Paul from Seattle. Quick practice note for newer members. Always confirm the demand interval on every new commercial engagement before you calculate anything. I discovered this the hard way when I built a full analysis assuming 15-minute intervals and the utility in that territory used 30-minute intervals. My calculated peak demand was wrong and I had to redo three months of work.
Why I always check the demand interval on new engagements
Dave from Charlotte. Good reminder. Where do you find the interval length reliably?
Paul again. Three places: the tariff schedule under metering provisions, the utility's meter data management system if you can access it, or the interval data file itself — the timestamps tell you the interval length directly if you look at the spacing between rows.
Maria from Austin. Does the interval length change the total energy calculation or just the demand?
Paul here. The interval length affects only demand calculations. The energy in kWh is the same regardless because you are summing all the intervals. But the kW demand reading is directly affected — a 30-minute interval averages over twice as long and will generally show a lower peak than a 15-minute interval for the same load.
Phil from Denver. This is especially important for clients with brief sharp spikes like motor starts or welding equipment. A 15-minute interval can capture a spike that a 30-minute interval would partially obscure. Knowing the interval tells you how exposed or protected the client is to transient peaks.