Load control system

An improved luminaire load control system for handling control signals as by converting them into power line carrier communication signals which are transmitted through branch power lines to terminal control units without causing any significant interference to power line installation, the conversion of the control signals is done respectively at a plurality of gate way units mounted on each branch power line and each gate way unit further includes memory unit for storing the information regarding to the connecting status of the terminal unit for sending back the stored information to a central control unit upon receipt of a send back command therefrom. In a specific embodiment of the invention, a plurality of gate way units are mutually connected with specific signal transmission lines for providing the reciprocity control of luminaire loads by installing a plurality of operation command input terminals in each of the branch power line, whereby the control signal is transmitted through the specific signal transmission lines.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a load control system and, more 
particularly, to a system for providing centralized monitoring and/or 
control for a plurality of loads such as luminaire loads (lighting 
fittings) and the like. 
2. Description of the Prior Art 
The disclosure of Japanese Laid-open Patent No. 7,587/1981 is hereby 
incorporated as the prior art by reference. FIG. 1 shows the schematic 
diagram of the prior art load control system illustrated in said 
literature, wherein, 1 denotes a power line, 2 denotes a plurality of 
luminaire loads connected thereto, 3 denotes a plurality of terminal units 
for providing ON-OFF control of the plurality of luminaire loads 2 with 
the use of switching devices such as relay contacts and the like, and 4 
denotes a central control unit to send out control signals to terminal 
units 3 for the control of luminaire loads 2 via a signal transmission 
line 5 whereby a specific address is assigned respectively to each 
terminal unit 3. 
According to the prior art system, a load control signal is transmitted 
first from the central control unit 4. This load control signal consists 
of a base band or a modulated pulse train, more specifically, of a series 
of address pulses having an address data for specifying a required 
terminal unit 3 and a series of control pulses having a control data for 
controlling the respective luminaire load 2 which is connected to the 
selected terminal unit 3. Each terminal unit 3 monitors a load control 
signal which is transmitted through the signal transmission line 5 and 
accepts the load control signal if the address data thereof coincides with 
own address. The terminal unit 3 then decodes the control data contained 
in the accepted signal and provides the required control of the luminaire 
load 2 in accordance through the decoded control data with use of relay 
contacts and the like. Further, there is provided a monitor input terminal 
(not shown) with each of the terminal unit 3, and a signal indicating the 
status of each luminaire load 2 which is connected to the respective 
terminal unit 3 is fed to this monitor input terminal. The signal 
indicating the status of the luminaire load 2 is transmitted to the 
central control unit 4 as monitor input pulses together with address 
pulses indicating the address of the terminal unit 3 and address pulses 
indicating the address of the central control unit 4. The status of each 
luminaire load 2 is monitored at the central control unit 4 by receiving 
the monitor input pulses. 
FIG. 2 is a diagram illustrating the luminaire load control system of the 
prior art being installed in a building facility together with an electric 
power unit. Branch power lines 1a-1d of the main power line 1 are branched 
through 20A rating breakers 6a-6d. According to the law or private 
regulations such as an electric installation engineering standard, the 
capacity at the final end of the power line is specified to 20A when the 
luminaire loads are fluorescent lamps. Connected to each branch power line 
through a terminal unit are luminaire loads. For instance, luminaire loads 
2a-2c are connected to a branch power line la through a terminal unit 3a. 
Generally, in an ordinary building facility, a plurality of breakers 6a-6d 
are installed in an electric power room as one unit of a distribution 
board for centralized control. That is, the branch power lines 1a-1d are 
branched from the electric power room by every 20A electric current 
capacity in a star connection. On the other hand, every terminal unit 
3a-3p is installed in the ceiling in proximity to its respective luminaire 
load in order to shorten the wiring thereto and a signal transmission line 
5 is connected to the terminal units 3a-3p in a transition connection 
whereby the terminal units are connected in series. As is described above, 
according to the prior art system, the breakers 6a-6d and the central 
control unit 4 are gathered for centralized monitor and control. 
The disclosure of Japanese Laid-open Patent No. 64,140/1988 is hereby 
incorporated by referenced in FIG. 3 as another prior art load control 
system. Now referring to FIG. 3, branch power lines 1a-1d are branched 
from the main power line 1. Connected to the respective branch power line 
are a plurality of luminaire loads 2a1-2d2, a plurality of control 
terminals 3a1-3d2 which are connected to respective luminaire loads for 
providing ON-OFF control thereof by utilizing switching means such as 
relay contacts and the like, a plurality of control means made up of 
operation command input terminals 4a1-4d2 for operating the control 
terminals, central control units 4A-4B for sending out control signals to 
said control terminals 3a1-3d2 upon receipt of signals from said operation 
command input terminals 4a1-4d2 corresponding to the branch power lines 
1a-1d, and block filters 7 for providing the isolation of a signal for 
power line carrier communication between the main power line 1 and the 
branch power lines 1a-1d. 
