By Jason Axelson, Fluke Subject Matter Expert, Power Quality
Data centers depend on clean, reliable power to maintain the uptime their client’s demand. But not all power problems are obvious. Harmonics can silently interfere with equipment, reduce efficiency, and even lead to costly downtime. Because power issues cause roughly 40 percent of unplanned outages, monitoring for harmonics is a crucial step in maintaining system health and client trust. With the right tools and setup, data center operators can detect and correct harmonics before they cause damage.
Why Monitor Harmonics in a Data Center?
Harmonics can cause excessive heat, equipment damage, and unplanned downtime. The symptoms of harmonics often go unseen, and the results can be invisible until the damage is already done.
Data centers serve as storage and maintenance hubs for customer data, and in some cases, customers supply their own server racks. In these environments, monitoring harmonic distortion helps data center operators validate how added equipment affects the overall power quality and ensures one client’s equipment doesn’t negatively impact others. If equipment is damaged and harmonics are suspected, having a record of ongoing quality monitoring also helps demonstrate due diligence and reduce liability.
Monitoring harmonics in data centers gives early warnings and shows trends, giving data centers the opportunity to take steps to mitigate the harmonics before critical failures occur. In this article we’ll explore how to monitor harmonics in a data center and discuss best practices and tools to simplify the process.
Where to Measure Harmonics in a Power System
There are several key areas where harmonics can hide in data centers.
- Point of Common Coupling: The point of common coupling (PCC), where the facility connects to the grid, can be a source of harmonics coming into the facility. The Institute of Electrical and Electronics Engineers (IEEE) has created standards for harmonics limits at the PCC, and monitoring this is key to ensuring the power quality meets these standards.
- Uninterruptible Power Supplies (UPS): UPS systems are designed with some adjustability due to adverse power conditions such as high harmonic content. UPSs will typically switch to battery power under these circumstances, which can compromise battery life expectancy and ride through.
- Computer Room Air Conditioners (CRACs) and Air Handlers (CRAHs): Motors and fans operating these units use variable speed drives. While these can help conserve energy because of their ability to run at different speeds, they can also inject harmonics into the system.
- Lighting/IT loads: Harmonic frequencies can cause LED drivers inside the lighting circuit to fail, leading to flickering lighting or even fully failed lights. Even if the flickering is too fast for human eyes to register, it can still cause headaches for employees working in areas where harmonics are present.
When measuring for harmonics, make sure to check both phase and neutral conductors. Most power analyzers are capable of monitoring both. Phase monitoring reveals which loads are generating distortion, while neutral monitoring shows how those harmonics interact and accumulate.
Choose the Right Tool
Data center harmonic monitoring is typically performed with a power quality analyzer, such as the Fluke 1777 Power Quality Analyzer, or a power logger, such as the Fluke 1738 Three-Phase Power Logger. Both the Fluke 1777 and the Fluke 1738 provide quality type measurements.
Analyzers usually provide more advanced features required for event and harmonic evaluations but might lack memory storage for evaluations over long periods. Power quality analyzers are the right tool for providing instantaneous measurements or commissioning work for proof of work done. The 1777 captures fast voltage transients as well as providing more advanced measurements like harmonic power calculations providing assistance with harmonic direction such as source or load.
Power loggers are ideal tools for recording and analyzing power parameters, can display voltage and waveforms, and can measure and monitor harmonic distortion caused by electrical loads.
Fluke Step-by-Step Guide on Monitoring Power System Harmonics
Step 1. Verify System Voltage Configuration
Ensure the voltage setup matches the system you're measuring. Power quality tools measure RMS (Root Mean Square) voltage and current, which reflect the effective power being delivered to loads. Accurate RMS readings are essential for identifying distortion caused by harmonics and comparing measurements against equipment ratings.
Step 2. Select the Right Connection Type
When choosing a configuration with a neutral, Fluke tools automatically use phase-to-neutral voltage settings. This ensures correct vector calculation and harmonic detection. Note: If a neutral is available, Fluke recommends selecting a power configuration supporting measurement of the neutral conductor.
Step 3. Enter Potential Transformer Information (if applicable)
If your setup includes Potential Transformers (PT), manually enter the transformer ratio in the Fluke interface. Input the primary voltage to ensure proper scaling of measurements.
Step 4. Connect and Configure Current Probes
Most Fluke instruments feature auto-ranging current probes that are automatically detected when connected. For CTs (Current Transformers) used in medium to high voltage systems, check with the manufacturer to ensure it will support lower secondary current measurements. If so, manually enter the CT ratio to maintain accuracy.
Step 5. Check CAT Ratings and Accessory Safety
Fluke tools are CAT rated for maximum safety in industrial environments. Always verify that accessories (probes, leads, clamps) meet the required CAT rating for your application.
Step 6. Inspect Test Leads and Accessories
Before use, inspect test leads and connectors for signs of wear, cracks, or damage. Replace any compromised components to ensure measurement integrity and operator safety.
Always wear appropriate PPE (Personal Protective Equipment) when working on or near energized electrical systems. Consult Fluke safety sheets and product manuals for additional setup and safety guidance. These documents provide equipment-specific instructions and precautions.
