When wiring 2 lights with 1 switch on high-draw circuits (like workshop LED high-bays or outdoor floods), a standard 15A wall toggle will rapidly fail due to inrush current. The direct solution is to use a 30A DPST electromechanical relay (specifically the Omron G7J-2A-P AC120) controlled by a standard low-current switch. This setup isolates the high-inrush load from your wall switch, preventing welded contacts and melted plastic.

The Inrush Problem & Electromechanical Ratings

Modern high-output LEDs use switch-mode power supplies (SMPS). When you flip the switch, the internal capacitors draw an inrush current that can be 50 to 100 times the steady-state draw for a few microseconds. A standard 15A toggle switch (like the Leviton 1451) is only rated for resistive loads; its small copper contacts will arc, pit, and eventually weld shut under repeated LED inrush.

To solve this, we introduce an electromechanical relay. The relay's heavy-duty silver-alloy contacts handle the brute force of the load, while your wall switch only handles the milliamp draw of the relay's coil.

Which rating column governs this load? For LEDs, HID ballasts, or motors, the Inductive/Ballast or Inrush column governs your selection. Never size a relay based on its Resistive (FLA) rating if the load has a power supply or motor.
Table 1: Electromechanical Rating Comparison (120VAC Circuits)
Parameter Standard 15A Wall Toggle Omron G7J-2A-P (30A DPST Relay)
Coil Voltage N/A (Mechanical) 100/120VAC (or 24VAC/VDC variants)
Contact Rating (Resistive) 15A @ 120VAC 30A @ 120VAC
Contact Rating (Inductive) Not rated / ~5A max 10A @ 120VAC (PF=0.4)
Breaking Capacity (Inrush) ~30A peak 120A peak (make) / 30A (break)

Load Type Decision Path

Not all lights behave the same way at turn-on. Use this decision tree to determine which rating column governs your specific installation and whether a relay is strictly necessary.

Table 2: Load Type Selection Decision Path
Load Type Inrush Multiplier Governing Rating Column Component Recommendation
Incandescent / Halogen 10x - 15x (Cold filament) Resistive / Tungsten Heavy-duty 20A Toggle (e.g., Leviton 1221)
LED (Internal SMPS Driver) 50x - 100x (Capacitive) Inductive / Inrush 30A Electromechanical Relay (Contactors for >4 lights)
HID / Metal Halide 3x - 5x (Magnetic Ballast) Ballast / Inductive Lighting Contactor (e.g., Schneider 8903)
Motorized (Exhaust Fans) 6x (Locked Rotor Amps) Motor (HP Rating) Motor-rated Contactor or Heavy-Duty Relay

Coil vs. Contact Wiring & Protection

An electromechanical relay has two completely isolated circuits: the coil side and the contact side.

  • The Coil Side (Control): Terminals A1 and A2. This is an electromagnet. When your wall switch sends voltage here, it pulls the mechanical armature. It draws very little current (typically 10mA to 30mA).
  • The Contact Side (Load): Terminals 11-12 (Common) and 13-14 (Normally Open). This carries the full amperage of your two lights. When the coil energizes, 11 connects to 13, sending power to the lights.
Flyback Protection for DC Coils: If you choose a DC coil variant (e.g., 12VDC or 24VDC) controlled by an ESP32, Arduino, or smart home hub, you must wire a 1N4007 flyback diode in reverse parallel across the A1/A2 coil terminals (cathode to positive). When the coil de-energizes, the collapsing magnetic field generates a massive reverse voltage spike that will instantly fry your microcontroller's GPIO pin. AC coils naturally mitigate this via the AC zero-crossing, though an RC snubber is still best practice for longevity.

Overcurrent Protection Note: Never treat fuses and breakers as interchangeable for high-inrush lighting. A standard fast-acting glass fuse will blow on the first millisecond of LED inrush. You must use a Type C or Type D curve thermal-magnetic breaker (like the Eaton FAZ-C16-2). Type C breakers tolerate 5-10x instantaneous inrush without tripping, whereas a standard Type B breaker or fast fuse lacks this specific time-delay tolerance.

Step-by-Step: Wiring 2 Lights with 1 Switch

For this build, we are wiring two 150W LED high-bay lights (approx 1.25A each steady-state, but massive inrush) using a 120VAC coil relay housed in a deep junction box.

  1. De-energize and Verify: Turn off the 20A Type C breaker at the panel. Verify dead with a non-contact voltage tester and a multimeter (Line to Neutral should read 0V).
  2. Mount the Relay: Secure the relay to the back of a 4x4 or 6x6 steel junction box using its DIN rail or screw-mount flanges.
  3. Wire the Contact Side (Line & Load):
    • Connect the 12 AWG THHN hot (black) from the breaker panel to Terminal 11 (Common) and Terminal 13 (Normally Open) using a wire nut pigtail, so both lights get power when the relay closes.
    • Run 14 AWG THHN from the pigtail to the black (hot) wires of Light 1 and Light 2.
    • Wire all white (neutral) wires together: Panel neutral, Light 1, and Light 2.
    • Bond all bare copper grounds to the steel box and the light fixtures.
  4. Wire the Coil Side (Switch Loop):
    • Run a 14/2 NM-B cable from the wall switch location to the junction box.
    • Connect the switch's Line (hot) to the relay's A1 terminal.
    • Connect the switch's Neutral to the relay's A2 terminal.
  5. Torque and Close: Torque all terminal screws to the manufacturer's spec (usually 12-14 in-lbs for these relays). Ensure no bare copper is visible outside the terminals. Close the box with a solid cover.

Testing Dead and Live

Before throwing the main breaker, validate the electromechanical action on the bench or with a temporary low-voltage feed if using a 24V coil. For a 120VAC coil setup:

  • Dead Test (Continuity): With power off, set your multimeter to continuity/ohms. Place probes on Terminal 11 and 13. It should read "OL" (Open Loop). Manually press the relay's test button (if equipped) or temporarily apply 120V to A1/A2 using a safe bench cord. The meter should now read < 0.1 ohms, confirming solid contact closure.
  • Live Test (Voltage): Energize the main panel. Flip the wall switch. Measure voltage at the light sockets. You should read 114V to 126V (the acceptable range for a 120V nominal circuit). Listen for a clean, single "clack" from the relay. A buzzing or chattering relay indicates a loose neutral on the coil side or a failing shading ring inside the AC electromagnet.

Repair vs. Replace & The Final Pick

When to repair vs. replace? Never repair an electromechanical relay. The contacts are plated with a precise silver-cadmium or silver-tin oxide alloy designed to quench arcs. If the contacts weld shut, pit, or show heavy carbon tracking, filing them down removes this protective metallurgy. This guarantees rapid subsequent failure, extreme heat, and a severe fire risk. Always replace the entire relay unit.

For wiring 2 high-draw lights with 1 switch in a residential or light-commercial workshop, you do not need to overcomplicate the build with industrial DIN-rail contactors. You need a reliable, high-inrush DPST relay in a standard coil voltage.

The Final Pick: Purchase the Omron G7J-2A-P AC100/120 (approx. $18-$22). It provides 30A DPST contacts, a 120VAC coil that wires directly to standard wall switches without needing step-down transformers, and a 120A make-capacity that easily swallows the inrush current of two large LED drivers without welding. Pair it with a Type C curve breaker at the panel, and your switch loop will outlast the lights themselves.