Robot Dielectric Strength Testing: Standards, Methods, and Compliance Requirements

Robot dielectric strength testing is a mandatory electrical safety verification that confirms a robot's insulation system can withstand specified overvoltages without breakdown, protecting operators from electric shock and preventing catastrophic equipment failure. This technical article explains the applicable international standards, typical test samples, testing procedures, voltage requirements, and practical considerations for industrial robots, collaborative robots, mobile robots, and service robots evaluated by accredited third-party laboratories.

Technical Overview

The dielectric strength test, also known as the withstand voltage test or hipot (high potential) test, is one of the most fundamental electrical safety tests applied to robotic systems. Its purpose is to verify that the insulation between live parts and accessible conductive parts, and between circuits operating at different voltage levels, can withstand momentary overvoltages—such as switching transients, surges, and faults—without breakdown, flashover, or tracking. Because robots combine power electronics, servo drives, motors, long cable harnesses, and operator-accessible surfaces such as teach pendants and enclosures, the dielectric strength test is a critical gate for demonstrating compliance with machinery safety and product safety standards.

For industrial robots, the primary normative references are ISO 10218-1 (safety requirements for industrial robots), which points to IEC 60204-1 and its Chinese adoption GB/T 5226.1 for the electrical safety of machine equipment. Household service robots are typically evaluated against the IEC 60335-1 / GB 4706.1 series, while medical and surgical robots fall under IEC 60601-1 and related particular standards such as IEC 80601-2-77. During the test, a voltage significantly higher than the rated working voltage is applied between defined insulation barriers for a specified duration, and the leakage current and breakdown behavior are monitored. The specimen passes if no breakdown occurs and the measured leakage current remains below the limit specified by the applicable standard.

According to IEC 60204-1, typical test voltages include 500 V for SELV and PELV circuits, 1500 V AC for working voltages up to 300 V, 2000 V AC for working voltages above 300 V up to 690 V, and 1000 V plus twice the working voltage for circuits above 690 V. An alternative impulse dielectric test using 1.2/50 µs impulses (for example, 2500 V peak for circuits up to 300 V, applied with three positive and three negative impulses) may also be used. Always verify the exact values against the current edition of the applicable standard, as limits are periodically revised.

Testing Samples

Industrial Robot Manipulators

Six-axis articulated arms, SCARA robots, delta (parallel) robots, and Cartesian/gantry robots are tested to verify the insulation integrity of servo motor windings, internal wiring, slip-ring or connector assemblies, and the dielectric separation between power conductors and the mechanically grounded robot structure.

Robot Controllers and Drive Cabinets

Robot controllers containing servo drive modules, power supplies, braking units, safety relays, and input/output interfaces are tested between the supply terminals (phase and neutral conductors shorted together) and the protective bonding circuit, as well as between independent circuits such as mains, control, and fieldbus sections.

Teach Pendants and Operator Interfaces

Hand-held teach pendants, HMIs, and enabling devices are considered accessible parts and are therefore subjected to stricter requirements, often at reinforced insulation levels, because they are gripped directly by operators during programming and manual operation.

Collaborative Robots

Cobots evaluated under ISO/TS 15066 and the ISO 10218 series undergo dielectric testing with particular attention to power-limited drive circuits, torque sensors, force-torque sensor cabling, and the skin-like surfaces that make contact with human operators.

Mobile Robots (AGV/AMR)

Automated guided vehicles and autonomous mobile robots are tested across their integrated battery systems, charging interfaces, motor controllers, and safety laser scanner circuits, including the insulation between the battery bus and the conductive chassis.

Service and Household Robots

Robotic vacuum cleaners, floor scrubbers, and robotic lawn mowers are tested per the appliance safety framework, with test voltages differentiated by insulation class—for example, basic insulation and reinforced insulation are verified at different voltage levels, and the reinforced insulation test for a 230 V appliance is typically 3000 V AC for one minute.

Robot Subassemblies and Components

Servo motors, encoders, harmonic and RV reducers with integrated sensors, brake units, cable sets, connectors, and end-effector components are individually tested during design verification and incoming inspection to ensure insulation defects are caught before assembly.

Testing Items

A complete dielectric strength evaluation program for robots generally includes the following items, selected according to the applicable standard and the product category:

• AC power-frequency dielectric withstand test between supply conductors and the protective bonding circuit (chassis/earth).
• AC dielectric withstand test between mutually independent circuits (for example, mains to SELV control circuits).
• Dielectric withstand test of SELV/PELV circuits, typically at 500 V.
• Reinforced insulation withstand test for operator-accessible parts such as teach pendant housings and connectors.
• DC dielectric withstand test as an alternative where circuit capacitance would produce excessive AC charging current, with the DC test voltage set at the AC value multiplied by the square root of two.
• Impulse dielectric withstand test using 1.2/50 µs impulses as an alternative permitted by IEC 60204-1.
• Insulation resistance measurement at 500 V DC, requiring a minimum of 1 MΩ, performed prior to the dielectric test as a precondition check.
• Humidity preconditioning (damp heat treatment) followed by dielectric testing to evaluate insulation performance under moist environmental conditions.
• Routine production-line hipot test, commonly permitted as a one-second test at an elevated voltage (for example, 120% of the type-test voltage under IEC 60204-1) for 100% of manufactured units.

