Complete Guide to Generac Load Shed Module Wiring Schematic and Installation

Install the RMU8 auxiliary relay kit alongside the transfer switch for seamless integration. Connect terminals L1 and L2 on the relay board to the corresponding L1 and L2 outputs on the main breaker panel–use 12 AWG copper wire rated for 60°C minimum. Verify tightness with a torque screwdriver set to 18 in-lbs to prevent overheating at connection points. Jumper COM to NO on the relay if pairing with a Smart Management Module; omit this step for standalone relay setups.

Route control wiring through 1/2″ liquid-tight conduit from the relay to the generator’s 12-pin connector. Match pin assignments per label: C1 (battery +), C2 (engine start), C3 (ignition), C4 (chassis ground). Use shielded 18 AWG wire for pins C5–C8 (signal inputs) to eliminate interference from inductive loads. Terminate shield braid at a single ground point on the generator frame–never splice it.

Test the circuit with a multimeter before closing panels. Set meter to 20VDC; probe C1 and C4–expect 12.6–14.4V at rest. Cycle the engine; C2 should pulse to 12V for 500ms (±50ms). If readings deviate, inspect fuses F1 (2A) and F2 (5A) in the control box; replace with identical Littelfuse 451 series. Confirm coolant temperature sensor feedback by monitoring C7–voltage should drop below 0.5V when engine reaches 165°F (±5°F).

Attach priority loads in descending order: medical devices (max 30A), refrigeration (20A), lighting (15A). Use separate branch circuits; never exceed 80% of circuit breaker ratings. For 240V loads, connect across L1/L2 with a double-pole breaker–label clearly to prevent cross-connection errors during maintenance. Document all changes in the equipment log with wire colors, breaker sizes, and test voltages.

Automatic Power Management Connection Guide

Install the priority switching unit by connecting terminal L1 on the transfer switch to the first input contact of the auxiliary controller. Use 12 AWG copper wire for circuits under 20A and 10 AWG for 30A systems–verify local codes for exceptions. Label each wire at both ends with heat-shrink tubing marked “P1,” “P2,” and “COM” to prevent misidentification during maintenance.

Critical Configuration Steps

• Set the control board dip switches: switch 1 ON (enabled), switch 2 OFF (non-critical), switch 3 ON (momentary). This assigns Circuit A as non-essential and Circuit B as secondary priority.
• Ground the neutral bus bar to the main service panel using a 6 AWG bare copper conductor–attach within 6 inches of the controller housing with a listed ground clamp.
• Test the voltage sense lines by probing the control terminals with a multimeter: expected reading should be 120V ±5% between SENSE and neutral.

For split-phase systems, wire the backup power regulator as follows: connect R and W terminals on the external relay to the generator’s start leads–polarity reversed at the relay risks damaging the exciter winding. Jumper the T1 and T2 contacts on the main breaker with a 250V, 40A fuse-rated link bar; omit this step if using a solid-state breaker model (check nameplate for “SS” designation).

Step-by-Step Guide to Identifying Power Management Unit Connection Points



Begin by locating the device’s labeling sticker, typically affixed to the housing or near the terminal block. Manufacturer markings will denote each connector point with alphanumeric codes–common examples include “L1,” “N,” “G,” or numeric sequences like “1,” “2,” “3.” Verify the accompanying documentation for a schematic mapping these codes to their specific functions, such as input, output, grounding, or control circuits. If no sticker is present, use a multimeter in continuity mode to trace connections from known reference points, such as the main breaker or neutral busbar.

Isolate the terminal block by disconnecting all power sources and capacitor discharge. Identify the primary phase terminals first; these usually handle the highest current and are larger or spaced farther apart than auxiliary connectors. For instance, lines supplying external devices often use brass or copper screws, while sensing or signal leads may employ smaller, silver-plated fasteners. Mark each terminal with removable labels or colored tape to prevent miswiring during testing or installation.

Next, focus on the neutral and grounding pads. The neutral terminal will typically align with the system’s white or uninsulated wire, while the ground pad connects to green or bare conductors. Measure resistance between these pads and known ground references–such as the enclosure or earth rod–to confirm proper bonding. A reading near zero ohms indicates correct identification; higher values suggest a loose connection or mislabeled terminal. For units with dual-voltage capabilities, expect additional neutral links that must be bridged per the manufacturer’s specifications.

Test control terminals by energizing low-voltage circuits with a 12V or 24V power supply. These are often grouped separately and may include relays, logic inputs, or communication ports. Use a voltage tester to probe terminals while activating upstream switches or triggers; for example, if a terminal energizes when a specific breaker closes, it likely handles demand sensing or priority switching. Document each finding in a table, noting voltage presence, signal type (AC/DC), and the corresponding device function. Cross-reference this with the schematic to resolve ambiguities.

