High voltage designs amplify every constraint, with the primary performance goal being reliability and safety. High voltage designs can fail spectacularly and they can present safety hazards to users of the product. Although safety considerations are a basic part of any high voltage design, grounding problems compound safety issues and can lead to product failure or compliance failure (or both).
To help ensure you don't create a compliance or safety risk, we identified some of the top grounding problems in high voltage layouts and some important tips to help keep your designs reliable. The problems outlined here span isolation boundaries, creepage violations, leakage paths, and chassis ground misuse. Each of these can independently cause a design to fail compliance testing or, worse, create a shock hazard in the field.
Ground in a high voltage system is not a single universal node. The definition of ground depends on the system topology, whether the power conversion is AC or DC, and where isolation boundaries exist. In AC systems, ground typically refers to the protective earth conductor, which is distinct from the neutral. In DC systems, ground usually refers to the return rail or common bus on one side of an isolation barrier.
The table below clarifies which connection serves as the ground reference in common HV system topologies:
| System Type | Ground Reference | Notes |
| AC-DC Converter (3-wire input) | Protective earth (PE) on AC side; DC common on secondary side | PE connects to chassis; secondary ground is isolated from PE unless bridged by Y-capacitors |
| DC-DC Converter (isolated) | Primary-side DC return; secondary-side DC return | These two grounds are galvanically isolated; connection between them is only through safety capacitors or optocouplers |
| DC-DC Converter (non-isolated) | Single DC return rail | Input and output share a common ground; no isolation boundary exists |
| Purely AC System (single-phase, 3-wire) | Protective earth conductor | Neutral is a current-carrying conductor and is not ground; PE provides fault protection |
| Purely AC System (single-phase, 2-wire) | No dedicated ground conductor | Chassis ground may still be referenced through a Y-capacitor to one AC line |
In every case, the designer must identify which node is the 0 V reference on each side of any isolation boundary and ensure that connections between those references are intentional, rated for the working voltage, and compliant with the relevant safety standard.
High voltage DC-DC converters accept an elevated input voltage and step it down to one or more target output voltages through a transformer-isolated topology. The isolation barrier between primary and secondary is the fundamental safety mechanism: it prevents hazardous voltage from appearing on the user-accessible output side. Safety capacitors (Y-rated capacitors) bridge this isolation barrier in a controlled manner, and their correct selection and placement is essential to both EMC performance and safety.
Safety capacitors in isolated DC-DC converters serve several specific functions:
In galvanically isolated designs, safety capacitors are used in two locations: at the input EMI filter (line-to-ground, or X and Y positions) and between the primary ground and secondary ground across the isolation barrier. These capacitors must be rated for the full working voltage plus a margin. For a 400 V DC bus, a Y1-rated capacitor with a voltage rating of at least 500 V DC (25% derating) is appropriate. Typical capacitance values range from 1 nF to 4.7 nF.
The voltage rating margin exists because, in a fault condition, the full input voltage can appear directly across the capacitor. If the capacitor fails short, the isolation barrier is breached and hazardous voltage reaches the secondary side.
A subtle but dangerous layout mistake occurs when a high voltage pin on one component directly faces a ground pin or ground connection on an adjacent component. IPC-2221 defines minimum creepage and clearance distances based on peak voltage, PCB layer, altitude, and coatings, and these limits must be enforced as PCB design rules. However, meeting the minimum distance alone does not eliminate the safety hazard when HV and ground features are oriented toward each other.
A direct short from an HV line to ground may occur through several mechanisms: a test probe slipping during bench testing and bridging the gap, conductive debris or a metal fragment landing on the PCB between the two exposed features, or a voltage surge that exceeds the dielectric withstand of the gap and causes arcing between the HV pin and the ground connection. In each case, the result is an uncontrolled fault current path that can damage the converter, blow upstream protection, or create a fire risk.
One solution is to apply margin (e.g., 50%) beyond the IPC-2221 minimum when HV pins and grounded features face each other. A better option is to reorient components so that ground pins face other ground pins and HV pins face other HV pins or face toward the board edge where no adjacent conductor exists. This eliminates the geometry that enables a short circuit from a single point failure. Where reorientation is not possible, a routed slot in the PCB between the HV pin and the ground feature provides additional protection by increasing the creepage path along the board surface.
Leakage current in high voltage systems is the small but measurable current that flows through unintended paths between energized conductors and ground or between primary and secondary sides of an isolation barrier. In some cases, the leakage flows from a ground connection that is exposed to a user. In HV designs, even microamp-level leakage becomes a concern because it can exceed the touch-current limits defined in safety standards such as IEC 62368-1 and IEC 60950-1 (legacy). EMC standards like CISPR 32 are also indirectly affected, as leakage paths that carry high-frequency noise contribute to conducted emissions.
| Location of Leakage | Cause |
| Across Y-capacitors (primary to secondary) | Intentional capacitance bridging the isolation barrier; value sets the leakage magnitude |
| PCB surface between HV traces and ground | Contamination, humidity, or insufficient creepage distance reducing surface insulation resistance |
| Through insulation of transformer or optocoupler | Aging, thermal cycling, or partial discharge degrading dielectric material |
| Between HV pins and mounting hardware | Flux residue, conformal coating voids, or condensation creating a resistive path to chassis |
| Input EMI filter capacitors to earth | Line-to-ground (Y) capacitors passing current at line frequency to the PE conductor |
IEC 62368-1 clause 5.7 specifies touch-current limits (typically 0.25 mA for handheld equipment, 3.5 mA for permanently connected equipment). IEC 61010-1 applies similar limits for measurement equipment. Designers must sum all leakage contributions and verify the total remains below the applicable limit under worst-case conditions, including maximum rated voltage and temperature.
Chassis and earth grounds serve purely protective roles, acting as a Faraday cage for shielding while providing a low-impedance safety path to dissipate noise, ESD, and fault currents without participating in the functional power path. In normal operation, these conductors are not intended for carrying current, but they may become current-carrying conductors during a fault or from unintended coupling.
This condition arises from one of three causes:
Current on the chassis from load-return, continuous faults, or AC coupling is a safety and compliance failure, risking shock, increasing leakage current (IEC 62368-1 failure), and causing conducted emissions (CISPR 32 failure).
The design rule is straightforward: the chassis and earth conductor must never be used as a power return path. Ground the DC return to the chassis at one point only, at the input where power enters the system, and verify that no layout or wiring decision creates a second connection that would allow load current to split between the intended return and the chassis.
To help identify potential radiated EMI sources in your HV PCB layout, look to DENPAFLUX for fast evaluation and qualification of your PCB design. We review your layout against the industry standards and regional regulations that apply to your product, then return a report that pinpoints likely EMI sources with concrete recommendations for fixing them.
How much we take on is your call. Some teams want an independent expert review to validate their direction. Others want us validating every step as they implement, with formal sign-off before each test. And some want EMC handled end to end so they can stay focused on the product. Whichever fits where you are, the same team and the same diagnostic depth sits behind your project.
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