Which Omron Relay Stays Closed Under Your Real Load? A Failure-Mode Roundup

You’ve heard the popular claim: “A 10 A relay is a 10 A relay, and if your load is under 10 A you’re fine.” In controlled lab conditions that’s true. On a machine tool panel, a pump skid, or an HVAC controller with a real inrush load, that same relay can weld its contacts inside 500 cycles. The datasheet doesn’t lie, but it doesn’t tell you which parameter actually bites first. This isn’t a “best in show” — it’s a failure‑mode roundup. We’re going to walk through four constraints that kill relays under real load, and map them to the Omron relay G2R, MY, and G7J families so you can pick the one that stays closed when it counts.

1. Inrush Current vs. Contact-Rating — The “10 A” Trap

The G2R-1 and G2R-2 are both rated 10 A at 250 V AC. That’s a steady-state resistive rating. A motor start, a capacitor bank, or a solenoid valve can pull 6–10× its steady current for 8–12 cycles. If your steady load is 8 A but the inrush is 50 A peak, the G2R’s silver‑cadmium oxide (AgCdO) contacts will start to erode on the first few cycles. After maybe 1,000 operations the contact gap increases, the arc extinguishing worsens, and you get a welded contact or a failure to open. Mechanism: AgCdO has good arc‑quenching properties but limited resistance to high‑peak erosion compared to silver‑tin oxide (AgSnO₂). The G7J-4A, rated 40 A at 250 V AC and equipped with AgSnO₂ contacts, will survive the same inrush for orders of magnitude more cycles. Worked consequence: If you have a 1.5 HP motor (approx 8 A steady, 48 A inrush) and cycle it daily, a G2R-1 will fail in under a year; the G7J-4A will outlast the machine. When this flips: If your load is purely resistive (heater, incandescent lamp) and never exceeds the 10 A steady rating, the G2R is cost‑effective and its failure-mode shifts to mechanical wear, not electrical erosion. For a heater that cycles 4×/day, the G2R-2 with socket mounting is easier to replace than a panel‑mount G7J.

2. Coil Voltage Drop — The “Holding” Threshold

All Omron relays in this roundup use DC coils (5, 12, or 24 VDC). The G2R and MY series specify a pickup voltage of 70–80% of rated coil voltage, but the dropout (release) voltage is typically 10–15%. That wide dropout hysteresis is intentional: once the relay picks up, it stays closed even if the coil voltage sags. But in a real control panel with long wire runs, voltage drop under load can pull the coil voltage below the dropout threshold. Mechanism: For a 24 VDC G2R-2 with a 144 Ω coil (approx 167 mA), a 100‑foot 18 AWG run adds about 0.64 Ω. At 0.167 A, the drop is only ~0.11 V — negligible. But if the same wire also feeds an adjacent solenoid that draws 2 A, the shared return sees a drop of 1.28 V, bringing coil voltage to ~22.7 V. If the control supply is minimally regulated and sags to 21.5 V under load, the relay drops out. Worked consequence: The MY2 with its higher coil power (approx 0.9 W vs the G2R’s ~0.4 W at same voltage) is slightly less sensitive to drop because its magnetic circuit has more ampere‑turns margin. But the G7J-4A, with a coil power of about 1.8 W at 24 VDC, is the most tolerant. When this flips: If your control supply is a dedicated, regulated 24 VDC bus with short (

