Transcript
What Is a Load?
Before we get into load diversity, let’s make sure we’re all on the same page about what a load actually is. A load is anything that consumes electricity: a light bulb, an air conditioner, a factory motor. If it’s plugged in and drawing power, it’s a load.
Every one of those devices draws current. That’s the flow of electricity through the wire, and the sum of all of them determines the total load on the circuit.
Now, here’s the thing: not all loads behave the same electrically. Some draw current very smoothly. A space heater, for example, pulls in current in a clean, predictable wave. But other devices, particularly ones with internal electronics like LED bulbs, computer power supplies, and variable frequency drives or VFDs, which are used to control motor speed, these all draw current in choppy, irregular patterns. That distinction is gonna matter a lot when we get to harmonics, so keep that in the back of your mind.
What Is Load Diversity?
In the simplest terms, it describes the fact that different customers draw power in different amounts at different times and with different electrical characteristics.
Think about it this way. A neighborhood of homes and a strip mall might share the same utility feeder. That’s the circuit that delivers power from the substation, but their electrical behavior is very different, and that variety is generally a good thing.
When customers don’t all demand peak power at the same moment, the utility can serve more customers without overwhelming its infrastructure. But when that diversity decreases, when too many customers peak at once, or when a circuit is dominated by one type of load, the power quality can suffer for everyone on that circuit.
Residential vs. Commercial Load Patterns
So let’s look at how residential and commercial customers actually use power because the patterns are almost opposite. A typical residential neighborhood is quiet overnight. You get a morning bump as people wake up, showers, coffee makers, hair dryers. Then it dips during the workday when most people are away. The big peak comes in the late afternoon and evening. Families come home, the air conditioning is cranking, dinner’s being cooked, and screens are on in every room.
Commercial facilities are almost the mirror image. They ramp up in the morning as businesses open, sustain heavy usage all through the business day, lighting, HVAC, elevators, computers, and then drop off sharply in the evening when everyone gets home.
You can see it clearly in this chart. The residential curve, the blue line, peaks in the evening, while commercial, the orange one, peaks midday. And that right there is load diversity in action. When these two customer types share a feeder, their peaks naturally stagger. One is winding down as the other ramps up.
Peak Coincidence
So every customer has a peak demand, a maximum amount of power they draw at some point during the day. But those peaks rarely all happen at the same time. We just saw that. Residential and commercial peaks land at completely different times of the day.
That staggering means the combined peak on a shared feeder is much lower than what you’d get if everyone peaked at once. This figure shows it side by side. On the left, you’ve got three customers with staggered peaks. The combined load, the black line, stays relatively moderate because their peaks come and go at different times.
On the right, those same three customers all peak at the same time. Look at that combined spike in red. It’s dramatically higher. That’s a coincident peak, and that’s where things start to get stressful for the electrical system.
So what causes this? It could be extreme weather, a scorching afternoon where both commercial cooling and residential air cooling are both running full blast in the same window. Or it can simply be a lack of diversity on the circuit, a feeder that only serves one type of customer.
How Coincident Peaks Affect Voltage
So coincident peaks are where power quality problems begin. Let’s talk about what actually happens to the power when you get a coincident peak.
Voltage is the electrical pressure that pushes current through the wires. No wire is perfect. Some energy is always lost along the way. That loss is called voltage drop, and the more current that’s flowing, the greater the drop.
So during a coincident peak, you’ve got high current, which means more voltage drop along the feeder. Customers near the substation might not notice much, but customers at the far end of the line, they see their voltage sag. Lights could dim, motors slow down, and could end up even drawing more current to compensate, which makes the problem worse.
You can see in this diagram under light load, that’s the solid green line, voltage stays comfortably within the acceptable range, which is plus or minus five percent of nominal per the ANSI C84.1 standard. But under heavy coincident load, the red line, voltage at the end of the feeder drops below that acceptable limit.
Now, the flip side is also true. During very low demand, say, 3:00 AM on a mild spring night, there’s very little current flowing, so very little voltage drop, and the voltage can actually creep above its intended level. Utilities manage this balancing act with specialized equipment designed to keep voltage steady. But that equipment is tuned for expected patterns. When coincident peaks exceed what was planned for, the system’s ability to hold voltage within limits gets tested.
