1. The 10 A That Isn’t – Continuous Current vs. Contact Rating
The G2R-1 and G2R-2 both list 10 A at 250 VAC. But that rating is tested per IEC 61810-1 at 23 °C ambient on a single relay, open frame, with fresh contacts. Inside a crowded 60 °C cabinet – well within the G2R’s operating range of −40 °C to +70 °C – the current-carrying capability of the silver cadmium oxide (AgCdO) contacts drops by a roughly 20–25 % derating factor because the contact resistance rises with temperature, and the plastic bobbin and housing conduct heat poorly.
Worked consequence: If you actually push 9 A continuous through a G2R at 60 °C ambient, the contact temperature can exceed 105 °C, accelerating oxidation and reducing life from 100 000 electrical cycles to perhaps 15 000–20 000 cycles. That’s not a speculative failure; it’s the reason many integrators spec a 10 A relay for only 6–7 A in a warm panel.
2. The Coil Watt That Steals Your Margin
Every relay coil dissipates heat. The G2R-1 with a 5 VDC coil draws about 0.9 W at nominal voltage; the MY2 with a 5 VDC coil also draws roughly 0.9 W. That doesn’t sound like much – but put ten G2Rs on a dense PCB with 2 mm spacing, and you’ve added 9 W of internal heat that raises the local ambient by 10–15 °C. Now your derating calculation must use that higher ambient, not the panel’s nominal temperature.
Worked consequence: A design that seemed safe at 70 °C ambient becomes marginal at an effective 82 °C local temperature around the relays. Omron relay’s G7J-4A, rated for −40 °C to +85 °C, gives you a wider thermal headroom – but its coil draws about 2.5 W at 24 VDC, so the trade-off is real. The MY series (socket-mounted) often runs cooler because the socket acts as a small heat sink and the spacing is wider, but the MY4 still dissipates ~1.1 W per relay.
3. The Dielectric That Catches Surges
All three Omron families – G2R, MY, and G7J – are built to IEC 61810-1, but their dielectric ratings differ: the G2R series offers 1500 VAC between coil and contacts; the MY series also 1500 VAC; the G7J series stands at 2500 VAC. That 1000 V difference matters when your relay sees a voltage transient from an inductive load or a nearby lightning strike.
Worked consequence: A 2 kV surge on a 24 VDC line can break down coil-to-contact insulation in a G2R or MY if the clearance is marginal, leading to a shorted coil or welded contacts. The G7J’s 2500 VAC rating means a 2.5 kV peak (roughly 1.8 kV RMS) is handled without flashover. In a panel with frequent contactor switching or long cable runs, the G7J’s extra margin can prevent a catastrophic failure that would otherwise require an external MOV and fuse.
4. AgCdO vs. AgSnO₂ – The Welding Threshold That’s Not on the Datasheet
The G2R and MY families use silver cadmium oxide (AgCdO) contacts; the G7J-4A uses silver tin oxide (AgSnO₂). Both are standard for general-purpose switching, but AgSnO₂ is significantly more resistant to contact welding under high inrush currents – about 3× better in terms of energy to weld, per published studies.
Worked consequence: If your load is a capacitive bank or a motor starting with 30 A inrush for 100 ms, an AgCdO relay like the G2R may weld after 5000–10 000 operations, while an AgSnO₂ relay (G7J) can last 30 000–50 000 cycles under the same conditions. The G7J’s 40 A contact rating gives it a huge headroom, but the material itself is the real differentiator for high-inrush applications.
| Relay family | Contact rating (resistive) | Coil power (typical) | Dielectric | Contact material | Best for (eligibility gate) |
|---|---|---|---|---|---|
| Omron G2R-1 / G2R-2 | 10 A @ 250 VAC | ~0.9 W (5 VDC) | 1500 VAC | AgCdO | General-purpose switching, ≤7 A continuous in 50 °C+ cabinet |
| Omron MY2 / MY4 | 5 A @ 250 VAC | ~0.9–1.1 W (5 VDC) | 1500 VAC | AgCdO | Light-duty, socket-mount, low-inrush, ≤4 A continuous |
| Omron G7J-4A | 40 A @ 250 VAC | ~2.5 W (24 VDC) | 2500 VAC | AgSnO₂ | High-inrush / high-ambient (≤85 °C), continuous loads up to 30 A |
Illustrative derating figures based on typical 20–25 % reduction per 30 °C above 25 °C ambient; actual values depend on enclosure, air flow, and duty cycle.
Rule of thumb: For continuous loads above 60 % of rated contact current at ambient >50 °C, choose a relay family with at least one full size step of ampacity margin (e.g., a 10 A load → a 20 A rated relay). For inrush loads >5× rated current (peak), prefer AgSnO₂ contacts and a dielectric ≥2000 VAC. The Omron G7J-4A fits both gates; the G2R or MY fits only when the load is intermittent or well below the margin.
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.
