Tag: RTS Transfer Switch (100A/200A)

A transfer switch that repeatedly trips your main breaker is frustrating and defeats the whole purpose of having a backup generator. The good news: this problem usually has a clear cause, and many fixes are within reach of a homeowner with basic tools and patience.

The Generac RTS (Automatic Transfer Switch) is designed to seamlessly switch your home between utility power and generator power without interrupting service. When it starts tripping the main breaker, it’s almost always because the switch is creating a momentary electrical fault during the transfer process—or the mechanical safety interlocks aren’t working as intended.

At-a-Glance: Most Likely Causes

Cause	Likelihood	Typical Cost to Fix
Momentary paralleling during transfer (utility and generator connected briefly)	Very Common	$
Mechanical interlock worn or misaligned	Common	$$
ATS contacts arcing or pitting during transfer	Common	$$
Inrush current from reconnecting loads (especially motors)	Occasional	$
Neutral switching creating voltage transient	Occasional	$$
Main breaker sensitivity set too low or breaker failing	Occasional	$$

Diagnostic Walkthrough

Follow these steps in order. Start with the cheapest and easiest checks before moving to more involved troubleshooting.

1. Verify the transfer switch is installed correctly. Check that the RTS is mounted securely and all terminal connections are tight. Loose connections at the utility input, generator input, or load output can cause arcing. Use a flathead screwdriver to gently tighten all accessible terminal screws. Do not force them; stop when snug.
2. Inspect the mechanical interlock visually. With the main breaker off and the generator off, look at the moving arm or lever inside the transfer switch. It should move freely and fully engage in both positions (utility and generator). If it sticks, catches, or doesn’t fully seat, the interlock may be preventing proper contact separation. Clean any debris or corrosion with a dry cloth.
3. Check for visible arcing or pitting on the contacts. If you can safely access the switch contacts (consult your manual for access), look for black marks, pitting, or erosion on the metal surfaces. Heavy pitting indicates the contacts are degrading and may need replacement. Do not touch the contacts directly; observe only.
4. Test the transfer sequence manually at low load. With the generator running and the main breaker on, manually switch the RTS from utility to generator and back. Do this slowly and watch the main breaker. If it trips during the switch, note whether it happens during the transition or after. This tells you if the problem is momentary paralleling or a steady-state fault.
5. Reduce the connected load and retry. Disconnect non-essential loads (water heater, HVAC, large appliances) from the circuit and try the transfer again. If the breaker no longer trips with reduced load, the problem is inrush current from high-demand devices. This is often fixable by adjusting the transfer sequence timing or upgrading the generator capacity.
6. Check the main breaker’s amperage rating and trip sensitivity. The main breaker should be rated for the RTS capacity (100A or 200A). If it’s undersized or has a very sensitive trip setting, it may nuisance-trip. Verify the breaker rating matches your RTS model. If it’s correct, the breaker itself may be failing and need replacement.
7. Inspect the neutral connection path. Confirm that the neutral conductor from the utility, generator, and load are properly bonded and not creating a floating neutral during transfer. A floating neutral can cause voltage transients that trip the breaker. Check that the neutral bonding jumper (if present) is secure.
8. Review the RTS control logic and timing settings. Some Generac RTS models allow adjustment of transfer delay and contact closure timing via a control panel. Consult your manual to see if your model has these settings. A longer delay between utility disconnect and generator connect can reduce momentary paralleling. Adjust if available.

Parts You May Need

• Transfer switch contact kit or replacement contacts
• Mechanical interlock assembly (if worn)
• Main breaker (if failing or undersized)
• Neutral bonding jumper or cable
• Dielectric grease (for terminal protection)
• Wire connectors and terminal lugs (assorted sizes)

When to Call a Pro

Contact a licensed electrician or Generac-certified technician if:

• The main breaker trips every time you switch, even with minimal load.
• You see visible arcing or sparks during transfer.
• The mechanical interlock is bent, cracked, or does not move smoothly.
• The transfer switch contacts are heavily pitted or corroded.
• You are uncomfortable working with electrical connections or breaker panels.
• The problem persists after checking all the steps above.
• Your RTS has a control board or microprocessor; these require specialized diagnostic equipment.

