Two three-gang switch boxes are mounted immediately adjacent and outside the AC entrance breaker panel in the basement. Power is provided by two separate 15 amp circuit breakers  as required by the US National Electrical Code (NEC).

The left duplex outlet and top of the center duplex outlet are connected to one phase, and the right duplex outlet and the bottom of the center duplex outlet are connected to the other phase.

                CR230 lead #1 (black)
                              |
Breaker #1  ---+---  left and top center outlets (hot)

                CR230 lead #2 (red)
                               |
Breaker #2  ---+---  right and bottom center outlets (hot)

            CR230 lead #3 (white)
                           |
Neutral   ----+---  all outlets (neutral)
Ground   --------   all outlets (ground)

The Advanced Control Technologies (ACT) CR230   coupler-repeater has a fuse for the electronics associated with each phase and green and red indicator LED’s which should be accessible and visible, hence the exterior mounting.

ACT's Phil Kingery has written a splendid  explanation of repeater-couplers on this  and the subsequent page.

There is space for two CM11a's but only one CM11a is installed at this time. The CM11a is easily moved from one phase to the other maintaining the same wiring path to the main panel for troubleshooting. RS-232 control signals are provided via a Cat-5 cable terminated with two 4P4C  (" RJ11" )  plugs.

Each outlet in the middle is connected to a different phase and can be used for testing purposes such as viewing/measuring the X10 signal with an oscilloscope  via an ACT ScopeTest2.

This is the third, different installation of a X-10 coupler-repeater. The first Leviton controller  ( model 6201 )  failed while in service and was replaced under warranty after a long delay with a newer model (model HCA02-10E) which quickly earned a reputation for being squirrelly . The wallboard shows evidence of being reworked several times -- with increasing impatience ... ;-) 

X-10  troubleshooting gizmos

ACT Scope Test2, Elk ESM1 and filters

As 'nature abhors a vacuum',  power outlets attract wall-warts.  

The black object near the top is an ACT Scope Test2  for observing X-10 signals on the AC power line with an oscilloscope.

The wall-wart power on the lower-left duplex outlet supply connects to an Elk  ESM1  X-10 signal meter which sits atop a Honeywell humidity meter and thermometer.

(The Honeywell meter can  be purchased at big-box home improvement outlet stores for less than the cost  through electronic parts supply chain of the just the humidity sensor it contains - go figger. Along with a moon-phase calculator and Ouija board, it  might also be useful in trouble-shooting X-10 issues .)

   In most X-10 installations of even moderate complexity, one or more ACT AF120 or similar filters are needed.

Filters are used to isolate and minimize the effect of devices such as computer power supplies, lighting dimmers, and uninterruptible power supplies (UPS's)  that have the side effects of reducing  X-10 signal strength ("signal suckers")  and(or)  introducing noise that interferes with x10 operation.

However much filters may be needed to increase X10 reliability, they further contribute to unsightly "wall acne",   complexity  and cost.

For example, this filter costs about $30 from mail-order suppliers of home automation equipment.