thoroughly document your load calculations, your assumed tenant type, and your rationale for the diversity factors you used.

Communication with the Power Company

Discuss your approach with the power company. They may have guidelines or preferences for how they want these calculations presented. They also might have experience with similar buildings in the area.

Future-Proofing

While you want to avoid oversizing, consider potential future needs. It might be wise to include some extra capacity (within reason) in your load calculation to accommodate unexpected loads from the tenant.

Flexibility

Be prepared to adjust your calculations if you get more information about the eventual tenant's needs.*

Local Codes

Double-check for any local amendments to the NEC that might affect your calculations.

In conclusion: You won't find a simple formula for diversity. It's a judgment call based on your understanding of the space, potential uses, and a healthy dose of common sense. The HVAC load is crucial, and clearly documenting your assumptions is key. Discuss your approach with the power company to ensure it meets their requirements. Good luck! Flag for review