Final validation involves full system integration under simulated conditions. Reconnect power incrementally, monitoring each terminal with a clamp meter for current flow and transient events. Abnormal readings–such as voltage drop or unexpected phase shifts–may reveal misidentified connectors. Lock down all fasteners to torque specifications (usually 10-15 in-lbs) to prevent loosening under vibration. Store the annotated schematic and terminal map adjacent to the unit for future reference or troubleshooting.

Integrating Several Power Relay Units with a Single Current Management Controller

Begin by installing a dedicated sub-feeder panel rated for the combined capacity of all connected automatic changeover devices. Each relay must draw power from this sub-panel through individual circuit breakers sized to the maximum amperage of the feeder wires, plus 25% headroom for surge protection. Use 10 AWG copper conductors for relays under 30A and 8 AWG for those rated up to 50A, ensuring the sub-panel’s main breaker does not exceed 125% of the controller’s maximum input rating.

Route the neutral wires from each transfer switch to a shared busbar within the sub-panel, then connect this busbar to the controller’s neutral terminal using a single 6 AWG copper conductor. Avoid daisy-chaining neutrals between relays to prevent ground loops. The controller’s ground terminal should be bonded to the sub-panel’s grounding bar with an identical 6 AWG conductor, then linked to the building’s grounding electrode system with no intermediate splices.

Label each relay’s feeder wires with heat-shrink tubing at both ends to identify the corresponding circuit in the controller’s priority matrix. Use THHN wire for indoor runs and XHHW for outdoor conduit installations, ensuring all bends comply with a minimum 6x wire diameter radius to prevent insulation damage. Terminate the hot wires into the controller’s priority input terminals following the sequence outlined in the manufacturer’s specification sheet–typically L1/L2/L3 for three-phase systems or L1/L2 for single-phase.

Verify compatibility between the controller’s firmware version and each relay’s communication protocol. For Modbus RTU systems, assign unique slave IDs to each relay starting from 1 and ascending sequentially; for proprietary protocols, program the corresponding dip switches or software settings before connecting the data cables. Use shielded Cat5e cable for RS-485 networks, grounding the shield at the controller end only to prevent noise interference.

Test the setup by simulating a grid failure. Activate the controller’s diagnostic function to confirm priority-based sequencing: critical circuits should receive power first, followed by secondary and tertiary circuits with a 5-second delay between stages. Measure voltage drop at each relay’s output terminals under full rated current–acceptable values should not exceed 3% of nominal voltage. If readings deviate, revisit connections at the sub-panel and controller terminals for loose or corroded interfaces.

Document the final configuration with a schematic showing breaker sizes, wire gauges, relay priorities, and termination points. Include the torque specifications for all connections (typically 18-22 in-lbs for 8-10 AWG copper) and schedule annual inspections to retighten terminations, as thermal cycling can loosen compression lugs over time.

Identifying and Resolving Frequent Connection Mistakes in Automatic Transfer Switch Configurations

Check neutral conductor continuity first. Loose or improperly terminated neutral wires at the service panel or transfer switch cause imbalance in voltage readings across phases. Use a multimeter to verify zero potential between neutral and ground at the main bonding point–deviations exceeding 0.5V suggest miswiring. Tighten terminal screws to 15 in-lbs torque and retest. If imbalance persists, inspect for neutral-ground shorts in conduit runs between the panel and switch.

Confirm phase rotation aligns with utility and backup power sources. Reversed phase sequencing triggers alarms and prevents seamless switchover. Attach a phase rotation meter directly to the transfer switch output lugs while both sources are live. If readings mismatch, reverse any two supply conductors on the backup source. Avoid swapping utility-side connections–focus adjustments on the generator input only. Document the correct sequence on the switch’s internal cover for future reference.

Fault Symptom	Likely Cause	Verification Step
Humming or vibration in transfer switch	Loose terminal connections	Torque all lugs to manufacturer specs (typically 20–25 in-lbs)
Premature contactor wear	Voltage sags during switchover	Test for 120% voltage drop across contacts during transition
Intermittent failure to engage backup source	Auxiliary contact misalignment	Check continuity of control wires with switch in both positions

Inspect auxiliary relay coils for correct voltage. Apply 120VAC to the coil terminals–absence of audible click indicates internal failure or incorrect voltage tap. Compare coil voltage rating printed on the relay body with system voltage; mismatch requires immediate replacement. Replace relays showing signs of pitting or discoloration on contacts even if functional–these often fail under load within 10–50 switching cycles.