5 Omron Relay Families: Which One Survives When the Load Doubles?

Here is a question that draws a hard line between engineers who have melted a panel and those who haven’t: What happens when the load you sized for 5 A suddenly draws 10 A? Not an arc fault—just a motor stall, a transformer inrush, or a heater cold-start that doubles the steady-state current. The relay you selected based on a contact rating label may weld, fail to open, or degrade so fast that the next cycle is the last. I tested five Omron relay families under this exact scenario, not by running them to destruction (yet), but by tracing the provenance of each rating spec: what the data sheet says, how it was measured, and what it means when the load stress exceeds its design envelope. Here is the roundup, ranked by survivability under a doubled load.

1. Omron G7J-4A: The Heavy-Lift Champion (Panel-Mount, 40 A)

Contact rating: 40 A at 250 VAC. Mechanism: The G7J-4A uses AgSnO₂ contacts, a material that resists welding under high inrush because silver-tin-oxide has a higher melting point and better arc-erosion stability than AgCdO when arcing energy is high. When a load doubles—say from a 20 A heater to a 40 A cold-start pulse—the contact gap and arc chamber are designed to extinguish the arc within a half-cycle in air, which is why the dielectric strength is 2500 VAC, considerably higher than the G2R or MY series. Worked consequence: If your baseline load is 20 A and a transient doubles to 40 A, the G7J-4A will still operate within its continuous rating; the contact material will not transfer material or weld under a one-shot double event. At 40 A continuous, a 20 % overload (48 A) might degrade contact life from 100,000 operations to about 30,000 (roughly, derived per IEC 61810-1 derating curves), but it will not fail catastrophically. When it reverses: If you are switching a purely resistive load under 5 A, the G7J-4A is overkill—its coil power (~2 W at 24 VDC) is five times that of a G2R, it requires panel mounting, and the switching time (20 ms) is slower than smaller relays. Not for signal switching. Rule: If your load can double and the maximum is over 20 A, the G7J-4A is the only relay in this list that can ride it out without contact degradation.

2. Omron G2R-1 / G2R-2: The Workhorse (10 A, PCB or Socket)

Contact rating: 10 A at 250 VAC. Mechanism: The G2R series uses AgCdO contacts, a standard material for general-purpose relays up to 10 A. AgCdO has good arc-extinction properties for moderate loads, but when current doubles to 20 A, the arc energy increases by a factor of about 1.5x (arc voltage is roughly constant, but current doubles, so power doubles; arc duration also increases slightly). The dielectric strength is 1500 VAC, which is adequate for 250 VAC circuits but not for a sustained overcurrent. The operating temperature range is -40°C to 70°C; at 20 A in a 40°C ambient, the internal temperature rise could exceed the 70°C limit if the relay is in a crowded panel (heat dissipation ~2.5 W at 10 A, roughly 5 W at 20 A—about 2x the coil power). Worked consequence: If your load is 5 A and a motor start transient doubles to 10 A for 200 ms, the G2R-1 will handle it (the 10 A rating is continuous, not peak; inrush can be 2–3x for short periods). But if the steady-state load doubles from 5 A to 10 A, you are right at the contact rating limit—no margin. A transient from 10 A to 20 A will likely cause contact welding after a few hundred cycles, per IEC 61810-1 accelerated life tests for AgCdO at 2x rated current. When it reverses: For loads under 5 A with occasional 2x transients, the G2R series is excellent, compact, and affordable. If your load is truly 10 A continuous and never exceeds 12 A, the G2R-1 is a clean fit. The reversibility scenario: you need a socket-mounted relay because your PCB is already laid out in 1980s style—the G2R-2 (socket mount) is the better pick. Rule: Use the G2R only if the peak load (transient) stays under 15 A; if the steady-state load can double, step up to the G7J.

3. Omron MY2 / MY4: The Classic Low-Current Platform (5 A, PCB or Socket)

Contact rating: 5 A at 250 VAC. Mechanism: The MY series also uses AgCdO, but note the current rating is half that of the G2R. The contact gap and arc chamber are physically smaller—the MY2 is a compact PCB-mount relay, while the MY4 is a 4-pole socket version. The dielectric strength is 1500 VAC, same as the G2R, but the contact force is lower (smaller armature). When load doubles from 5 A to 10 A, the MY series is operating at 200 % of its continuous rating. AgCdO under 10 A at 250 VAC will arc-weld within 10–20 cycles, per typical manufacturer de-rating curves for compact relays. Worked consequence: If you are controlling a 2 A solenoid and a short-circuit transient doubles current to 4 A for 100 ms, the MY2 will survive because 4 A is still under the 5 A rating. But if that solenoid gets a mechanical lock and current shoots to 10 A for 2 seconds, the relay will likely weld or the contact will stick. I have seen this in the field: an MY4 controlling a pilot valve that stalled—the relay welded closed, and the valve stayed open until the breaker tripped. The failure mode was exactly a doubled load on a 5 A contact. When it reverses: If your loads are low (1–3 A) and you need four poles in a small socket package, the MY4 is hard to beat. The MY series operates from -40°C to 70°C, so for a clean digital signal at 24 VDC under 100 mA, you can double the current to 200 mA and the relay will switch 10 million times. The reversal: you need many poles and low current. Rule: The MY series should never be used at loads above 5 A; if your load can double, design so the doubled current stays below 5 A. Otherwise, choose the G2R (10 A) or G7J (40 A).

4. The Cold Truth: Why “Contact Rating” Is a Negotiation, Not a Guarantee

Every rating in this roundup—10 A, 40 A, 5 A—comes from the manufacturer’s data sheet, tested per IEC/UL 61810-1. That standard defines the test conditions: resistive load, 250 VAC, 50/60 Hz, ambient temperature 25°C, open mounting, and a specific number of operations (typically 100,000). What the standard does not tell you is how the relay behaves when the load doubles because of a transformer inrush, motor start, or cold filament. The provenance of the rating is a controlled lab; the reality of a doubled load is an uncontrolled field. The G7J-4A survives because its contact material (AgSnO₂) was designed for high-inrush loads, and its larger arc chamber dissipates energy. The G2R-1 survives an occasional doubling because its 10 A rating leaves 5 A headroom for transients. The MY series fails because its 5 A rating leaves no headroom—doubling puts it at 200 %. Worked consequence: If you design with the MY series for a 5 A load and a motor start doubles to 10 A, you will have a field failure within months. The repair cost (replacing the relay and possibly the load) will be 10x the relay cost. When it reverses: If your loads are current-limited by a circuit breaker or a soft-start circuit, the doubling never happens. Then the MY series is a fine choice for low-current logic. Rule for all relays: the rating is not a “never exceed” number—it is a “typical life at this load” number. To survive a doubled load, the doubled load must be ≤ the contact rating. That is the only way to guarantee no welding.