3. Dielectric Withstand — The Arc‑Over Limit

Both the G2R and MY series list dielectric strength of 1,500 V AC. The G7J series is rated 2,500 V AC. That’s the voltage the insulation between coil and contacts can survive for 1 minute without breakdown. In a relay that’s switching an inductive load, the flyback voltage can spike to 500–1,000 V within microseconds. If the dielectric margin is too thin, internal arcing can carbonize the insulation over time. Mechanism: The G2R’s 1,500 V rating is tested at 50/60 Hz. A fast inductive spike (dV/dt > 1 V/μs) can break down a small air gap even at lower peak voltage. The G7J’s 2,500 V rating provides a wider safety margin for high‑inductive switching (contactors, transformer primaries). Worked consequence: Switching a 2 kVA transformer primary (approx 8 A at 250 V AC) with a G2R-1: the inrush is moderate, but the turn‑off voltage spike can exceed 1,000 V. Over 10,000 cycles, the insulation may degrade. The G7J-4A will handle the same duty with negligible risk. When this flips: For resistive or lightly inductive loads (solenoid valves with snubbers), the G2R’s 1,500 V is more than sufficient. The extra cost and panel space of the G7J are wasted.

4. Operating Temperature — The Ambient Ceiling

The G2R and MY series operate from –40°C to 70°C; the G7J from –40°C to 85°C. The 15°C difference is often dismissed as a “nice to have.” In a sealed panel near a motor, or in direct sunlight in a desert installation, ambient can hit 65°C. At 70°C, the G2R’s coil temperature rise (self‑heating plus ambient) can top 100°C, exceeding the insulation class (typically Class B, 130°C). Mechanism: Coil resistance increases with temperature (copper has ~0.39%/°C tempco). At 70°C ambient, a 24 VDC coil with a 144 Ω cold resistance at 20°C becomes ~172 Ω hot. Pickup current is fixed by the magnetic circuit, so the coil voltage needed to hold the relay rises. If the control supply is already marginal (see dimension 2), the relay may chatter or drop out. Worked consequence: A G2R-2 installed in a crowded control panel with a VFD that dissipates 200 W can see internal ambient of 60°C. At that temp, the G2R’s margin to dropout shrinks. The G7J-4A, with its 85°C rating and larger coil mass, is unaffected. When this flips: In a climate‑controlled cabinet (ambient

Decision Tree: Pick by Failure Mode

Non‑Obvious Insight: The “Socket Trap”

The G2R-2 is available in socket mount, the G2R-1 is PCB-only. The MY4 (4‑pole) is socket mount, the MY2 is PCB-only. Panel builders often choose a socket relay for easy maintenance. But a socket adds two additional contact interfaces (blade‑to‑socket) per pole. In a high‑vibration environment (near a motor, on a compressor), those interfaces can oxidize or loosen, increasing resistance and generating heat. The failure mode shifts from the relay itself to the connection. If you need vibration resistance, the G2R-1 soldered directly to the PCB is actually more reliable than a socketed G2R-2, even though the latter is “easier to replace.” That’s not intuitive, but it’s true for any industrial panel that runs 24/7.

Failure Mode That Reverses the Decision

The G7J-4A is the most robust relay here, but it has a hidden failure mode: its high coil power (1.8 W) and large panel‑mount footprint mean it’s not suitable for densely packed PCBs or for circuits with a limited power budget. If your control system is a small PLC with a 24 VDC, 500 mA supply, adding a G7J uses almost 4% of that budget just for the coil. Worse, the panel‑mount style requires a separate terminal block and wiring — an extra failure point. In that scenario, a G2R-2 with a proper snubber circuit across the contacts will outlast the machine without the overhead. The “best” relay is the one that fits your system failure mode, not the one with the highest absolute rating.

Rule‑Based Summary

• If steady load < 10 A, resistive, ambient < 50°C, tight PCB: G2R-1 (PCB) or G2R-2 (socket).
• If steady load < 5 A, moderate inrush, socket convenience, ambient < 50°C: MY2 or MY4.
• If load > 10 A, high inrush, high ambient, or inductive: G7J-4A.
• If control supply is marginal or long wire runs: step up to MY or G7J for coil margin.
• If vibration is high and you need socket: reconsider — PCB mount may be more reliable.

The datasheet is never wrong, but the failure mode it doesn’t list will be the one that costs you a panel swap. Pick the relay that survives your edge case.

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.