⚡ proof‑by‑cases: three load profiles
You pick a relay by contact rating, then it welds shut after 600 cycles on a motor start. The rating wasn’t wrong – you were. A 10 A resistive contact can fail at 3 A inductive if you ignore real watts through the arc. This roundup walks through three real‑world cases – heater, small motor, and high‑inrush lamp bank – and maps each to an Omron family (G2R, MY, G7J) using the only spec that matters: switched volt‑amps at the actual load power factor. No generic “best for most people” – each case gives you a different winner.
🔥 1. Resistive heater bank – continuous 8 A at 240 VAC
Case: an industrial duct heater, 8 A steady-state, resistive (PF≈1.0). The switched power is 8 A × 240 V = 1920 VA. Every Omron relay listed below can close and hold that current; the failure mode is contact erosion from arcing at break – which is minimal with resistive loads. But the catch: a heater cycles 3–5 times per hour, 24/7, giving ~35 000 cycles per year. Mechanical life is not the limit; electrical endurance at rated load is.
How the numbers guide you: The G2R‑1 is rated 10 A at 250 VAC; electrical life at 10 A resistive is about 100 000 operations (illustrative, per Omron application notes). The MY2 at 5 A would be marginal (5 A G2R‑1 (10 A) hits the sweet spot – 8 A is 80 % of rating, well inside the safe zone, and the AgCdO contacts handle the low‑energy arc.
The worked consequence: With a G2R‑1 (coil 24 VDC), you pay ~$4–6 per unit (illustrative). A G7J‑4A runs ~$18–22 (illustrative). For a 30‑relay panel, the G2R saves ~$400–500 upfront. That’s real money – and the G2R will still outlive the heater’s service life.
When this flips: If the heater is switched more than 100 000 times (e.g., pulsed temperature control), you need the MY4 with socket‑mount for easy replacement or the G7J for its higher mechanical endurance (≈10 M cycles, illustrative). But at 35 000 cycles/year, neither case applies. For resistive loads ≤9 A, the G2R‑1 wins on cost and adequate endurance.
⚙️ 2. Small motor – 3 A steady, 18 A inrush for 120 ms
Case: a 0.5 HP fan motor, 277 VAC (3 A running, PF≈0.6, locked‑rotor inrush ~6× FLA = 18 A). The steady‑state VA is 3 A × 277 V = 831 VA, but the arc at make is dominated by the inrush – 18 A at PF≈0.4. Contact welding happens during the first half‑cycle if the relay cannot close fast enough or the contacts bounce.
Mechanism: The inrush is not continuous; the relay must survive the peak let‑through current. The G2R‑1 has a max. switching current of 15 A (illustrative, per Omron derating). 18 A exceeds that – repeated inrush will weld the AgCdO contacts. The MY series, also AgCdO, has similar inrush limits. The G7J‑4A (AgSnO₂) is rated for 40 A continuous and handles 60 A inrush (illustrative).
Worked consequence: Using a G2R‑1 on this motor gave a mean‑time‑to‑weld of ~1 200 cycles (illustrative, based on field reports). Replacing with a G7J‑4A (panel‑mount, 24 VDC coil) eliminates welding for >100 000 cycles. The cost delta (~$14/unit) is trivial compared to a single line‑down hour.
When this flips: If the motor has a soft‑starter that limits inrush to 5× inrush and >500 cycles/year, you must move to the G7J.
| Component | Continuous rating | Inrush capability | Motor verdict |
|---|---|---|---|
| G2R‑1 | 10 A | ~15 A (illustrative) | ❌ too low inrush |
| MY2 | 5 A | ~8 A (illustrative) | ❌ undersized |
| G7J‑4A | 40 A | ~60 A (illustrative) | ✅ safe |
💡 3. Halogen lamp bank – 200 A inrush on 8 A steady
Case: 8 A continuous at 120 VAC, but cold filament inrush reaches 200 A for 8 ms (≈25× steady). The steady‑state power is 960 W; the peak let‑through is enormous.
The spec that controls: No electromechanical relay in this roundup can switch 200 A without contact welding – the arc energy is too high. The G7J‑4A (40 A cont. rating) can survive occasional 200 A peaks if the relay is derated by 70 % for tungsten loads (per Omron application notes, illustrative). Even then, expected life may drop to first closure.
Worked consequence: For lamp banks, the only safe approach is a zero‑crossing solid‑state relay – not any of these electromechanical parts. If you must use a mechanical relay, the G7J‑4A with a 50 % over‑rating (i.e., use a 40 A relay for an 8 A tungsten load) gives a few thousand cycles, but that’s a maintenance trap.
When this flips: If you add an NTC inrush limiter that cuts the peak to
📊 Roundup: which relay for which real‑watt case?
| Load type | Real‑watt constraint | Best Omron family | Why |
|---|---|---|---|
| Resistive heater (≤9 A) | Steady‑state current | G2R‑1 | Cost‑effective, adequate endurance |
| Motor, inrush >15 A | Peak let‑through | G7J‑4A | High inrush margin, AgSnO₂ |
| Tungsten lamp bank | Cold filament inrush | None (use SSR) | 200 A peak exceeds all |
| Any load with >10 A continuous | Thermal rise | G7J‑4A | 40 A rating, panel mount |
| Socket‑mount convenience | Maintenance ease | MY4 or G2R‑2 socket | Plug‑in replacement |
📐 Rule‑of‑thumb threshold
For any load where the peak inrush exceeds 1.5× the relay’s maximum switching current (or 10 A for G2R‑1, 5 A for MY2, 40 A for G7J), you must move up one family or add external mitigation. If inrush exceeds 3×, use a G7J or a contactor. This is not “depends on your scene” – it’s a hard limit from contact physics.
⚠️ The one failure mode that reverses every recommendation
All the above assumes the relay is mounted in a ventilated enclosure. If the ambient temperature exceeds 70 °C (G2R/MY limit) or 85 °C (G7J), the coil insulation degrades and the contact resistance rises. A G2R‑1 that works at 8 A in a 25 °C panel will fail after 200 cycles at 70 °C. The G7J’s wider temperature range (−40 °C to 85 °C) makes it the only choice for hot environments, regardless of load current.
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.
