- Solar and energy
- UPS (uninterruptible power supply)
Constant Solid Tone
APC UPS Constant Solid Tone: backup outlet overload
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
High
Quick answer
A constant solid tone paired with a solid red Overload LED means equipment plugged into the Battery Backup outlets is drawing more power than your APC UPS can supply.
Safety first
Stop and check this first
- Never plug surge strips or motor-driven equipment into the UPS: APC explicitly warns never to plug outlet strips or surge protectors into any UPS and notes that step-approximated sine-wave backups are not intended for motor-driven equipment.
Safe checks you can perform
- Unplug nonessential loads and move peripherals to Surge Only outlets
- Power on the UPS before turning on connected equipment
- Run APC's 4-step no-load cold-start check
Leave these tasks to a qualified professional
- Do not attempt this professional task: APC Technical Support replacement or authorized service handling
- Do not attempt this professional task: Load wattage audit and outlet reallocation by a technician
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
APC Technical Support replacement or authorized service handling
What they doIf the constant flat tone continues during the no-load test, APC Technical Support or an authorized technician safely decommissions the unit and processes warranty or replacement options.
They must show youDemonstration that the constant flat tone persists with all rear outlets disconnected.
In writingUPS model number, serial number, and APC Support replacement or service reference.
Load wattage audit and outlet reallocation by a technician
What they doA technician measures or calculates the true watt draw of each connected device, removes prohibited power strips or motor-driven loads, and balances computers versus peripherals across Battery Backup and Surge Only outlets.
They must show youMeasured or rated wattage of the attached load compared against the UPS model specification.
In writingDocumented load allocation per outlet bank or sizing recommendation for a higher-capacity APC UPS.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Unplug nonessential loads and move peripherals to Surge Only outlets
- Who:
- You, checking the power cords plugged into the rear outlets of the UPS.
- How:
- Disconnect nonessential high-draw equipment such as printers from the Battery Backup outlets, move secondary peripherals to the Surge Only outlets, and ensure no outlet strips or surge protectors are plugged into the UPS.
- Result that matters:
- Total wattage on the battery-supplied outlets drops within the model's rated capacity and the overload tone stops.
- If the constant tone stops and the red Overload LED turns off once load is reduced:
- the UPS can continue normal operation.
- If the Overload LED stays lit even after verifying load is well below the watt rating:
- turn the unit off and back on, then proceed to the no-load test.
- Evidence to keep:
- List of devices removed from Battery Backup outlets and whether the Overload LED cleared.
Evidence: Video: Why might my APC Back-UPS Product be beeping? · Why might the LEDs on my Back-UPS or Smart-UPS SC be flashing? · What are the basic troubleshooting steps for the Smart-UPS SMT750 / SMT1000 / SMT1500 ?
Power on the UPS before turning on connected equipment
- Who:
- You, when starting your workstation.
- How:
- When the UPS load is close to 80% of battery outlet capacity, do not use the UPS as a master on/off switch: turn the UPS on first, let it finish its 15-second self-test, and then power on your computer and monitor afterward.
- Result that matters:
- Simultaneous startup inrush current is avoided so the Overload LED does not trip during power-up.
- If the Overload LED only flashes briefly at startup and then stays off:
- APC notes this brief illumination from inrush current is normal.
- If the unit emits an uninterrupted constant flat tone:
- perform APC's 4-step unplugged test.
- Evidence to keep:
- Observation of whether the Overload LED clears after staggered equipment startup.
Evidence: Video: Why might my APC Back-UPS Product be beeping? · Why might the LEDs on my Back-UPS or Smart-UPS SC be flashing?
Run APC's 4-step no-load cold-start check
- Who:
- You, following the exact 4-step procedure documented by APC.
- How:
- If reducing the load does not stop the constant flat tone: 1) turn the UPS off, 2) unplug all equipment from the UPS, 3) unplug the UPS from the wall outlet, and 4) push and hold the Power On button until you hear two beeps, releasing the button before the second beep ends.
- Result that matters:
- The UPS either starts cleanly on battery with no load attached or continues emitting a constant flat tone.
- If the UPS goes onto battery and operates normally with nothing plugged in:
- reconnect devices one at a time to identify the overloading piece of equipment.
- If the UPS still emits a constant flat tone with all equipment unplugged:
- APC states the unit was permanently damaged by the overload and you should contact APC Support.
- Evidence to keep:
- Outcome of the 4-step no-load test (normal battery operation vs persistent constant tone).
Evidence: Video: Why might my APC Back-UPS Product be beeping?
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Solar and energy
- Brand
- APC
- Product type
- UPS (uninterruptible power supply)
Known code variants
- Capacity Overload
- Constant, Solid Tone
- LED Overload encendido fijo
- Red Overload LED on solid
- Red Overload LED: on solid
- Shrill constant tone
- Sobrecarga de capacidad
- Tono constante y fijo
What it means
On APC Back-UPS and Smart-UPS SC models, a constant flat or shrill tone with the red Overload LED lit solid signals an overload on the battery-backed outlets. This alarm alone never proves the UPS hardware is defective: it most often happens because connected devices exceed the model's watt rating, printers or nonessential peripherals are plugged into battery outlets, or startup inrush current spiked when powering everything on together, though a tone that persists with all loads unplugged points to internal overload damage.
Warnings and stop conditions
- Highsource verified
Never plug surge strips or motor-driven equipment into the UPS: APC explicitly warns never to plug outlet strips or surge protectors into any UPS and notes that step-approximated sine-wave backups are not intended for motor-driven equipment.
Evidence: Video: Why might my APC Back-UPS Product be beeping? · What are the basic troubleshooting steps for the APC Back-UPS Pro with Networking BG500 ?
Symptoms and causes
Probable causes · in order
- Connected load exceeds the Battery Backup watt ratingCommon
Total power draw from devices plugged into the battery-powered outlets exceeds the maximum volt-amp or watt capacity specified for the APC model.
Evidence: Video: Why might my APC Back-UPS Product be beeping? · Why might the LEDs on my Back-UPS or Smart-UPS SC be flashing?
- Startup inrush current when used as a master power switchPossible
Using the UPS as a master on/off switch especially near 80% load causes simultaneous startup inrush current across connected equipment that briefly triggers the Overload indicator.
Evidence: Video: Why might my APC Back-UPS Product be beeping? · Why might the LEDs on my Back-UPS or Smart-UPS SC be flashing?
- Permanent internal damage following a severe overloadLess common
If the unit continues to emit a constant flat tone even with all equipment and wall power removed, the inverter or output stage was permanently damaged by the overload.
Evidence: Video: Why might my APC Back-UPS Product be beeping?
Virtual technician
Does Constant Solid Tone still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Video: Why might my APC Back-UPS Product be beeping?
Schneider Electric · 2026 · official_doc
- 2
What are the basic troubleshooting steps for the APC Back-UPS Pro with Networking BG500 ?
Schneider Electric · 2026 · official_doc
- 3
Why might the LEDs on my Back-UPS or Smart-UPS SC be flashing?
Schneider Electric · 2026 · official_doc
- 4
¿Por qué parpadean los LED de mi Back-UPS o Smart-UPS SC?
Schneider Electric · 2026 · official_doc
- 5
What are the basic troubleshooting steps for the Smart-UPS SMT750 / SMT1000 / SMT1500 ?
Schneider Electric · 2026 · official_doc
- 6
¿Cuáles son los pasos básicos para solución de problemas de Smart-UPS SMT750 / SMT1000 / SMT1500?
Schneider Electric · 2026 · official_doc
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