Load shedding not activating means your transfer switch isn’t automatically disconnecting non-essential loads when generator capacity is exceeded—a safety and equipment protection issue.
What You’re Dealing With
The Kohler RDT MPAC (Modular Programmable Automatic Control) transfer switch is designed to monitor electrical loads in real time and shed lower-priority circuits when demand exceeds your generator’s capacity. When load shedding fails to activate, your genset risks overload, voltage sag, and potential damage to both the generator and connected equipment.
This isn’t a minor inconvenience—it’s a protection system failure. The good news is that most causes are diagnostic-friendly for homeowners with basic tools and patience.
At-a-Glance: Most Likely Causes
| Cause | Likelihood | Typical Cost to Fix |
|---|---|---|
| CT sensors not installed correctly | Very Common | $0–$50 (DIY) |
| Load priority table not programmed | Very Common | $0 (DIY) |
| Communication between ATS and genset lost | Common | $50–$200 (wiring/connector repair) |
| Current threshold set too high | Common | $0 (DIY reprogramming) |
| Load shed relay coil burned | Occasional | $150–$400 (replacement relay) |
Diagnostic Walkthrough
Work through these steps in order. Stop when you find the issue and resolve it before moving forward.
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Verify the load priority table is programmed.
Access the RDT MPAC controller’s display menu (consult your manual for the exact button sequence). Navigate to the load shedding or priority settings. Confirm that at least one load circuit has been assigned a priority level (typically 1–4, with 1 being highest priority and shed last). If the table is blank or shows “Not Configured,” you’ve found your problem. Program the table according to your manual’s instructions, assigning critical loads (refrigerator, well pump, medical equipment) to priority 1 and non-essentials (water heater, pool pump, EV charger) to lower priorities. -
Check CT sensor installation and wiring.
Locate the current transformers (CT sensors) clamped around the main utility or generator feed wires. Verify:- The CT is clamped squarely around the conductor (not at an angle).
- The clamp is fully closed with no gap.
- The wire runs through the CT window in the direction marked by the arrow on the CT body.
- The CT’s output terminals are connected to the RDT MPAC controller’s CT input terminals (usually labeled CT1+, CT1−, etc.).
- No loose or corroded connectors at either end.
Reseated any loose connections. If a CT is damaged or cracked, it must be replaced.
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Inspect the communication cable between ATS and genset.
The RDT MPAC communicates with your generator controller via a dedicated communication cable (often a twisted-pair or multi-conductor shielded cable). Trace this cable from the transfer switch to the genset:- Look for pinched, cut, or abraded insulation.
- Check that connectors are fully seated and locked (if they have locking tabs).
- Verify the cable isn’t routed near high-voltage lines or motor starters that could induce noise.
If the cable is damaged, replace it. If connectors are corroded, clean them with a dry cloth or fine-grit sandpaper and reseat firmly.
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Verify the current threshold setting.
On the RDT MPAC display, navigate to the current threshold or load shedding threshold menu. This value is usually expressed in amps or as a percentage of genset capacity. For example, if your genset is rated 20 kW (approximately 83 amps at 240V), a threshold set to 90 amps means shedding won’t trigger until load exceeds that point. If the threshold is set higher than your genset’s safe continuous capacity, load shedding will never activate. Consult your genset’s nameplate for its rated continuous output in amps, then set the threshold to 80–85% of that value. Adjust via the controller menu and save the settings. -
Test the load shed relay manually (if your controller supports it).
Many RDT MPAC controllers include a test function that energizes the load shed relay without requiring an actual overload condition. Access the service or test menu (often password-protected; check your manual). Select “Test Load Shed Relay” or similar. You should hear an audible click from the relay and see the associated load circuit disconnect momentarily. If there’s no click and no load disconnection, the relay coil may be burned or the relay may be faulty. -
Measure voltage at the load shed relay coil terminals.
With the generator running and the controller powered, use a multimeter set to AC volts. Probe the two terminals of the load shed relay coil (consult your wiring diagram). You should see approximately 120V AC or 24V AC (depending on your controller’s design) when a load shedding condition is triggered or during a test. If you see 0V, the controller isn’t commanding the relay. If you see voltage but the relay doesn’t click, the coil is burned and the relay must be replaced. -
Confirm generator is actually running and producing power.
Load shedding cannot activate if the generator isn’t running or isn’t producing voltage. Start the genset manually and verify it’s running at full speed. Check the RDT MPAC display for a “Generator Running” or “Genset Online” indicator. If the display shows “Generator Offline” or “No Genset Signal,” communication is lost (see step 3) or the genset isn’t actually running. -
Review recent error logs on the controller display.
The RDT MPAC typically logs faults and warnings. Access the history or fault log menu and scroll through recent entries. Look for messages like “CT Sensor Fault,” “Relay Failure,” “Communication Loss,” or “Threshold Exceeded.” These logs often point directly to the root cause and can save hours of troubleshooting.
Parts You May Need
- Current transformer (CT) sensor (if damaged or missing)
- Load shed relay module (if coil is burned)
- Communication cable (if damaged)
- Connector repair kit or individual connectors (for corrosion or loose pins)
- Multimeter (for voltage testing)
When to Call a Pro
Contact a licensed electrician or Kohler-certified technician if:
- The load shed relay coil shows voltage but doesn’t click or engage—the relay is likely burned and requires replacement.
- You measure 0V at the relay coil terminals even when a load shedding condition should be active—the controller itself may be faulty.
- The communication cable is damaged or you’re unable to reseat connectors securely.
- The controller display shows persistent “Communication Loss” or “Genset Offline” errors after you’ve verified the cable and connections.
- You’re uncomfortable working with electrical systems or high-voltage equipment.
Frequently Asked Questions
Why does my generator keep shutting down when I turn on the air conditioner?
If load shedding isn’t activating, your genset is likely hitting its overload limit and shutting down as a safety measure. The air conditioner’s inrush current can spike demand suddenly. Once load shedding is working properly, the controller will shed lower-priority loads (like a water heater or pool pump) before the AC starts, keeping total demand within the genset’s capacity and preventing shutdown.
Can I adjust the load shedding threshold myself?
Yes. The current threshold is user-programmable via the RDT MPAC controller menu. However, it must be set correctly based on your genset’s rated capacity. Setting it too high defeats load shedding; setting it too low will shed loads unnecessarily. Always consult your genset’s nameplate and your controller’s manual before making changes.
What’s the difference between a CT sensor and a regular electrical wire?
A CT (current transformer) sensor is a specialized device that measures the current flowing through a wire without breaking the circuit. It clamps around the wire and produces a proportional low-voltage signal that the controller reads. A regular wire simply carries power. CT sensors are essential for the RDT MPAC to “see” how much load is being drawn and decide when to shed.
If load shedding activates, will my lights flicker?
Possibly, but briefly. When the controller sheds a load, that circuit is momentarily disconnected. You may see a slight flicker in other lights due to voltage recovery. This is normal and lasts only a fraction of a second. If flickering is severe or prolonged, the relay or controller may be faulty.
Disclaimer
This article provides general troubleshooting information for the Kohler RDT MPAC transfer switch. Always consult your model-specific owner’s manual and any technical bulletins from Kohler before performing repairs or adjustments. If you’re unsure about any step, contact a licensed electrician or Kohler support at https://www.kohler.com/support/. Improper installation or repair of transfer switches and generator systems can result in electrical shock, equipment damage, or fire hazard.
Source: Information adapted from official manufacturer documentation (reference). Always consult your generator owner’s manual for model-specific procedures.