Crest factor is an important parameter to pay attention to when choosing an appropriate UPS for your building. It shows whether a unit can handle your current peaks without distorting its output. Many people fail to properly match the crest factors of their connected loads with the capabilities of their uninterruptible power supply (UPS) systems simply because they’re too focused on wattage ratings.
In this blog post, we’ll walk you through the numbers used to calculate crest factors. If you need help choosing a UPS system that correctly fits your building, contact Nite and Day Power to speak with one of our professionals.
What Is Crest Factor?
Crest factor is the ratio of a signal’s peak current to its RMS current. Facilities take it into account when sizing a UPS. The following sections provide more detail on how it all works.
Peak Current Demand
Peak current demand describes the highest current a load draws at any instant. Common causes of these spikes include industrial machinery cycling on and nonlinear loads, such as computers and servers, that draw current in bursts as they convert AC power to DC.
RMS Current
The United States power grid runs at 60 Hz, which means it completes 60 AC cycles every second. If you froze the wave on an oscilloscope during one of those cycles to measure the current, the reading wouldn’t represent the whole wave since the current is constantly changing as the wave moves.
RMS current solves this issue by assigning a single number, measured in amps, that represents the steady current that would do the same amount of work as the oscillating wave.
Peak Divided by RMS
To find the crest factor, divide the peak amps by the RMS amps. For example, a load that peaks at 14 amps and draws 5 amps RMS has a crest factor of 2.8 (the result of 14 divided by 5). The crest factor doesn’t include a unit because amps divided by amps cancel out.
How Technicians Use Crest Factor To Size UPS Systems
An uninterruptible power supply has its own crest factor rating, expressed as a ratio, which describes the spikiest load it can supply without distorting its output; the typical value is 3:1. This helps you choose the most appropriate UPS system for your current setup.
When doing so, make sure the crest factor rating of your UPS meets or exceeds your load crest factor. If the rating falls short, the UPS may limit current, overload, shut down, or distort the voltage waveform.
The Wattage Rating Trap
When shopping for a UPS, many people make the mistake of only looking at the wattage. Even if your UPS delivers plenty of watts, it still clips peaks when its crest factor rating is below your load’s crest factor.
By matching the crest factors, your UPS handles both the steady power demands of your facility and any sharp current spikes.
Know Your Load Before You Buy
You can’t read the crest factor of your connected loads off a panel or a label. The numbers depend on the mix of machines you run and how their loads draw current together. Nite and Day Power performs power quality monitoring to capture how your facility draws current, including spikes that increase the crest factor.
When you schedule a full power analysis with Nite and Day Power, we do more than just check the wattage. We measure your minimum, typical, and maximum loads to size a UPS that meets your building’s demands.
Choose Professional Grade UPS Systems From Nite and Day Power
Matching the UPS crest factor rating to the crest factor of your connected loads delivers a clean output without clipping the peaks. If you need help measuring your load crest factor and choosing a UPS system that handles your daily operations, call Nite and Day Power at (800) 540-7693. We’ll perform a power analysis and recommend the right UPS for your building.
Crest factor isn’t the only rating you need to consider when sizing a UPS system, either. Check out our article on power factor ratings in UPS systems to understand how these can also affect your sizing decision.
