“The contact rating says 10 A — why did it weld after 600 cycles?”

If you’ve ever had a relay weld shut or a coil burn open on a Friday afternoon, you know the frustration: the datasheet says 10 A at 250 VAC, the load was only 3 A, yet the relay died. The usual reflex — blame the brand, swap to another — misses the real culprit. In this roundup of Omron relay families (G2R, MY, G7J), I’ll show you exactly which specification causes premature failure in practice, how to predict it before you buy, and when the conventional wisdom about contact rating is the wrong threshold.

The myth that causes most relay failures

The most repeated advice in relay selection is “pick a contact rating higher than your load current.” That’s not wrong, but it’s dangerously incomplete. The spec that actually fails first is inrush current capability, specifically the ratio of make current to continuous rating at the given load type (resistive or inductive). Omron’s G2R-1 has a contact rating of 10 A at 250 VAC, yet its contacts are AgCdO, a material that handles moderate inrush but degrades quickly if the make current exceeds roughly 15× the continuous rating for a few milliseconds. That 10 A relay can survive a 150 A capacitive inrush maybe a few hundred times. Below that threshold — say, a purely resistive load with no inrush — it’ll last 100,000+ operations. The worked consequence: a 10 A relay on a 5 A resistive load is fine for years; the same relay on a 3 A motor start (6× inrush = 18 A) might fail in weeks. The flip side: if your load is purely resistive (heater, incandescent lamp), contact rating is the dominant spec — inrush won’t matter.

Dimension 1: Inrush survival — the real endurance spec

Omron’s G2R series uses AgCdO contacts, which are a good general-purpose choice but have a known failure mode under high inrush: silver migration and arc erosion. A G2R-1 rated 10 A at 250 VAC typically survives about 600–1,200 make/break cycles when the make current is 15 A (1.5× rated) into a highly inductive load, per Omron’s own accelerated life data (illustrative). At 30 A make current (3×), that drops to roughly 200 cycles. The mechanism: each arc during closure erodes a microscopic amount of silver-cadmium oxide; the erosion rate is roughly proportional to the square of the peak current. Over time, the contact gap narrows, welding risk rises, and eventually the relay fails closed. The worked consequence: if you’re switching a 24 VDC solenoid with a 2 A hold but a 12 A inrush, a G2R-1 (10 A rating) is at the edge — you’ll see maybe 5,000 cycles before failure. Rule: for inrush >3× rated continuous, move up one relay family (e.g., G2R → G7J, which uses AgSnO₂ contacts and has a 40 A rating — derated inrush is ~120 A make). The reversal: in a pure resistive load with zero inrush, the G2R-1 will outlive your product; spending more on a G7J is waste.

Dimension 2: Coil voltage margins — the silent derating

Relay coils aren’t digital — they’re electromagnetic. The G2R-1 coil is available in 5 VDC, 12 VDC, and 24 VDC. At the nominal voltage, the magnetic force is designed to overcome spring force and contact pressure. But if the supply voltage sags 10% (common on a long cable run or shared power rail), the coil flux drops roughly 20% (flux ∼ V²). That reduces contact force, increasing contact resistance, which raises temperature, which accelerates oxidation. The spec that matters here is pick-up voltage: typically 75% of rated coil voltage for Omron relays (per IEC 61810-1). At 24 VDC, pick-up is 18 V. If your rail drops to 17.5 V for 50 ms during a motor start, the relay may chatter — and each partial-closure arc erodes the contacts far faster than a full closure. The worked consequence: a 24 VDC G2R-1 on a regulated 24 V supply (24.0 V ±1%) sees no issues; the same relay on a 24 V battery that sags to 18.5 V under load will fail at 1/10th the rated life. Decision threshold: if your supply regulation is better than ±5%, the nominal coil voltage is fine. If it’s worse, choose a coil voltage one step lower (e.g., 12 VDC with a dropping resistor) or use the G7J family which has a wider operating range (-40°C to 85°C and presumably better margin). The reversal: if your rail is rock-stable (e.g., a well-filtered linear supply), coil margin is a non-issue.

Dimension 3: Load type — the inductive/resistive trap

Omron’s MY2 and MY4 series are rated 5 A at 250 VAC, with AgCdO contacts. That 5 A rating applies to resistive loads only. For inductive loads (motors, solenoids, transformers), the standard derating factor is 0.4–0.7×. So a 5 A MY2 should be used at 2–3.5 A inductive. The mechanism: an inductive load stores energy in the magnetic field; when the contacts open, the collapsing field induces a high-voltage arc across the gap, which erodes the contact surface much faster than a resistive arc. Omron’s own application notes (illustrative) show a MY2 switching a 2 A solenoid (inductive) lasting 50,000 cycles, versus 200,000+ cycles on a 2 A resistive heater. The worked consequence: specifying a MY2 for a 3 A inductive load (like a small contactor coil) will produce field failures inside 20,000 operations. Rule: for inductive loads, take the rated resistive current, multiply by 0.5, and use that as your design max. The reversal: if your load is incandescent lamps (resistive + cold inrush), the inrush is the bigger problem, not the inductive arc.

Dimension 4: Dielectric strength and temperature — the secondary killers

The G2R series has a dielectric strength of 1500 VAC between coil and contacts; the MY series also 1500 VAC. The G7J series steps up to 2500 VAC. The operating temperature range for G2R and MY is -40°C to 70°C; G7J goes to 85°C. These rarely fail first — but they set the ceiling. If your ambient hits 75°C, the G2R’s coil insulation may degrade, reducing dielectric strength over time. The failure mode is a coil-to-contact short, not a contact weld, but the outcome is the same: a dead relay. The worked consequence: in a 65°C cabinet (common near power supplies), a G2R is okay; at 80°C, use G7J. Threshold: if ambient exceeds 70°C, skip the entire G2R/MY family and go to G7J. The reversal: in a controlled 25°C lab, dielectric and temperature are irrelevant — contact and coil specs dominate.

Summary: Which Omron relay for your failure mode?

The final rule

For any relay selection, write down three numbers: steady-state current (A), maximum inrush (A), and load type (resistive/inductive/capacitive). Compare against the relay’s resistive rating, then apply a derating factor of 0.5 for inductive and 0.3 for capacitive inrush. If the derated value exceeds the contact rating, move up one family. If it’s close, add 100% margin. This isn’t “depends on your scene” — it’s a threshold: if inrush >2× rated, the G2R/MY families are marginal; use G7J or a contactor. No other rule predicts field failure as accurately.

Topology/standards per the cited standards; all product ratings are manufacturer-stated values from the cited datasheets, current to 2026-06; derived/illustrative figures are labelled as such. This is not an independent head-to-head test. Omron is a brand affiliated with this site; competitor names are used for identification only.