If you’ve ever worked with high-voltage (HV) systems—think of the power grids that keep cities running, the medical equipment that saves lives, or the aerospace avionics that keep planes safe—you know that even the tiniest component failure can have massive, dangerous consequences. As the head of our company’s High-Voltage Chip-Type Glass-Glaze Resistor Dividers division, I spend a lot of time walking new engineers through why our resistors are a critical part of these systems, and one question comes up more than any other: “How do you prove these components can handle the high insulation demands they’re rated for?” That’s where insulation resistance testing comes in. It’s not just a checkbox for us—it’s a non-negotiable step in making sure every resistor leaves our facility ready to do its job, no matter the voltage or environment. Let me break down what this test actually entails, why it matters for our glass-glaze chip resistors specifically, and how we’ve refined our process over the years to deliver consistent, reliable results for our clients. High-Voltage Chip-Type Glass-Glaze Resistor Dividers
First, let’s get clear on what insulation resistance even means for a HV glass-glaze resistor divider. A chip-type resistor divider is made of two (or more) individual resistive elements printed onto a ceramic base, covered with a glass glaze coating for environmental protection, and terminated with metal end caps that connect to the circuit board. The divider’s job is to step down high input voltages to a lower, measurable output—for example, a 100kV input getting stepped down to 10V for monitoring. For this to work safely, there needs to be zero electrical current leaking between the resistive elements, between the resistors and the ceramic base, and between the terminals of different divider arms (if it’s a multi-ratio design). That leakage would throw off the voltage divider ratio, cause overheating, or even create an arc that shorts the entire system. Insulation resistance (IR) is the measure of how well a material (in this case, the glass glaze, ceramic substrate, or internal encapsulants) blocks that unwanted current.
Now, the test method itself isn’t just hooking up a multimeter and calling it good—there are strict standards and parameters we follow, tailored specifically to glass-glaze resistors. For our chip-type dividers, the most relevant standards come from the International Electrotechnical Commission (IEC) and the Institute of Electrical and Electronics Engineers (IEEE), specifically IEC 60115 (fixed resistors for use in electronic equipment) and IEEE 587 (insulation testing for high-voltage components). Let’s walk through our step-by-step process, the same one we’ve used for every order from our initial prototype runs to our largest volume clients.
First, pre-test preparation is non-negotiable. We don’t just pull resistors off the production line and test them—they have to be at a consistent temperature and humidity level, per standard conditions of 23°C ± 2°C and 50% relative humidity ±5%. Glass glaze is a hygroscopic material, meaning it absorbs moisture over time, and moisture is a killer for accurate IR readings. If a resistor is left out in a humid warehouse for a week, the glaze will hold enough water to skew results by orders of magnitude. So before any test, every lot is conditioned in our quality lab for 24 hours in a controlled environmental chamber to make sure all moisture levels are stable. We also inspect each resistor visually first—no chips in the ceramic base, no cracks in the glaze, no loose metal terminals. A tiny chip that’s not visible to the naked eye can create a direct leakage path, so we catch those before they even reach the test bench.
Next, we set up the test equipment. We use a high-voltage insulation resistance tester (often called a megohmmeter) rated for at least twice the maximum rated voltage of the resistor divider. For example, if we’re making a divider rated for 50kV, our megohmmeter is set to 100kV. Why? Because IR testing works by applying a fixed DC voltage across the insulation and measuring the amount of current that leaks through, then calculating resistance as R = V/I. If we use a voltage lower than the component’s rated operating voltage, we might not catch flaws that only show up under actual working conditions. A common mistake engineers make is using too low a test voltage, which gives a false sense of high insulation resistance—only for that resistance to drop drastically when the system is under full load. Our equipment also has a built-in function to measure “polarization index” (PI) and “dielectric absorption current” (DAR), two additional metrics that give us way more data than just a single IR reading. PI is the ratio of the IR reading at 10 minutes to the reading at 1 minute, and DAR is the ratio at 1 minute to 30 seconds. For glass-glaze resistors, we target a PI of ≥2 and DAR of ≥1.5—numbers that tell us the insulation material is stable, not just holding a temporary charge.
Once the equipment is calibrated and the resistors are prepped, we connect the test leads correctly, which is specific to our chip-type divider design. Unlike through-hole resistors, which have two leads, a divider has multiple terminals: the high-voltage input terminal, the low-voltage output terminal, and the ground terminal (for safety, many dividers have a dedicated ground connection to the chassis). So when testing, we apply the test voltage between the high terminal and the combined low + ground terminals. We also make sure to place the test probe’s guard electrode around the body of the resistor, right on the glass glaze surface. This is a critical step that most general resistor testers skip—guard electrodes eliminate “surface leakage” that would otherwise add to our measurement and give us an artificially low IR reading. Glass glaze is smooth, but even a tiny bit of residual flux from the soldering process or dust on the surface can create a thin conductive layer. The guard electrode pulls that surface current away from the measurement path, so what we’re left with is only the actual leakage through the bulk insulation material.
