Electromagnetic relay testing is the laboratory process of verifying whether an electromechanical elementary relay meets the safety, functional, and reliability requirements set out in IEC 61810-1 / GB/T 21711.1-2023. The test scope spans four families of measurement defined in IEC 61810-7: coil electrical characteristics, contact performance at a standardized 6 V / 10 mA test condition, operate and release values, and insulation/dielectric withstand between coil and contacts.
What Does Electromagnetic Relay Testing Measure?
An electromagnetic relay is an all-or-nothing electromechanical switch: a low-voltage coil generates a magnetic field that pulls an armature, changing the state of a set of contacts (normally open / normally closed). Because the coil and the switched load circuit are galvanically separated, the failure modes split along the same boundary. Testing therefore measures two physically distinct subsystems against the same standard.
| Subsystem | What the test measures | Typical failure mode detected |
|---|---|---|
| Coil | DC resistance, pick-up (operate) voltage, drop-out (release) voltage, insulation resistance coil-to-frame | Open winding, inter-turn short, coil aging |
| Contacts | Contact resistance at 6 V/10 mA, bounce time, weld status (NO/NC state) | Arc erosion, pitting, contamination, contact adhesion |
| Coil ↔ contact isolation | Dielectric withstand voltage, impulse voltage, creepage/clearance | Insulation breakdown, tracking |
| Mechanism | Electrical endurance (cycles to failure), B10 reliability | Spring fatigue, mechanical wear |
A relay that "clicks" on the bench can still have pitted contacts with resistance high enough to fail under rated load — which is exactly why the SERP-dominant beep-test is treated here only as a field-screening step, not as a laboratory result.
Which Standard Governs Electromagnetic Relay Testing?
The governing document family is IEC 61810, adopted in China as GB/T 21711. Beijing ZKGX Research anchors every relay test report to these parts:
- IEC 61810-1:2015 / GB/T 21711.1-2023 — General and safety requirements for electromechanical elementary relays in low-voltage equipment (max 1000 V AC / 1500 V DC). Defines insulation coordination, impulse withstand, temperature rise, creepage and clearance.
- IEC 61810-7 — Test and Measurement Procedures (86 pages). The procedural backbone: how coil resistance, contact resistance, operate/release values, timing, and dielectric tests are actually performed and reported.
- IEC 61810-2 / 61810-2-1:2017 — Reliability; defines the B10 value (number of operating cycles at which 10% of a relay batch has failed) and severity levels (commonly level B).
- IEC 61810-3 — Relays with forced contacts, for safety-related circuits (harmonized as EN 50205).
A frequent source of confusion on the SERP is that "relay testing" is used interchangeably for two unrelated objects. IEC 61810 covers elementary (component-level) relays; protective relays for power-system protection (overcurrent, distance, differential) are tested under a different framework using IEC 60255 with secondary-injection test sets. This article addresses only the elementary component relay.
How Is Coil Resistance Tested and What Is the Acceptance Range?
Coil resistance is the first measurement in any relay test plan because it screens for open and shorted windings before any energized test is attempted. The procedure per IEC 61810-7 is a four-wire (Kelvin) DC resistance measurement at a defined reference ambient, typically 20 °C or 25 °C, with the coil de-energized and at thermal equilibrium.
The acceptance criterion is not a universal number — it is the manufacturer-declared nominal resistance ± tolerance, read from the datasheet. Typical bands:
| Coil nominal voltage | Typical DC resistance | Failure signal |
|---|---|---|
| 5 V DC (PCB / signal relay) | 40–90 Ω | OL → open winding |
| 12 V DC (automotive) | 50–120 Ω | ≈0 Ω → inter-turn short |
| 24 V DC (industrial) | 280–1100 Ω | Drift > tolerance → coil aging |
A bench multimeter in two-wire mode is acceptable only for screening; for a test report the resistance must be corrected to the reference temperature using the copper temperature coefficient (0.00393/°C at 20 °C), because a coil 15 °C above ambient reads roughly 6% high and can be misjudged as out of tolerance. The output of this test is a single value (in ohms) with its measured ambient, compared against datasheet nominal.
What Is the Standard Contact Resistance Test Condition?
This is the single biggest gap between hobbyist content and laboratory practice. The SERP commonly tells readers to "set continuity mode and listen for a beep." IEC 61810-7 does not accept a beep as data. The standard test condition for contact resistance of an elementary relay is defined at a fixed load — conventionally 6 V open-circuit voltage and 10 mA test current (the CC2 category) — measured with a four-wire micro-ohmmeter or a dedicated relay test set.
Why the fixed condition matters: at higher test currents the contact film punctures and reads artificially low; at lower currents a contaminated contact reads artificially high. The 6 V / 10 mA window exposes the true condition of the contact surface. Acceptance is against the datasheet maximum (commonly ≤ 50 mΩ for a new signal relay, ≤ 100 mΩ for a power relay), measured on the closed contact both in the de-energized NC state and in the energized NO state.
A contact that passes a beep test but reads 300 mΩ under the 6 V / 10 mA condition has a contamination or pitting defect that will overheat under rated load — the precise failure the beep-test misses.
How Are Operate (Pick-Up) and Release (Drop-Out) Voltages Measured?
Operate and release values verify that the relay actuates within its declared window. The IEC 61810-7 procedure ramps the coil voltage from zero while monitoring contact state:
- Pick-up (operate) voltage — ramp up slowly from 0 V; record the voltage at which the NO contact first closes. Must be ≤ 70–80% of nominal (per datasheet), so the relay pulls in reliably even with supply sag.