According to this type of load control system, in case of controlling a 
luminaire load 2 being connected to a different branch power line, for 
instance, in case of controlling the luminaire load 2a1 being connected to 
the branch power line la from the operation command input terminal 4d1 
connected to the branch power line 1d, the flow of the control is as 
follows. First, an operation command is transmitted from the operation 
command input terminal 4d1 to the central control unit 4B through the 
branch power line 1d in power line carrier communication mode. Second, the 
central control unit 4B then transmits the information in the power line 
carrier communication mode to the central control unit 4A being connected 
to the branch power line 1a, which is connected to the control terminal 
3a1 to be controlled, via the main power line 1 in accordance with the 
contents of the received command. Third, the central control unit 4A which 
has received the information sends out the operation command through the 
branch power line 1a to the control terminal 3a1. Finally, the luminaire 
load 2a1 is controlled by the control terminal 3a1 under the received 
operation command with use of switching means such as relay contacts. 
As mentioned above, numerous prior art systems for controlling luminaire 
loads have been proposed and these systems essentially utilize two line 
systems in wiring, a power line system and a signal transmission line 
system, which has resulted in expensive installation and required wire 
checking for each line system in case of an failure. In order to check 
every terminal unit when the signal transmission line system is out of 
order, for example, the checking has to be done by turning off the power 
to the power line system for the loads which are under the control of the 
terminal units to which the signal transmission lines are wired. 
Particularly, in the case of a single signal transmission line being wired 
to a plurality of terminal units which are in connection with a plurality 
of power lines, all of the power lines have to be powered off during the 
checking period of time. As is clear from the above, there have been many 
problems in the maintenance of the prior art system, such as in its 
complexity and the difficulty of checking failures. 
It is therefore an object of this invention to solve such problems and to 
provide a load control system with less wiring and which is easy to 
maintain. 
It is another object of this invention to provide a load control system 
wherein the maximum time required for a central control unit to detect a 
failure of a terminal unit is shortened and an amount of traffic through 
signal transmission lines is considerably decreased. 
It is still another object of this invention to provide a load control 
system wherein an amount of traffic through power lines is decreased by 
making the reciprocity control possible between terminal units connected 
on a different branch power lines for hastening the control of loads and 
improving the reliability. 
SUMMARY OF THE INVENTION 
In accordance with this invention, an improved luminaire load control 
system is provided for effectively handling control signals without 
significantly interfering with the power line installation. 
The luminaire load control system comprises plurality of terminal units for 
controlling a plurality of loads to be connected to each branch power line 
branched form a main power line, and a plurality of gate way units for 
transmitting load control signals, which are transmitted from a central 
control unit through a signal transmission line, to the terminal units by 
converting them into power line carrier communication signals. 
According to the specific embodiment of the invention, each gate way unit 
in the above mentioned luminaire load control system further includes a 
means to confirm the connecting status of each terminal unit to be 
connected to the respective branch power line, a means to store the 
information of connecting status of each terminal unit, and a means to 
transmit the stored information to the central control unit in a lump. 
According to the another specific embodiment of the invention, in the 
luminaire load control system recited above, further included are a 
plurality of control means, one for each branch power line, for 
controlling a plurality of luminaire loads in respective branch power 
line, and a means for providing the reciprocity control between terminal 
units connected in different branch power lines by mutually connecting a 
plurality of gate way units in the branch power lines by using exclusive 
communication lines and by converting a transmission signal for power line 
carrier communication through the branch power lines into a transmission 
signal accommodated to the exclusive communication lines wired for the 
gate way units. 
It is an advantage of the present invention that, since the load control 
signal transmitted from the central control unit is sent to the respective 
branch power line after converting it into a power line carrier 
communication signal at the gate way unit in the respective branch power 
line and the loads connected to the branch power line are controlled in 
accordance with the received load control signal by the respective control 
unit in connection therewith, the power line system and the signal 
transmission system between the gate way units and the respective loads 
can be used commonly for providing the least amount of wiring. Moreover, 
the maintenance relating to the wiring system can easily be carried out 
because, in this arrangement, there is one to one correspondence between 
the branch power line and the signal transmission line with respect to the 
transmission of the control signal to the luminaire loads connected 
thereto. 
