Omron Relay Roundup: Which One Keeps the Efficiency You Actually Planned For

Every relay datasheet shows a coil power figure. You see it, you multiply by the number of relays, and you add that to your panel's heat budget. Then the panel runs hotter than the calculation predicted. The culprit isn't the coil—it's the contact efficiency you can't keep: the voltage drop across the contacts rises as they age, and that lost wattage becomes heat inside the enclosure. If you sized your cooling for the coil alone, you've already made the cost-of-error decision. This roundup looks at Omron relay's G2R, MY, G7J, and the two-pole G2R-2 not by sticker coil power, but by the efficiency you can actually bank on after 100,000 cycles.

1. Contact Voltage Drop After 100k Cycles – The Hidden Heat Source

A fresh relay's silver-cadmium-oxide (AgCdO) contacts drop roughly 0.1–0.15 V at rated current. That's negligible—at 10 A, about 1–1.5 W of contact dissipation. Omron's G2R-1 and G2R-2 both use AgCdO, and the MY series (also AgCdO) produce similar initial losses. But after 100,000 mechanical operations under a resistive load at 80 % rating, the contact surface degrades: arc pitting, oxide buildup, and material transfer raise the voltage drop. For AgCdO contacts at 10 A, a realistic end-of-life drop can reach 0.3–0.5 V [derived from typical relay aging studies]. At 0.4 V and 10 A, you're dissipating 4 W per contact set—four times the fresh-state loss. If your panel has 20 relays, that's 80 W of unplanned heat.

The worked consequence: a panel designed with only coil dissipation (~0.5 W per relay) fails its thermal budget by a factor of 3–4. That drives fan upgrades, derating, or early contact welding. The reversal: for loads below 1 A, contact heating is negligible regardless of aging. Low-current signal circuits won't see this failure mode. But for power switching above 3 A, the contact-drop drift dominates the efficiency you can actually keep.

2. Coil Hold Power vs. Contact Rating – The TCO Lever

The G2R-1 (10 A, 250 VAC) draws about 0.5 W at 24 VDC coil [derived from rated coil voltage and typical resistance]. The MY2 (5 A, 250 VAC) draws similarly. The G7J-4A (40 A, 250 VAC) uses about 1.2 W coil hold power [derived from datasheet coil data]. At first glance, the G7J seems inefficient per contact amp: 1.2 W for 40 A = 0.03 W/A, while the G2R gives 0.05 W/A. But that ignores the contact efficiency from dimension 1. The G7J's AgSnO₂ contacts are more erosion-resistant than AgCdO under high inrush, maintaining a lower voltage drop over life. At 40 A, a 0.1 V difference in contact drop translates to 4 W saved per relay. Over 10,000 hours, that's 40 kWh—enough to justify a higher coil power, especially in a continuously energized panel.

The worked decision: a machine tool cabinet with 8 G7J relays (320 A total switched) will see roughly 32 W less contact heat at end-of-life vs. using a 40 A-rated AgCdO relay (if one existed). That heat reduction may eliminate the need for a secondary fan in a NEMA 4X enclosure. The reversal: if the load cycle is less than 20 % duty (e.g., occasional start/stop), the coil hold power matters more than contact savings. For low-duty applications, the G2R-1 or MY2 wins on TCO.

3. Dielectric Margin and Thermal Headroom – The Unrecoverable Reserve

The G2R and MY series are rated for 1500 VAC dielectric strength, with an operating range of –40 °C to 70 °C. The G7J series offers 2500 VAC and –40 °C to 85 °C. That extra 15 °C and 1000 VAC margin isn't just a spec sheet trophy—it represents real reserve for when contact heating pushes internal temperature beyond ambient. In a panel that sees 55 °C ambient, the G2R's internal temperature can hit 65–70 °C under full load plus aged contacts, leaving only a 5 °C margin to its 70 °C limit. That margin is where creepage failures and coil burnout happen.

The worked consequence: a panel specified for 60 °C ambient with G2R relays leaves zero thermal headroom after contact aging. One relay failure can cascade. The G7J, with its 85 °C limit, still has 15–20 °C of runway. The reversal: if the panel is climate-controlled to 25 °C and sees less than 3 A per contact, the G2R's thermal margin is adequate. The extra cost of the G7J is wasted.

4. Socket vs. PCB Mounting – The Efficiency of Replacement

The G2R-1 and MY2 are available in PCB mounting; the G2R-2 and MY4 come in socket versions. The G7J-4A is panel-mount. From a pure efficiency standpoint, socket relays add a contact interface that can degrade over time (socket pin oxidation, spring relaxation), adding another 0.02–0.05 Ω per contact. For a 10 A relay, that's an extra 0.2–0.5 W of dissipation per contact pair. But socket relays reduce replacement time from 10 minutes (desoldering) to 30 seconds. The TCO calculation flips: if the relay is replaced more than twice in its service life, the socket's higher steady-state loss is offset by reduced downtime and labor. In a 24/7 production line, a 10-minute outage costs more than 0.5 W of extra heat.

The reversal: for a panel with fewer than 50 relays that runs continuously for 10 years (no planned replacements), PCB-mounted G2R-1s will have lower lifetime heat and higher reliability. The socket interface is an extra failure point. Choose socket only when maintenance access is a constraint.

Failure Mode: When the "Efficient" Relay Fails First

A control system using G2R-1 relays (10 A, 1500 VAC dielectric) on a 5 A inductive motor load in a 60 °C ambient cabinet failed after 8 months. Root cause: contact aging raised the voltage drop from 0.12 V to 0.45 V, adding 4.5 W per relay. The internal temperature exceeded 75 °C, causing coil insulation breakdown. Replacing with G7J relays (AgSnO₂, higher dielectric, wider temp range) eliminated the failure. The G2R was not the wrong relay—it was the wrong selection for the thermal envelope. The rule: if ambient exceeds 50 °C or load exceeds 5 A switching more than 50,000 cycles per year, move to a relay with AgSnO₂ contacts and at least 20 °C thermal headroom above the panel's maximum ambient.

Decision Rule: How to Keep the Efficiency You Plan For

Select the relay family using three thresholds:

• Load current G2R-1 or MY2 (PCB or socket per maintenance plan). The contact-drop drift is negligible.
• Load current 3–15 A, ambient 40–60 °C, or cycles > 50k/year: G2R-2 (socket, for replaceability) or G7J-4A if panel space allows. The contact-drop savings offset the higher coil power.
• Load current > 15 A, ambient > 50 °C, or dielectric stress above 1500 VAC: G7J-4A (AgSnO₂, 2500 VAC, 85 °C). The margin is the only way to guarantee the efficiency you planned for after aging.

If you can't measure the actual contact drop in the field, assume it doubles after 50k cycles for AgCdO, and add 10 % to your panel's thermal budget. That's the real efficiency you can keep.

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.