Frequently Asked Questions

Why does my transfer switch trip the main breaker only during the switch, not while running on generator?

This is a classic sign of momentary paralleling or contact arcing during the transition. For a fraction of a second, both the utility and generator are connected to the load, creating a fault current that exceeds the breaker’s trip threshold. The mechanical interlock or contact timing may be allowing this overlap. Once the switch completes and settles on one source, the fault clears and the breaker resets.

Can I just replace the main breaker with a higher-amperage one to stop the tripping?

No. Oversizing the main breaker defeats the safety function of the breaker and creates a fire hazard. The breaker should match the capacity of your RTS and home wiring. If the breaker is correctly sized and still tripping, the fault is real and must be corrected at the source—not masked by a larger breaker.

Does a generator that’s out of sync with utility power cause the main breaker to trip?

Yes. If the generator frequency or voltage is significantly different from the utility supply at the moment of transfer, a large inrush current can flow, tripping the breaker. Ensure your generator is running at the correct RPM (typically 3600 RPM for 60 Hz in North America) and that the output voltage is within ±10% of the utility voltage. Check the generator’s control panel for voltage and frequency readings.

Is it safe to keep using the transfer switch if it occasionally trips the main breaker?

No. A nuisance-tripping breaker indicates an electrical fault that the breaker is correctly detecting and interrupting. Continuing to operate the switch without fixing the underlying issue risks equipment damage, fire, or injury. Diagnose and repair the cause before relying on the system again.

Disclaimer

This article provides general troubleshooting information for educational purposes. Always consult your Generac RTS owner’s manual and installation guide for your specific model and serial number. Electrical work can be dangerous; if you are unsure about any step, contact a licensed electrician. Generac and the manufacturer are the authoritative sources for your equipment. For official support, visit https://www.generac.com/support/.

Source: Information adapted from official manufacturer documentation (reference). Always consult your generator owner’s manual for model-specific procedures.

What’s Happening

The Generac RTS (Automatic Transfer Switch) is designed to detect a utility outage, switch your home to generator power, and then switch back to the grid once utility voltage returns and stabilizes. When the utility side fails to reconnect, your home stays on generator power indefinitely—which wastes fuel, prevents the generator from resting, and means you’re not getting the benefit of utility power when it’s available.

This isn’t a generator problem; it’s a transfer switch control issue. The switch itself may be mechanically sound, but the electronics controlling the decision to switch back aren’t working correctly.

At-a-Glance: Most Likely Causes

Cause	Likelihood	Typical Cost to Fix
Return time delay still counting down	Very Common	$0 (wait)
Utility voltage below return threshold	Common	$0–$200 (utility issue or wiring)
ATS utility sensing fuse blown	Common	$$ (fuse + diagnostics)
Relay contacts welded in generator position	Occasional	$$$ (relay replacement)
Control board utility detection circuit fault	Occasional	$$$ (board replacement)

Diagnostic Walkthrough

Work through these steps in order. Most issues are caught early. Stop when you’ve identified the problem, and don’t skip ahead—you’ll save time and avoid unnecessary parts replacement.