Now, the test sequence: we apply the test voltage slowly over 10 seconds, rather than jumping to full voltage immediately. Applying voltage too fast can cause dielectric absorption, where the insulation material holds a temporary charge that makes the initial IR reading look higher than it actually is. Once we hit full voltage, we take readings at 30 seconds, 1 minute, and 10 minutes, as required for PI and DAR. For our glass-glaze resistors, the minimum acceptable IR value is 10 GΩ per kV of rated voltage, tested at full rated operational voltage. That means a 50kV divider needs a minimum IR of 500 GΩ, and a 100kV divider needs 1 TΩ. That’s an extremely high bar, way higher than standard through-hole resistors, because our clients use these in systems where a leak even a milliohm too low can cause a failure.
Wait, let’s talk about why glass-glaze is such a good material for this, and why our test method is tailored to it. Glass glaze is a vitreous (glass-like) coating that’s fused to the ceramic substrate at over 500°C during manufacturing. It’s non-porous, chemically stable, and has extremely high intrinsic insulation resistance—far better than epoxy or polymer coatings, which are more common in lower-voltage resistors. But even the best glass glaze can have tiny micro-cracks or voids from the firing process, or contamination from manufacturing chemicals. Those flaws don’t show up under normal low-voltage testing, but under high stress during IR testing, they become paths for leakage. Our test method’s long hold time (10 minutes) also catches this: if there’s a micro-void in the glaze, the leakage current will slowly creep through that void, causing the IR reading to drop steadily over the 10 minutes. A good, flawless resistor will have a stable IR reading after the first minute, with only a tiny change over the 10 minutes. A flawed one will have a PI below 2, and we pull those units for rework or scrap.
We also run a “hipot test” (dielectric withstand test) alongside our IR testing, which is a separate step but often confused with it. Hipot applies an even higher voltage (usually 1.5 to 2 times the rated voltage) for a short period (1 minute) to test the component’s ability to withstand momentary overvoltage, like a power surge. But IR is a measure of static insulation resistance under operating voltage, so it’s a more reliable indicator of long-term reliability. We do both, of course—there’s no replacement for catching a unit that would break down under a surge—but IR is the test we use to validate a resistor’s long-term performance.
Over the years, we’ve refined our test process to handle the unique challenges of chip-type dividers, which are smaller and more compact than traditional HV resistors. A few years back, we had a client who was testing our 75kV dividers and getting inconsistent IR readings. We dug into their test setup and realized they were using a standard two-probe method, not adding the guard electrode. The small size of the chip meant surface leakage was accounting for almost 20% of their measurement. We adjusted our own test protocol to include guard electrodes on every test, and also started providing a data sheet with each lot that shows not just the 1-minute IR reading, but the PI and DAR, so our clients can replicate our results if they want to.
Another key part of our process is lot traceability. Every lot of resistors is assigned a unique ID, and we log all test data—temperature, humidity, test voltage, each individual reading—into our quality management system. If a client ever has an issue with a component, we can pull up the full test history for that lot, see exactly what the IR readings were, and trace it back to the production batch. That level of transparency is non-negotiable for HV components, where there’s no room for error.
Let’s also talk about real-world results. Last year, we supplied a set of 120kV divider assemblies to a company building a new industrial power transformer test system. Their old dividers from another supplier were failing IR tests after 6 months in the field, with insulation resistance dropping by 40% over that time. Our new dividers, tested using our standard IR method, had an average IR of 1.2 TΩ (well above our 1 TΩ minimum) and a PI of 2.8. After 12 months of continuous operation at full voltage, the client came back to us and reported that the IR of our dividers was still at 1.1 TΩ—almost no change. The difference? The glass glaze material we use, combined with our rigorous testing to catch even micro-flaws before the resistors leave our facility.
I know that for engineers who are new to HV resistor design, all this might sound like a lot of steps, but it’s what separates a component that just meets a minimum spec from one that’s safe and reliable for decades. The insulation resistance test for high-voltage glass-glaze chip-type resistor dividers isn’t a hoop to jump through—it’s how we protect our clients’ systems, their equipment, and even their workers. A lot of people in the industry will cut corners on testing, using lower voltages or shorter hold times to save time, but that’s a risk we’re not willing to take. Every component we build has to stand up to the same high standards we set in our test lab.
If you’re working on a project that requires high-voltage resistor dividers—whether it’s medical imaging equipment, aerospace systems, power grid monitoring, or industrial test gear—you know how critical reliable insulation is. We’ve spent years perfecting our insulation resistance test method for chip-type glass-glaze resistors, and we’re ready to help you design a system that’s safe, efficient, and built to last. Reach out to our team to discuss your specific requirements, and let’s make sure your high-voltage components are up to the task.
Y5U Series HV Disc Capacitor References
IEC 60115-1:2019, Fixed resistors for use in electronic equipment – Part 1: Generic specification
IEEE Std 587-2017, IEEE Standard for Insulation Testing of High-Voltage Components
Kao, C. C., Dielectric Phenomena in Solids, Academic Press, 2004
Anshan HVRTION Electronic Technology Co., Ltd.
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