10 pin RJ50 (10P10C) male connector to the APC cable
4 pin USB A or USB B plug connector to the PC
The APC USB cable (part number 940-0127, also sold as AP9827) connects a computer’s USB port to the UPS communication port on Back-UPS CS and ES models. It carries simple signalling only — discrete voltage levels indicating on-battery and low-battery states, with no serial protocol — via a USB-to-serial bridge inside the cable body. The computer end uses a standard USB 2.0 Type A plug (4 pins: VBUS, D−, D+, GND), whilst the UPS end uses a 10-pin RJ50 (10P10C) modular plug. The RJ50 is required rather than the physically similar RJ45: the RJ50 has ten contacts and the UPS port uses pins 9 and 10, which fall beyond the eight contacts of an RJ45.
| APC Pin | USB Pin | Description |
|---|---|---|
| 1 | 1 | USB +5V (red wire) |
| 4 | shield | chassis ground |
| 7 | 4 | USB GND (black wire) |
| 9 | 2 | USB Data- (white wire) |
| 10 | 3 | USB Data+ (green wire) |
Notes
- The UPS end of this cable is a 10-pin RJ50 (10P10C) modular plug, not the more common 8-pin RJ45. An RJ45 plug only reaches pin 8 and cannot make contact with pins 9 and 10, which this cable requires.
- This cable implements simple (dumb) signalling only. It is listed in the Schneider Electric PowerChute Serial Shutdown installation guide as the USB option under Simple Signalling cables, not under Smart Signalling. The UPS communicates by asserting discrete voltage levels on handshaking lines; no serial protocol is used.
- The cable contains an internal USB-to-serial bridge chip that presents a virtual COM port to the operating system.
Signals
- USB +5V — bus power from the host; supplied by the USB port (red wire, APC pin 1 to USB pin 1)
- Chassis ground — cable shield connected to APC pin 4 (common) for EMC bonding
- USB GND — signal ground (black wire, APC pin 7 to USB pin 4)
- USB Data− — USB differential data line D− (white wire, APC pin 9 to USB pin 2)
- USB Data+ — USB differential data line D+ (green wire, APC pin 10 to USB pin 3)