Step 7. Log Total Harmonic Distortion (THD) and Specific Harmonic Orders
Fluke tools for power measurement use default setups that include harmonic measurements. Some tools offer the ability to incorporate more harmonics information or faster intervals for capturing harmonic data as well as different methods to calculate harmonics.
Reviewing the frequency spectrum of the signal can help you identify which harmonic orders are most dominant and whether they’re linked to specific types of loads, like VFDs or switching power supplies. Make sure you understand what configuration changes might need to be made or reach out to Fluke Technical Support for assistance.
Step 8. Choosing the Correct Logging Duration
For event-related issues, a typical logging duration is about one week for capturing relevant occurrences. In contrast, load studies often require logging for up to a month to ensure all possible load conditions are recorded, allowing for an accurate assessment of the panel’s maximum demand.
Step 9. Analyze the Data
Once the logging session is complete, it’s time to begin analyzing the data. Standards like G5 and IEEE 519 can help provide a baseline for interpreting Total Harmonic Distortion % (THD %), but these standards are utility quality standards and may not apply to harmonics caused by equipment within the data center. THD of up to 8 percent is recommended by IEEE 519.
Most power quality tools offer a live view feature that lets you see the current waveshape characteristics of the power system in real time. Capturing the waveform in a screenshot during this live view can be helpful for answering questions later. It's important to understand that these tools aren’t designed to store every waveform cycle over the course of their operation. Instead, they capture specific events based on industry standards or user-defined settings.
Waveform distortion is typically evaluated by reviewing the captured events. Keep in mind that not all tools provide detailed waveform data. Some may only generate a summary table showing event times, dates, and measurement values. If your analysis requires more in-depth waveform information, be sure to choose a tool capable of capturing that level of detail. When in doubt, consult a technical support specialist to ensure you’re using the right tool for your needs.
Common Mistakes and Best Practices
Monitoring harmonics can be a complex process, especially in complicated data centers with so much equipment and fluctuating demand that can impact the power quality and harmonics. Here are some common mistakes to avoid during monitoring:
- Underestimating logging duration: Monitoring for a few hours or even an entire day doesn’t give you a picture of the fluctuating load demands and resulting harmonics that can occur. At a minimum, logging should be done for a full week for a thorough analysis. In some cases, a longer logging duration may be ideal.
- Not capturing startup/shutdown behavior: When motor loads initiate, they draw a much higher current than they would during normal operation, so it’s important to capture these loads to get a complete picture of the conditions. Some tools support inrush capture, which can be useful for seeing additional load details.
- Forgetting to monitor neutral: Monitoring the neutral is important when checking for harmonics because harmonics can accumulate in the neutral conductor, leading to overheating, equipment damage, or even fire if left unchecked. Forgetting to connect to the neutral is a common mistake, but Fluke tools are built with a verification process to help you catch common errors like this. Note: Some configurations might not support the addition of the neutral, but if you have one, you should monitor it.
Monitoring harmonics effectively requires more than just plugging in an analyzer or logger. It requires careful setup, the right measurement points, and an understanding of how harmonics behave across phases and in the neutral.
Harmonics Monitoring Setup Checklist
Here are a few best practice tips to make sure your harmonics monitoring setup will help you collect the data you need.
- Use verification tools: Verification tools included in Fluke instruments are designed to ensure your instrument is set up and connected properly. Even the most knowledgeable technicians can make simple mistakes, and this tool is an easy way to double check that you’ll receive good data from monitoring.
- Check your display: Make sure the nominal voltage tracks to what the display shows live before beginning a recording.
- Check your recording mode: Make sure the mode of recording will include all the data you need.
- PT and CT ratios: Make sure PT and CT ratios are set up for medium and high voltage systems. Current clamps supplied with the tool may not support the necessary current resolution of a low current 5A secondary, and system current may exceed the applied clamp specifications. Make sure you have additional higher range clamps available if needed.
- Check power supply: Many Fluke devices can be powered directly from the circuit they’re measuring, so you don’t need to plug them into a separate power outlet or use an extension cord. This can make setup safer and more convenient, especially in industrial settings. However, it's important to check your specific device to confirm it supports this feature and to stay within its power input limits to avoid damage.
- Inrush current settings: Fluke tools offer additional settings to allow capture of inrush current. If you’re measuring this, make sure inrush triggers are enabled prior to beginning a recording.
- Date and time: Make sure the date and time of the tool are set correctly.
- Confirm data access: Most Fluke power analyzers and loggers let you download data even while they're still recording. However, you may need remote access to the device to do this. Before starting, make sure you have a reliable way to access the data. Confirm that any required software is installed and approved by IT or your facility. Test the connection by downloading a sample file. It doesn’t need to contain real data, just enough to confirm that the connection and download process are working correctly.
About the Author
Jason is a subject matter expert at Fluke specializing in power quality, electrical test equipment, and product applications. With deep experience supporting both customers and distribution partners, he helps professionals select, operate, and troubleshoot a wide range of diagnostic tools—including power quality analyzers, battery testers, acoustic imagers, and thermal imagers. Jason regularly leads application-based training sessions, drawing on his hands-on knowledge to bridge the gap between technical challenges and practical solutions across industries. Connect with Jason on LinkedIn.