10P10C

The 10P10C modular connector type is a type of electrical connector.

This connector type is frequently called RJ50, probably due to the same terminology evolution that led its 8P8C cousin to be best (though incorrectly) known as RJ45. Used correctly, however, RJ50 refers to a specific telephone wiring standard (registered jack) that is just one of the many uses of 10P10C connectors.

A common use of 10P10C is Digi International Digiboard serial connections. It is one of the myriad of RS-232 and RS-485 connectors. See RS-232 for pin assignment.

Another use is with APC uninterruptible power supplies. In this case, it serves only to make the USB connection to the PC incompatible, forcing users with a lost or damaged cable to buy a proprietary one from APC, rather than using an inexpensive and readily-available USB cable with the correct "B" connector on the UPS end. The pinout (at left) also uses both of the outermost positions on the 10P10C connector, preventing an 8P8C Ethernet cable from being spliced onto a USB cable. The connector is also keyed with a tab on one side of the plug to prevent the proprietary cable from being inserted into a network jack.

There is also an RS-232 version of this cable, which has a standard "DB9" (actually DE9) on the PC end. This has pin 2 as TXD, pin 8 as RXD, pin 4 as chassis ground and pin 7 as signal ground. Earlier UPS connections used a DE9 connection on the UPS end as well, just as with other manufacturers, but again deliberately miswired to make the cable proprietary. None of the cables have any other practical use.

This connector is also used by some vendors for expansion modules of their multiport RS-232C serial boards. For example, Cyclades used the pin #1 as a "RI" (Ring Indicator) signal, which is rarely used, allowing an RJ-45 connector to be plugged to their RJ-50 socket for most applications. On the other hand, MOXA uses a different wiring, where they have two pins assigned to a GND (signal ground) signal, and they even do not have the RI signal connected. So with MOXA's pin assignment, users are forced to use a nonstandard RJ-50 connector while not gaining more than eight signals (for which a standard RJ-45 connector would be sufficient).