Load Study with DranXperT

DranXperT Survey Study: officially published by Dranetz

Introduction on this load study

The National Fire Protection Association (NFPA) publishes NFPA 70, the National Electric Code (NEC). The NEC is the US reference for the safe installation of electrical systems. Although the NEC is not mandated by the US federal government, most states and/or municipalities in the US require compliance with NEC requirements.

NEC article 220 is for branch circuit, feeder, and service calculations and section 220.87 covers the requirements to determine existing loads. Compliance with NEC 220.87 is a requirement to determine available capacity when adding loads. For this purpose a load study with DranXperT was executed.

NEC 220.87 requirements

NEC 220.87 states that it is permissible to use the actual maximum demand when determining existing loads, but there are conditions.

The first condition is that the maximum demand data is available for 1 year. Practically speaking, unless the facility has existing branch circuit or other monitoring, 1 year of demand data may only be available at the utility service from utility billing.

There is an exception if maximum demand data is not available for 1 year – the calculated load can be measured at the feeder or service. Such a measurement requires a minimum 30-day load study by a power logger measuring the demand averaged over a 15-minute period. The load study must be taken while the space is occupied and include
measurements or calculations of the heating and cooling equipment (whichever is larger). Refer to NEC 220.87 for specific details.

Another condition is that 125% of the maximum demand plus the new load does not overload the circuit. The requirements for overload protection are covered elsewhere in the NEC.

Configuring the measurement device for the load study

For this study a DranXperT device has been used. Configuring DranXperT for a NEC 220.87 load survey is simple, and the settings are virtually identical to any other load study. It is important that you do the following to meet the requirements of NEC 220.87:

• On the Survey Setup page set the Demand Interval to 15 minutes and the Journal Interval to 900 seconds (15 minutes). Doing so will program DranXperT to record the 15-minute average information required by NEC 220.87.
• On the Instrument Setup page make sure that the Max DB File Seconds setting is set to the default of 31 days (or longer). This will meet the requirement of a minimum 30-day survey, and the data will recorded in one data file.

Determining the maximum demand

Determining the maximum demand or amperage is as simple as loading the data file into Dran-View XP (or Pro & Enterprise) and reading the maximum values for demand and amperage directly off the 30+ day trend plot.

In the right, the maximum demand and amperage occurred on June 7, 2021. The maximum demand was 260Kw and the maximum amperage was 891A on phase C. This is the information required to determine the available capacity for additional loads.