NEC220.87 Determining Existing Electrical Loads

May 19, 2023

In today's world, reliable and efficient electrical power systems are crucial for businesses and households alike. When it comes to providing top-notch electrical services, Site Electric Services is a trusted name in Solano County and its surrounding areas. One of the essential services we offer as part of our design services is performing powers system load studies that meet the NEC 220.87 requirements. In this blog post, we will explore the significance of this study, how it benefits clients and customers, and why Site Electric Services is the go-to provider for all your electrical needs.

The National Electrical Code (NEC) is a set of standards developed by the National Fire Protection Association (NFPA) to ensure the safe installation and operation of electrical systems. NEC 220.87 specifically addresses power system load studies, which are essential in determining the electrical demand and capacity requirements for a specific location, panel, or piece of equipment.

When installing new equipment such as electrical vehicle chargers, kitchen equipment, or other electrical loads in a commercial space it is often necessary to permit and provide drawings to the Authority Having Jurisdiction (AHJ) which is often the building department of county or city the facility is located in.

Site Electric Services owns our own metering equipment and provides onsite support to install temporary metering which meets NEC 220.87 requirements throughout Solano & Napa Counties and the cities of Vallejo, Napa, Fairfield, and Vacaville.

A power system load study involves assessing the electrical load on a facility to determine if the existing electrical infrastructure can support it or if upgrades are necessary. For many facilities using maximum demand data provided by the utility such as PG&E is sufficient for determining maximum demand on the panel or switchboard but for more complex and larger systems where loads are being added further down stream from the utility meter it may be necessary to install a temporary meter for 30 days to determine loading and peak demand.

NEC Article 220.87

The calculation of a feeder or service load for existing installations shall be permitted to use actual maximum demand to determine the existing load under all of the following conditions:

NEC 220.87


"The maximum demand data is available for a 1-year period.

Exception: If the maximum demand data for a 1-year period is not available, the calculated load shall be permitted to be based on the maximum demand (the highest average kilowatts reached and maintained for a 15-minute interval) continuously recorded over a minimum 30-day period using a recording ammeter or power meter connected to the highest loaded phase of the feeder or service, based on the initial loading at the start of the recording. The recording shall reflect the maximum demand of the feeder or service by being taken when the building or space is occupied and shall include by measurement or calculation the larger of the heating or cooling equipment load, and other loads that may be periodic in nature due to seasonal or similar conditions.

The maximum demand at 125 percent plus the new load does not exceed the ampacity of the feeder or rating of the service.

The feeder has overcurrent protection in accordance with 240.4, and the service has overload protection in accordance with 230.90.

Exception: If the feeder or service has any renewable energy system (i.e., solar photovoltaic systems or wind electric systems) or employs any form of peak load shaving, this calculation method shall not be permitted. "


Determining loading up front in your project is a crucial step in making sure you can achieve the goals you are aiming for in a cost effective and timely manner. For alterations to your facilities electrical facilities a load study is a great first step in making sure you will have enough capacity to support your new equipment and satisfy the requirements of the building officials in your jurisdiction.

When it comes to NEC 220.87 power system load studies in Solano County and nearby cities, Site Electric Services is the premier choice. With their team of highly skilled and experienced electricians and engineers, they offer comprehensive load studies tailored to the unique needs of each client.

Site Electric Services has a proven track record in providing top-notch electrical services. Their team of professionals stays updated with the latest NEC codes and regulations to ensure compliance and deliver accurate load studies.

Recognizing that each client's requirements are unique, Site Electric Services offers personalized solutions based on the specific demands of your facility. Their in-depth load studies consider factors such as equipment usage, peak demand periods, and future growth.

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