1. Check the return time delay setting. The RTS has a configurable delay (typically 5 minutes) that must expire before the switch will return to utility power. This is a safety feature to prevent rapid switching if the grid is unstable. Wait at least 10 minutes after utility power returns, then check if the switch has reconnected. If it has, your problem is solved—you may want to adjust the delay in the control settings if it feels too long. Check your owner’s manual for the exact procedure to view or modify this setting.
2. Verify utility power is actually present at the switch. Use a non-contact voltage tester or multimeter on the utility input terminals of the transfer switch (with the main breaker off for safety). You should see 120/240V (or your local standard). If you see zero or very low voltage, the utility power hasn’t truly returned, or there’s a wiring issue between the meter and the switch. Contact your utility company if the grid is supposed to be up.
3. Check the utility voltage level against the return threshold. The RTS won’t reconnect if utility voltage is below its programmed return threshold (typically 95–100% of nominal). If utility power is present but weak (sagging), the switch is correctly refusing to switch back. This can happen during brownouts or when the grid is recovering. Wait for voltage to stabilize, or contact your utility. You can verify the exact threshold in your manual or by consulting the control board display if your model has one.
4. Inspect the ATS utility sensing fuse. Locate the control board inside the RTS enclosure (you may need to open the door—ensure the main breaker is off first). Find the fuse labeled for utility voltage sensing (typically a small 5A or 10A fuse). Look for a blackened or broken element inside the fuse. If it’s blown, replace it with an identical amperage fuse. A blown fuse prevents the control board from “seeing” utility voltage, so it can’t trigger a reconnection. If the fuse blows again immediately, there’s a short in the utility sensing circuit—stop and call a technician.
5. Check for loose or corroded utility input connections. Turn off the main breaker. Inspect the utility line terminals on the transfer switch for loose, corroded, or burned contacts. Tighten any loose terminals with an appropriate wrench. If you see corrosion (green or white crusty deposits), carefully clean the connection with a wire brush or fine sandpaper, then reconnect. Poor connections can prevent the control board from detecting utility voltage accurately.
6. Listen for relay clicking when utility power returns. If you’re present when utility power comes back, listen near the control board area for a clicking sound. This indicates the relay is attempting to switch. If you hear nothing, the control board isn’t receiving a “reconnect” signal—either the utility sensing is failed or the board itself is faulty. If you hear clicking but the switch doesn’t move, the relay contacts may be stuck or welded.
7. Check the control board for visible damage. With the main breaker off, open the enclosure and inspect the control board for burned components, cracked solder joints, or water damage. If you see obvious damage, the board likely needs replacement. If the board looks clean but the switch still won’t reconnect after all other checks pass, the board’s utility detection circuit has failed internally.
8. Test the manual transfer switch override (if applicable). Some RTS models include a manual lever or switch. Try manually switching to utility position (if safe to do so). If the manual switch works but the automatic function doesn’t, the problem is in the control/relay circuit, not the mechanical switch itself. If the manual switch is stuck or won’t move, the relay contacts may be welded—this requires professional service.

When to Call a Pro

Stop troubleshooting and contact a licensed electrician or Generac service technician if you encounter any of the following:

• Utility voltage is present and stable, but the switch still won’t reconnect after 15 minutes. This indicates a control board or relay failure that requires specialized diagnostics.
• The utility sensing fuse blows again after replacement. A short circuit in the sensing line requires professional repair to prevent damage to the control board.
• You hear the relay clicking but the switch doesn’t physically move. The relay contacts are likely welded or the transfer mechanism is stuck—both require technician service.
• You see water, corrosion, or burned components inside the enclosure. Electrical damage of this magnitude needs professional assessment and repair.
• The control board display shows an error code. Consult your manual for the code meaning, or contact Generac support directly.
• You’re uncomfortable opening the enclosure or working with high-voltage terminals. Transfer switches carry live power even when the main breaker is off. If you’re unsure, call a professional.

Parts You May Need

• Replacement utility sensing fuse (5A or 10A, check your manual)
• Control board (if the board is faulty)
• Transfer relay assembly (if contacts are welded)
• Wire connectors and terminals (for corroded connections)
• Multimeter or non-contact voltage tester

Frequently Asked Questions

How long does the return time delay usually take?

The default return delay on most Generac RTS switches is 5 minutes, but it can be configured from 1 to 30 minutes depending on your model and settings. This delay exists to prevent the switch from rapidly toggling between utility and generator power if the grid is unstable. Check your owner’s manual to see what your switch is set to, and adjust if necessary.

Can I manually switch back to utility power without waiting for the delay?

Some RTS models include a manual override switch or button that allows you to force a switch to utility power immediately, bypassing the delay. However, this should only be done if you’re certain utility power is stable and at the correct voltage. Consult your manual to see if your model has this feature and how to use it safely.

