Okay, let's break down this load calculation and discuss balancing options.1. Applicability of 220.83(A) - Optional Method for Additional Load in Existing Dwelling Unit(s)

Yes, you can use 220.83(A) if you meet the following conditions and deem it advantageous: Existing Dwelling Unit(s)

The building was previously multiple dwelling units, and now it's being converted into a single dwelling unit (a penthouse). This likely satisfies the "existing dwelling unit(s)" part.

Overcurrent Protective Devices

The existing service equipment has overcurrent protective devices adequate for the load. You will have to ensure the existing service equipment is large enough to handle the calculated load after applying the demand factors in 220.83.

Adequacy

You have to calculate your calculated load using the standard method (220.82) or the optional calculation method and compare it to the load used using 220.
83. If the load calculated is smaller, then this is applicable to be used.Important Caveats About 220.83:

Don't blindly assume it will result in the lowest calculated load. It depends on the magnitude of the existing load compared to the new load. You must calculate both using 220.82 first to confirm the result. Inspect the existing service equipment thoroughly. Ensure it's in good condition, has sufficient ampacity for the calculated new load. Verify existing wiring. Inspect the wiring of the existing branch circuits and feeders. Ensure the wiring is in good condition and large enough to handle the new load. Local AHJ: Be prepared to justify your use of 220.83 to your local Authority Having Jurisdiction (AHJ). They have the final say.2. Calculating the New Load (Assuming You Will Use the Optional Method)Here's how you'd approach the calculation using the optional method in 220.83(A) and adding the HVAC at 100%:

Step 1: Calculate the Existing Load. You'll need to estimate the existing general receptacle and lighting load. Since this was formerly 5 apartments, you can reasonably assume they had a certain load. Here's how I would go about this part: Option 1: Record actual load - The code specifically allows you to record the actual maximum kilowatt demand over a 1-year period if available and that could be your starting point. Option 2: Assume existing load - Calculate this using 220.12 which is 3VA per square foot.

Step 2: Calculate the Additional Load.

Kitchen Equipment

Dishwashers: 2 1200W = 2400W Ovens: 2 6000W = 12000W Refrigerators: 3 1800W = 5400W Washer/Dryers: 2 2100W = 4200W Microwaves: 3 1000W = 3000W Instant Hots: 2 1300W = 2600W

Total Kitchen Equipment: 29,600W

Master Bathroom

Steam Showers: 2 2400W = 4800W Electric Fireplace: 1500W Jacuzzi: 1800W

Total Master Bathroom: 8100W

Total Additional Load (Kitchen + Bathroom): 37,700W

Step 3: Apply Demand Factors (Using 220.83(A)). First 8 kVA or less of additional load = 100% demand factor Remainder of additional load exceeding 8 kVA = 40% demand factor. First 8000W = 8000W Remainder 29,700W X 40% = 11,880W Total: 8000W + 11,880W = 19,880W Step 4: Add HVAC Load. Since you are not touching or making any changes to the HVAC system, you will have to add the HVAC load at 100% You need to determine the existing HVAC load by reviewing the nameplate data on the existing equipment (air conditioners, heat pumps, furnaces, etc.). Let's say, as an example, the total HVAC load is calculated to be 15,000W. Step 5: Calculate the Total New Load. Existing Load (from Step 1) + Additional Load (from Step 3) + HVAC Load (from Step 4) Example: 25,000W + 19,880W + 15,000W = 59,880W Step 6: Convert to Amps. I = P / (V PF √3) (For 3-phase) I = P / (V PF) (For single-phase) Assuming a single-phase, 208V service and a power factor (PF) of 0.9 (a reasonable assumption), then I = 59,880W / (208V 0.9) = 319.5 ATherefore, based on these assumptions and using the optional calculation, the estimated load is approximately 319.5 amps.Important Note

This is a simplified example. You must perform a thorough calculation using the actual wattage ratings of all equipment, considering the existing load, and using a power factor appropriate for your installation.

3. Balancing the Load Across Existing Panels and Potentially Adding New Panels

You have a few options to balance the load and ensure that the total load on any individual panel doesn't exceed its 100A rating. Here's a breakdown: Option 1: Re-Distribute Existing Circuits The first step is to carefully map out all existing circuits and their loads. You will need to identify the circuits that were used to supply the apartments. Move circuits from heavily loaded panels to those with more capacity. Try to balance the load across all three phases (if you have a 3-phase panel - less of a concern with primarily single-phase loads, but still good practice). This can be labor-intensive, but it's the most cost-effective option if you have enough spare capacity in some panels. Option 2: Convert Some 120V Circuits to 240V Appliances like ovens, dryers, and some water heaters can be wired for 240V. Doing so reduces the current draw on each leg, freeing up capacity on the panel. Important: This requires rewiring the appliance's circuit with appropriate 240V wiring and breaker. This can be helpful, but requires careful planning and consideration of the appliances' voltage ratings.

Option 3: Add Subpanels This is often the best solution if the existing panels simply cannot handle the new load, even after re-distribution. Install one or more subpanels fed from the main service. Distribute the new equipment circuits across these subpanels, ensuring balanced loading. This is the most expensive option, as it requires new panels, breakers, wiring, and labor. However, it provides the most flexibility and ensures the electrical system is not overloaded.

Option 4: Upgrade the Main Service If you're consistently finding the calculations are close or exceeds the main service, it may be necessary to upgrade the main service.

Balancing Best Practices



Use a Load Calculation Worksheet

There are many available online or from electrical supply companies. These help you systematically account for all loads.

NEC Code Compliance

All work must comply with the National Electrical Code (NEC) and any local amendments.

Professional Consultation

Crucially, I strongly recommend consulting with a licensed electrical contractor. They can perform accurate load calculations, assess the existing electrical system, and recommend the most appropriate solution for your specific situation. They'll also be able to pull the necessary permits and ensure the work is done safely and to code.

Consider Future Load Growth

Design the electrical system with some extra capacity to accommodate future load increases. This is particularly important in a high-end penthouse where additional appliances or features might be added later.

In summary: You can likely use 220.83(A) if the calculations bear out. Adding HVAC load at 100% is correct. Balancing the panels can be achieved through redistribution, converting some circuits to 240V, or adding subpanels. Consult a licensed electrician for a comprehensive assessment and solution. Flag for review