Communication Lost
APC UPS
Severity: MinorWhat Does This Error Mean?
Communication Lost means APC PowerChute software or NMC (Network Management Card) can no longer communicate with the UPS over its USB or serial interface. The UPS itself continues to function normally — this only affects software monitoring and automatic shutdown. Reseating the USB cable, reinstalling PowerChute, or checking the USB port in Device Manager usually resolves it.
Affected Models
- APC Back-UPS series with USB interface
- APC Smart-UPS series with USB or serial interface
- APC UPS with Network Management Card (NMC)
Common Causes
- USB cable disconnected or damaged
- USB port power-saving settings causing the port to suspend the UPS connection
- APC PowerChute service stopped or crashed
- UPS firmware update interrupted the communication link
- Windows USB driver conflict after a system update
How to Fix It
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Unplug and firmly reseat the USB cable at both the UPS end and the computer end. Try a different USB port on the computer.
APC UPS units use a standard USB-B (square) connector on the UPS end. Try a different USB cable if reseating does not help — USB cables can fail internally while looking undamaged.
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Disable USB selective suspend for the UPS port. In Windows, go to Device Manager > Universal Serial Bus Controllers, find the APC UPS, right-click > Properties > Power Management, and uncheck Allow the computer to turn off this device to save power.
Windows USB power management is the most common cause of repeated communication loss on laptops and desktops with aggressive power-saving settings.
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Restart the APC PowerChute service. Open Services in Windows, find APC UPS Service or PowerChute Personal Edition, and restart it.
If the service fails to start, reinstall PowerChute from the APC website. Download the version matching your UPS model and Windows version.
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Check Device Manager for a yellow warning on the APC UPS entry. If present, update or reinstall the driver by right-clicking the device and choosing Update Driver.
A Windows update occasionally replaces or corrupts the APC HID driver. Uninstalling and re-plugging the USB cable forces Windows to reinstall the driver from scratch.
Frequently Asked Questions
Does communication lost affect the UPS protection?
No — the UPS hardware continues to protect your equipment regardless of whether software communication works. Communication loss only means automatic shutdown software cannot function. You will not receive low-battery warnings or graceful shutdown commands from PowerChute until communication is restored.