Why would utility voltage be too low to reconnect?

During a grid recovery after an outage, utility voltage may sag (drop below normal) as the power company brings substations back online. The RTS refuses to switch to low voltage to protect your home’s electronics from damage. Once the utility company has fully restored the grid and voltage stabilizes at the correct level, the switch will reconnect automatically.

What does it mean if the relay is clicking but the switch won’t move?

A clicking relay with no switch movement usually means the relay coil is energized (the control board is sending the “switch” command), but the relay’s mechanical contacts are stuck, corroded, or welded together. This is a mechanical failure that requires the relay to be replaced or the switch to be serviced by a technician.

Disclaimer

This article provides general troubleshooting information for the Generac RTS Transfer Switch and is not a substitute for your model-specific owner’s manual or professional service. Always consult the manufacturer’s documentation for your exact model before attempting any repairs or adjustments. Transfer switches operate at high voltage and can be dangerous if mishandled. If you are unsure about any step, contact a licensed electrician or Generac service center. Improper repairs can damage the switch, void your warranty, or create a safety hazard.

Source: Information adapted from official manufacturer documentation (reference). Always consult your generator owner’s manual for model-specific procedures.

What’s Happening?

When your Generac RTS transfer switch hums but fails to actually transfer power from utility to generator (or vice versa), the control board is likely energizing the relay coil, but the physical contacts aren’t moving or aren’t moving far enough to make a solid connection. This is different from the switch being completely silent—the hum tells you the control board is trying to do its job, but something mechanical or electrical is blocking completion.

The good news: this symptom is usually traceable to one of five specific failure modes, and most can be diagnosed with basic tools and a multimeter.

At-a-Glance: Most Likely Causes

Cause	Likelihood	Typical Cost to Fix
Relay contacts stuck or corroded	Very Common	$
Mechanical interlock binding or misaligned	Common	$–$$
Generator voltage too low to trigger transfer	Common	$–$$$
Time delay relay stuck or not timing out	Occasional	$$
Control board relay driver weak or failing	Occasional	$$$

Diagnostic Walkthrough

Work through these steps in order. Stop when you identify the problem.

1. Listen and observe during a transfer attempt. When the utility power drops (or you manually trigger a test transfer), note exactly when the hum starts, how long it lasts, and whether it stops abruptly or fades. Does the hum happen on every attempt? Does it occur when switching back to utility? Document this—it narrows the failure mode significantly.
2. Check generator voltage at the transfer switch input terminals. Use a multimeter set to AC voltage. With the generator running under load (or simulated load), measure the voltage at the generator input terminals of the RTS switch. It should read between 220–240V for a 200A unit or 110–120V for a 100A unit. If it reads below 200V (200A) or below 100V (100A), your generator is not producing sufficient voltage to trigger the transfer logic. Low voltage is a common culprit and often points to a weak generator AVR (automatic voltage regulator) or an overloaded generator.
3. Verify utility voltage is present and stable. Measure the utility input terminals. Voltage should be steady at 220–240V (200A) or 110–120V (100A). If utility voltage is fluctuating wildly or dropping below acceptable levels, the control board may be confused about which source to use. Unstable utility power can prevent the switch from committing to a transfer.
4. Perform a manual transfer test with the generator running. If your RTS has a manual override or test mode (consult your manual for the exact procedure), engage it while the generator is running at full speed. Listen for the hum and watch for any visible movement of the switch lever or contacts. If the lever moves slightly but not fully, or if you hear a grinding sound, the mechanical interlock is likely binding. If there’s no movement at all, the relay coil may not be energizing or the contacts are severely stuck.
5. Inspect the relay coil for signs of burn or corrosion. Open the RTS enclosure (turn off both utility and generator first). Locate the main relay coil—it’s a cylindrical component with wire leads. Look for discoloration, burn marks, or a burnt smell. If the coil appears scorched or smells like burnt insulation, it has likely failed and needs replacement. A weak coil may energize (causing the hum) but lack the force to fully actuate the contacts.
6. Check for mechanical obstruction or corrosion on the contact arms. With power off, gently try to move the main contact arm by hand (if accessible and safe). It should move freely with light pressure. If it’s stiff, stuck, or makes grinding sounds, corrosion or debris is binding the mechanism. Look for white or green oxidation on the contact surfaces. Light corrosion can sometimes be cleaned with a dry cloth or fine contact cleaner; heavy corrosion usually requires contact replacement.
7. Measure the time delay relay output with a multimeter. If your RTS has a visible time delay relay (a small cylindrical or cube-shaped component on the control board), set your multimeter to continuity or resistance mode and test the relay terminals. The relay should switch states (change from open to closed or vice versa) when power is applied and removed. If the relay is stuck in one state, it will prevent the transfer from completing. A stuck time delay relay usually requires replacement.
8. Test the control board relay driver with a load test. This is the most advanced step and may require a technician. If all previous checks pass but the switch still hums without transferring, the relay driver circuit on the control board may be weak. You can perform a rough test by measuring the voltage across the relay coil terminals while a transfer is being attempted. If voltage is present but very low (below 18V for a 24V coil), the driver is likely failing. The control board will need replacement or professional repair.

