30 Day Electrical Load Studies | Why Are They Necessary?

Why Are Load Studies Necessary? 

When providing electrical contractors with load studies for a new installation, end customers often fail to understand why they are necessary. After all, the branch circuit panel has spare breakers.

Typical Brach Circuit Panelboard with Load | Load Studies
Typical Branch Circuit Panelboard with Loads

So why can’t the electrician hook up the new load?

Let us break it down for you.

Load Studies | Understanding NEC Requirements

Most customers aren’t aware that the National Electrical Code (NEC) requires a load study. Load studies protect both people and properties from overloads—specifically, section 220.87 (Determining Existing Loads).

The NEC Code 220.87 specifies that load calculations for existing equipment shall use actual measured loads to determine a panel’s total permissible load. This section requires the electrical load data of a panel for one year. Consequently, this effectively delays any retrofit construction. 


An exception exists, permitting electrical contractors to make a precise load survey of the panelboard. 

For example: 

What if the maximum demand data for one year isn’t available? 

Maximum demand refers to a measure of average power demand over 15 minutes. 

In that case, the calculated load shall be permitted based on the maximum demand continuously recorded over a minimum 30-day period. 

These 30 days are measured 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).

Meanwhile, taking recordings from an occupied building or space ensures it will reflect the feeder or service’s maximum demand.

The Recording Includes: 

  • The measurement or calculation of the larger heating or cooling equipment load
  • Other loads that may be periodic due to seasonal or similar conditions

Responsible electrical contractors update the panel schedule each time a load is added or removed( with the watts per phase for each load). Updating the panel schedule consistently helps avoid current unbalance between phases as well as overloads.

Typical Panel Schedule | Load Studies
Typical Panel Schedule

APT Can Help

APT understands the difficulty of managing multiple customer sites running numerous load studies simultaneously when the study doesn’t update the panel schedule.

Load Studies Voltage Scale

As an electrical contractor service provider, we’re able and willing to keep you focused on what you do best. APT does power monitoring and studies every day. It’s what we do best. Put us to work. We manage load study meter inventory, handle calibration, and convert load study data into updated panel schedules.

Let us be there to support you. Don’t bear the load on your own.

Andrew E Taylor, PE CEO at APT