Back To Basics: MIL-STD-810

Posted under Back to Basics, Educational, Technology on November 9th, 2025 by

I was recently discussing with a friend regarding a reliability testing project. We were discussing specifics on MIL-STD-810 and I wanted to discuss regarding that today.

MIL-STD-810 is the U.S. Department of Defence’s guide for engineering and validating hardware to survive real environments. It was launched in the 1960s, but the document has kept evolving. Its mainly about making your hardware survive dust, heat, rain, altitude, vibration etc and exposing weak designs. It is not just for defence products, if you build drones, outdoor electronics, field medical gear, or rugged laptops, you will meet these same parameters.

Inside the document there are three big parts. Part One explains how to build a life cycle environmental profile and how to sequence tests to simulate real life. Part Two is a bunch of laboratory methods with setups and procedures for temperature, humidity, rain, dust, fog, solar, icing, vibration, shock, and combined environments. Part Three provides climate data, so your test levels are realistic, instead of guessing.

Beyond that, it discusses how to choose test levels, set up the product, add simple sensors, and record results. You’ll see advice on test order, running tests together, packaging checks, mold exposure and work in areas with explosive gases.

Although I wouldn’t suggest reading the 1000+ page document end to end. I think it’s imperative that you know that something like this exists for free, and you can load it up in your favourite LLM and summarize for your particular use case. Because it teaches you to think like a reliability engineer. The standard does not hand you pass or fail numbers. If you need a start on how to build a quality rugged hardware, start here and fine tune it to your needs.

BTW, there is no “MIL-STD-810 certification”. The correct phrasing is tested in accordance with MIL Standard 810. Tell what you tested, why those levels were chosen, and what passed because MIL-STD-810 is not a certification standard.

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Back To Basics: Class X & Y Capacitors

Posted under Back to Basics, Educational, Tech Explained on November 2nd, 2025 by

I recently had to interact with a client specifically regarding Class X and Class Y capacitors, and I thought it will be a good refresher for the community as well.

These 2 caps are mostly used in the AC circuits. Class X sits across Line and Neutral and helps remove differential mode noise. Class Y connects from Line or Neutral to protective earth, or across the isolation barrier, to drain common mode noise safely. “X” and “Y” names are got from the international capacitor safety standard IEC 60384-14 for capacitors.

An across-the-line failure can cause fire, so X capacitors are built to be self-healing, pass surge and flammability tests. A line-to-earth failure could make exposed metal live and cause electric shock, so Y capacitors must fail open and are limited in capacitance to keep leakage current small.

There are subclasses. X parts are X1 and X2. X2 is the common choice for normal mains surges, X1 is for harsher industrial projects. Y parts are Y1 and Y2. Y2 goes from Line or Neutral to earth in Class I gear. Y1 is used when you bridge reinforced insulation across the isolation barrier. Pick only parts with safety marks like UL on the datasheet and body. Keep Y values small and check leakage current with I ≈ 2πfVC so the total stays within your power budget.

Think about tradeoffs. X caps can be larger and cut more differential noise, but they need discharge parts and space. A bleeder resistor is needed across the X capacitor to make sure you don’t get a shock after unplugging the AC. Typically, in 1-5MΩ range. Y caps keep users safe by failing open and by being small, but they add leakage, so values are limited.

Remember that many Y MLCCs lose capacitance with DC bias so leave margin or pick C0G or film. In humid regions, choose parts that pass 85C and 85% RH tests. Never replace safety capacitors with general purpose parts on the mains(I can’t stress this enough!).

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