Parts You May Need

• Main relay coil (RTS-specific; verify part number from your manual)
• Contact kit or contact assembly (for corroded or pitted contacts)
• Time delay relay module
• Control board (if relay driver is confirmed failed)
• Contact cleaner or electrical cleaner spray
• Multimeter (digital, with AC voltage and continuity modes)

When to Call a Pro

Stop troubleshooting and contact a licensed electrician or Generac service technician if:

• The relay coil shows burn marks or smells burnt. Coil replacement requires safe electrical disconnect and proper testing of the control board.
• The contact arm is stuck and won’t move even with gentle hand pressure. Forcing it risks damaging the mechanism further.
• Generator voltage is consistently low (below 200V on a 200A unit). This points to generator failure, which requires specialized equipment to diagnose.
• You measure voltage across the relay coil during a transfer attempt but the contacts don’t move. The relay driver on the control board is likely failing and the board needs replacement.
• You’ve completed all diagnostic steps and the switch still hums without transferring. At this point, the control board or a combination of internal failures requires professional replacement or repair.

Frequently Asked Questions

Why does the switch hum but not transfer?

The hum is the relay coil energizing—the control board is sending power to the coil. However, the physical contacts are either stuck in place due to corrosion, mechanically blocked by a binding interlock, or not receiving enough force from a weakened coil. The control board is trying, but the mechanical or electrical path is broken.

Can I clean the contacts myself?

Light surface corrosion on contacts can sometimes be cleaned with a dry cloth or electrical contact cleaner spray, but only if the switch is fully powered down and isolated from both utility and generator. Heavy corrosion, pitting, or arcing damage requires contact replacement. If you’re not comfortable working inside an electrical enclosure, have a technician do it.

What if the generator voltage is low—does that cause humming?

Yes. If generator voltage is below the threshold needed to trigger the transfer logic (typically around 200V for a 200A RTS), the control board may repeatedly attempt to energize the relay coil without committing to a full transfer. This can sound like a stuttering or continuous hum. Check your generator’s AVR and load balance first.

How long should a transfer take?

A normal transfer from utility to generator (or back) should complete within 1–3 seconds once the control board detects the need to switch. If the switch is humming for longer than a few seconds without completing the transfer, a mechanical or electrical fault is present.

Disclaimer

This article provides general troubleshooting information for homeowners and small contractors. Always consult your Generac RTS Transfer Switch owner’s manual and installation guide for model-specific procedures, safety warnings, and electrical specifications. Transfer switches handle high-voltage circuits; if you are not confident working with electrical equipment, contact a licensed electrician. Improper diagnosis or repair can result in electrical shock, equipment damage, or loss of backup power during an outage.

Source: Information adapted from official manufacturer documentation (reference). Always consult your generator owner’s manual for model-specific procedures.