- Drop-out (release) voltage — from nominal, ramp down; record the voltage at which the contact returns to the de-energized state. Must be ≥ 10% of nominal; below this the relay may fail to release under residual voltage or EMI.
The compliance window between pick-up and drop-out is the relay's hysteresis band. A relay whose release voltage has collapsed to near zero (a sign of residual magnetism or worn return spring) will not drop out when commanded and is failed. Both values are reported as a percentage of nominal coil voltage alongside the absolute measured volts.
What Is the Difference Between a Functional Test and an Endurance Test?
Functional testing verifies a single actuation; endurance testing verifies the relay across its declared electrical life. These answer different questions and are not interchangeable.
Functional / timing test — a single energize-de-energize cycle measured for operate time, release time, and contact bounce time (typically tens of microseconds of bounce). Pass criterion: timing within datasheet limits and clean contact transition with no bounce-induced miscount.
Electrical endurance test — repeated making and breaking of a defined load (resistive, inductive, or lamp, at rated current) for a defined number of cycles. Per IEC 61810-2, electrical life is expressed as cycles to failure (CTF), with severity commonly cited as level B:
- Mechanical endurance (no load): typically ≥ 10⁶ (1,000,000) operations
- Electrical endurance at rated load: typically on the order of 5 × 10⁴ (50,000) cycles
- B10 value: the cycle count at which 10% of a sample batch has failed, verified per IEC 61810-2-1:2017
A relay can pass every functional test on day one and still fail its endurance target because the dominant failure mode — cumulative arc erosion of the contact material — only appears after tens of thousands of cycles. For any application where the relay is a safety or duty-cycle-critical component (smart switches, industrial control, automotive), endurance testing is the test that actually validates reliability.
How Is Insulation and Dielectric Withstand Tested?
Because the coil circuit and the load circuit are galvanically isolated, the dielectric test verifies that isolation holds under overvoltage. IEC 61810-1 / GB/T 21711.1 defines the test between all current-carrying terminals tied together and the frame, and between the coil and the contacts:
- Insulation resistance — measured with a 500 V DC megger; typical acceptance ≥ 100 MΩ.
- Dielectric withstand — a power-frequency voltage (commonly 1 kV or 2.5 kV RMS depending on rated insulation voltage) applied for 1 minute; no breakdown or flashover permitted.
- Impulse withstand voltage — a 1.2/50 μs standard lightning impulse at the declared impulse level (e.g., 4 kV or 6 kV peak), verifying coordination with the overvoltage category of the installation.
These three are the safety gate of the standard. A relay that switches correctly but fails dielectric withstand is unsafe to install because a single transient will bridge the coil-to-contact barrier.
Our Testing Capabilities
Beijing ZKGX Research conducts electromagnetic relay testing as an ISO/IEC 17025 testing laboratory. The relay test scope we cover, mapped to the standards above:
- Standards basis: IEC 61810-1 / GB/T 21711.1-2023 (general & safety), IEC 61810-7 (test procedures), IEC 61810-2 / 2-1 (reliability, B10).
- Measurement items: coil resistance (4-wire, temperature-corrected), contact resistance at the 6 V / 10 mA CC2 condition, operate/release voltage and timing, contact bounce, dielectric withstand, impulse withstand, insulation resistance.
- Endurance testing: electrical endurance cycling at rated load with cycles-to-failure reporting and B10 verification per IEC 61810-2-1.
- Sample types: PCB / signal relays (5 V, 12 V, 24 V coils), automotive 12 V/24 V relays, industrial power relays, safety relays with forced contacts (IEC 61810-3).
- Deliverable: a test report stating measured value, applied condition, and pass/fail against the declared datasheet limit for each item.
If you have a relay sample or a datasheet requiring verification, contact our testing team to scope the test items and turnaround.
Frequently Asked Questions
Can a relay pass a multimeter beep test and still be defective?
Yes. A beep only confirms that current can flow through the contact at near-zero load. The same contact can read 300 mΩ under the IEC 61810-7 6 V / 10 mA condition, indicating pitting or contamination that will fail under rated current. Continuity is a field screen, not a laboratory result.
What voltage should an electromagnetic relay pull in at?
The pick-up voltage must be ≤ 70–80% of the nominal coil voltage (per the datasheet), measured by ramping up from zero and recording the value at which the NO contact closes. This margin guarantees reliable actuation even with supply voltage sag.
What is the B10 value in relay testing?
The B10 value, defined in IEC 61810-2, is the number of operating cycles at which 10% of a relay sample batch is expected to have failed. It is the statistical reliability metric, verified by endurance cycling per IEC 61810-2-1:2017 — distinct from the functional pass/fail of a single actuation.
Is electromagnetic relay testing the same as protective relay testing?
No. Electromechanical elementary relays (the component on a PCB or in an appliance) are tested under IEC 61810. Protective relays used in power-system protection (overcurrent, distance, differential) are tested under IEC 60255 with secondary-injection test sets and TCC curve verification — a different object and a different standard family.
Which Chinese standard corresponds to IEC 61810?
GB/T 21711.1-2023 (基础机电继电器 第1部分：总则与安全要求) is identical to IEC 61810-1:2015, effective 2023-10-01, replacing GB/T 21711.1-2008. CQC certification of relays in China now requires the 2023 edition.