Existing Building per Utility Data — NEC 220.87 (2023)

Evaluate available electrical service capacity using recorded utility demand data.

Three Main Requirements

  1. Use 1 year of maximum-demand data. If unavailable, at least 30 days of continuous monitoring may be used, based on the highest 15-minute average kW. The building must be occupied during the monitoring period, and seasonal or periodic loads must be considered. This exception is not allowed with solar, wind, or peak-load shaving.
  2. Verify service capacity:
    125% × Existing Maximum Demand + New Load ≤ Service/Feeder Capacity
  3. The existing service/feeder must have proper overcurrent and overload protection.
1Project & Utility Info
2Utility Data
3Load Analysis
4Add New Loads
5Results

Project & Utility Information

Enter your 5-digit ZIP code and we’ll find your electric utility.

Existing Electrical Service

A
Example: 100, 150, 200, 400
Please enter a valid service rating greater than zero.

Utility Demand Data

Get the maximum-demand information from your utility bill or online utility account and enter it below.

1

Select Data Method

30-day exception: The building must be occupied during monitoring, seasonal or periodic loads must be considered, and this exception cannot be used with solar, wind, or peak-load shaving.
2

Enter Maximum Demand

Maximum Demand Value
kW
Select the same interval shown in your utility data.
Enter the highest maximum demand shown in your utility data.
Calculated Maximum Demand: — kW
Please enter a valid demand value greater than zero.
How to find this value
Check your utility bill or online account for “Maximum Demand” or “Peak Demand.”

If shown in kW, enter the value directly.

If shown as interval energy in kWh, ZigTech converts it automatically:
15 min: kWh × 4 = kW
30 min: kWh × 2 = kW
1 hour: kWh × 1 = kW