Harmonics and Load Diversity
So now let’s talk about harmonics, and this is where that distinction between smooth and choppy loads comes back into play. The power system delivers electricity as a smooth wave cycling 60 times per second. That’s 60 Hz or 50 Hz in some parts of the world.
Harmonics are distortions that ride on top of that wave as whole number multiples of the base frequency, two times, three times, four times, and so on, warping its shape. So look at the difference here. On the left, you have a mostly clean 60 Hz waveform, a nice smooth sine wave. Now on the right, you can see what happens when harmonics are present. The rippling along the peaks, that’s a telltale sign of harmonic distortion.
So where do harmonics come from? Any device that draws current in a non-smooth way, what we call a nonlinear load, injects harmonics back into the system. LED bulbs, computer power supplies, VFDs, all of these. Individually, each one contributes a small amount, but they all add up.
So here’s where load diversity plays an interesting role. Different types of nonlinear loads produce different harmonic patterns. When those different loads share a feeder, their harmonics can actually partially cancel each other out, and that’s a hidden benefit of having a diverse load mix.
But when the diversity is low, say you’ve got a circuit that’s all residential or dominated by a single large commercial customer, similar loads produce similar harmonics, and they stack up instead of offsetting. The result is elevated total harmonic distortion, or THD, which can overheat transformers, trip breakers, and shorten equipment life.
Applying Load Diversity to Power Quality Investigations
So how does all of this apply in the real world? For anyone investigating a power quality complaint, understanding load diversity on the circuit is a critical first step. The key questions are straightforward.
- Is the circuit diverse or uniform? A mix of customer types benefits from natural diversity. A single type does not.
- Are coincident peaks driving voltage issues? If complaints cluster during specific times of day or specific weather conditions, coincident peaking may be the culprit.
- Are harmonics accumulating? If THD is elevated, a lack of diversity and the cancelization it provides could be a contributing factor.
And knowing those answers changes what you do next. If you understand the load mix, you know where to focus your monitoring. A residential evening peak is a very different analysis window than a commercial midday plateau.
A voltage complaint on a feeder full of similar customers points towards coincident peaking, while elevated THD on a low diversity circuit suggests harmonic stacking. And when it comes time to recommend corrective action, understanding diversity helps you distinguish between the system is undersized or the load mix has shifted. Two problems that lead to very different solutions.
Recognizing these patterns transforms raw monitoring data from a wall of numbers into a coherent story.
Bringing It All Together
Load diversity is a measurable characteristic of every electrical circuit. It influences whether voltage stays within limits, whether harmonic distortion remains manageable, and whether power is clean enough to keep equipment running. Knowing how to recognize shifts in diversity is what turns a power quality investigation from guesswork into diagnosis.
Load Diversity Within a Single Building
Another aspect where load diversity is applied is inside a single building or facility. Within a building, there’s load diversity in miniature from what Scott was talking about, where the individual loads in a building are switching off and on at different times. And situations where that’s not the case can also lead to unexpected power quality issues.
For example, a car wash is a common scenario where I’ve seen a lot of PQ issues, where the transformer’s sized for the motors that are in there, but not all starting simultaneously. And some practices in the car wash, especially when the car comes from the dryer, a lot of blower motors that start simultaneously, which causes sags and power quality issues. And there, just staggering the start to those motors by even a fraction of a second or a second can provide enough diversity so that you don’t have loads happening at the same time.
Or obviously in a poultry plant, for example, where there’s a continuous process where there’s dozens of small motors that all start and stop simultaneously, which effectively looks like one giant load. And the transformer size assumes some sort of load diversity in the building. But in that situation, the majority of loads were all synchronized together, so there was no diversity whatsoever, and it was one giant load.
So you can have load diversity. It’s normally thought of within an entire circuit like Scott was talking about, but it scales down even within a building. So any time you don’t have that load diversity, then you have an assumption that’s not really true anymore, and that can lead to power quality issues. The system is designed with that assumption in mind, so it’s not overbuilt.
Wrap-Up
Thank you, Chris. Those are some very good insights. I think we can wrap up here, but if you have any questions, feel free to reach out to our tech support. Be sure to check out all the additional links for more information. And as always, thanks to everyone for tuning in, and have a great rest of your day.