Testing Methods

The dielectric strength test is performed with a calibrated high-potential tester capable of delivering an essentially sinusoidal 50 Hz or 60 Hz output (or a regulated DC output), with accurate voltage indication, leakage current measurement resolution of at least 0.1 mA, adjustable trip thresholds, and arc-breakdown detection. Test stations must be equipped with safety interlocks, guarding, and proper grounding to protect laboratory personnel from the hazardous voltages involved.

The general procedure is as follows: first, the robot is de-energized and disconnected from any external power source. Components that cannot withstand the test voltage—such as surge protective devices, certain filters, or electronic assemblies—are disconnected where the applicable standard permits. All line conductors (L and N) are shorted together, and accessible conductive parts are connected to the protective bonding terminal. The test voltage is applied between these two groups, starting from a low value (commonly below half of the full test voltage) and raised smoothly to the specified level over several seconds to avoid switching transients. The full voltage is then maintained for one minute for type testing, or for one second at an elevated voltage for routine production testing. After the test, the output voltage is reduced gradually and the specimen is discharged before disconnection.

The specimen is judged to have passed if no disruptive discharge (breakdown or flashover) occurs and the leakage current does not exceed the limit defined by the standard. Testing is normally conducted under standard laboratory atmospheric conditions, such as an ambient temperature of 15 °C to 35 °C and relative humidity not exceeding 75%, unless humidity preconditioning is specifically required. When a dielectric test must be repeated on the same specimen, many standards require a reduced voltage (for example, 80% of the original test voltage) to avoid cumulative insulation stress. Test reports issued by accredited third-party laboratories document the test points, applied voltages, duration, leakage currents, and observed results, forming an essential part of the safety evidence file for certification and market access.

Applications

Dielectric strength testing of robots serves multiple purposes across the product lifecycle:

• Design verification during R&D, where insulation coordination, creepage and clearance distances, and material selection are validated before mass production.
• Type testing and conformity assessment for CE marking under the machinery legislation of the European Union, using harmonized standards such as EN 60204-1 and EN ISO 10218-1 as the technical basis.
• Certification testing for North American and other international market access, where national deviations of IEC-based or UL-based standards may specify alternative test voltages and leakage limits.
• Compliance demonstration for medical robots under IEC 60601-1, where means of operator protection (MOPP) impose substantially higher test voltages, for example 4000 V AC for two means of protection.
• 100% routine safety screening on production lines to detect workmanship defects such as pinched wires, damaged enamel on motor windings, and incomplete potting.
• Post-repair and retrofit verification after motor replacement, harness rework, or controller refurbishment, and periodic requalification of robots that have been in long-term service in harsh environments.
• Failure analysis support, where dielectric test results combined with insulation resistance and partial discharge data help localize insulation degradation caused by thermal aging, moisture ingress, contamination, or voltage stress from fast-switching drives.

FAQ

What is the difference between a dielectric strength test and an insulation resistance test?

The insulation resistance test applies a low-power DC voltage (typically 500 V) and measures resistance in megohms to assess the general condition of insulation, whereas the dielectric strength test applies a much higher AC or DC voltage to prove that the insulation can withstand overvoltage stress without breaking down. In IEC 60204-1 evaluations, the insulation resistance measurement (minimum 1 MΩ) is normally performed first, and the withstand voltage test follows.

Why is humidity preconditioning required before the dielectric test?

Robots often operate in humid industrial environments where moisture can condense on insulating surfaces and reduce dielectric performance. Damp heat conditioning before the test reveals weaknesses such as hygroscopic materials, insufficient encapsulation, and inadequate creepage distances that would not appear under dry laboratory conditions.

Can the dielectric strength test damage the robot's electronics?

The test is designed to stress insulation barriers, not functional circuits. Sensitive electronic modules, surge protective devices, and components rated below the test voltage are disconnected in accordance with the allowances in the applicable standard. When executed by experienced accredited third-party laboratories using correct ramping and discharge procedures, the test does not degrade properly designed insulation.

When should a DC hipot test be used instead of an AC test?

DC testing is preferred for circuits with significant capacitance—such as long servo cable runs, EMI filters, and motor windings—where AC testing would produce large capacitive charging current that obscures real leakage current readings. The DC test voltage is set at the AC requirement multiplied by the square root of two to achieve equivalent stress.

What are the most common causes of dielectric test failures in robots?

Typical root causes include insufficient creepage and clearance distances, insulation damage from cable flexing in moving joints, moisture or coolant contamination inside connectors and junction boxes, thermal aging of motor winding insulation, and voltage stress imposed on motor insulation by the steep voltage edges (high dv/dt) of modern servo drives.

How often should dielectric strength testing be repeated?

A full-voltage type test is performed during certification of a new robot model, and routine one-second tests are applied to every manufactured unit. After major repairs, motor or harness replacement, or retrofit of a controller, a verification test—often at a reduced voltage such as 80%—is recommended to confirm that insulation integrity has been restored before the robot returns to service.