In accordance with a specific embodiment of the invention, since the 
connecting status of each terminal unit in connection with a branch power 
line is confirmed and stored by a respective gate way unit provided for 
the branch power line and the stored information of each connection is 
transmitted to the central control unit in a lump from the gate way unit, 
there is no need of polling for each terminal unit in a separated manner 
from the central control unit. Therefore the act of polling is distributed 
and the time required to make a round of all of the terminal units in the 
polling is decreased, thus resulting in the considerable shortening in the 
maximum time required by the central control unit for detecting a failure 
in a terminal unit. Further, with this arrangement, the information 
regarding the wiring connection of each terminal unit can be transmitted 
to the central control unit in a lump from the respective gate way unit, 
therefore amounts of traffic through the signal transmission line is also 
decreased significantly 
According to the another specific embodiment of the invention, in order to 
control a luminaire load from the operation command input terminal unit 
connected in a different branch power line, an operation command is 
transmitted in power line carrier communication mode to the gate way unit 
through the branch power line to which the operated operation command 
input terminal is connected. The gate way unit then converts the received 
the power line carrier communication signal into an exclusive 
communication signal and transmits this converted signal to another gate 
way unit connected to the branch power line to which the control terminal 
to be controlled is connected through the exclusive communication line. 
The gate way unit that has received the converted signal then transmits 
the operation command to the control terminal unit through the branch 
power line. The control terminal unit that received the operation command 
operates switch means in turn for controlling the luminaire load in 
accordance therewith. In this way, this specific embodiment of the 
invention can use exclusive communication lines between gate way units 
different from the prior art system, so that the signal transmission 
between the branch power lines is greatly improved and provided in high 
speed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described more in detail with reference 
to the accompanying drawings. Referring now to FIG. 4, there is shown a 
block diagram of the present invention, the numerals 2-5 identify like 
elements in the prior art system shown in FIG. 1, wherein 8a and 8b denote 
gate way units of each branch power line 1a, 1b for sending out load 
control signals transmitted from the central control unit 4 to the 
respective branch power line 1a, 1b after converting, them into power line 
carrier communication signals. Each terminal unit 3 is connected to the 
respective branched power line 1a, 1b and each gate way unit 8a, 8b is 
assigned an address code respectively in the same manner as terminal units 
3. 
In the operation of the load control system shown in FIG. 4, a load control 
signal is transmitted from the central control unit 4 to the signal 
transmission line 5. As is shown in FIG. 5A, the load control signal 
consists of an originator address code pulse 19a to identify the 
originator, a gate way address code pulse 19b to identify the gate way 
unit that corresponds to the branch power line to which the luminaire load 
2 for the control is connected, a terminal unit address code pulse 19c to 
identify the address data of the terminal unit 3 which controls the 
luminaire load 2, and control data 19d to specify the control for the 
luminaire load 2. Each gate way unit 8a, 8b watches for a signal to be 
directly transmitted through the signal transmission line 5 without 
intermission and will accept the signal if the gate way address is 
indicating its own address. Upon receipt of the address signal, the gate 
way unit converts the terminal address code pulse 19c and the control data 
19d into a transmission signal to accommodated the power line carrier 
communication, modulates a power line carrier wave, and then sends it out 
to the branch power line 1a as is shown in FIG. 5B. In like way, each 
terminal unit watches for a signal to be transmitted through the branch 
power line 1a and will accept the signal if the terminal address code 
pulse 19c is indicating its own address and then controls the respective 
luminaire load 2 in accordance with the contents of the control data 19d. 
The status of the luminaire load 2 is fed to the terminal unit 3 as a 
monitor input signal and sent out to the branch power line 1a as a monitor 
input pulse together with an address code pulse indicating the gate way 
8a. The gate way 8a then accepts the transmitted signal having the address 
code pulse being addressed thereto on the branch power line 1a, converts 
it into a transmission signal for the signal transmission line 5 and sends 
it out to the signal transmission line after adding an address code pulse 
indicating the address of central control unit 4. The status of the 
control of the luminaire load 2 is then monitored at the central control 
unit 4 by receiving the input monitor pulse. 
As it has been described above, by providing the gate way unit respectively 
to each branch power line, it is possible to utilize the branch power 
lines 1a, 1b as control signal transmission lines between the gate ways 
8a, 8b and the respective terminal units 3 in common and less wiring is 
used in installation. 
In FIG. 6, there is shown a block diagram illustrating another embodiment 
of this invention for a luminaire load control system in a building 
installation together with a power line installation. The numerals 1, 
1a-1d, 2a-2c, 3a-3h, 4, 5, and 6a-6d denote like elements in the prior art 
system shown in FIG. 2. The numerals 8a-8d denote gate way units provided 
at each branch power lines 1a-1d. The numerals 7a-7d denote block filters 
for protecting a carrier wave signal for power line carrier communication 
to be used in each branch power line 1a-1d from leaking to different 
branch power lines and for making an impedance of each branch power line 
1a-1d with a capacity of 20 A high against the carrier wave signal. In 
such an arrangement for the luminaire load control system, the branch 
power lines 1a-1d are also used as the signal transmission lines for 
transmitting a control signal to respective terminal control units and the 
luminaire load control is performed in the same way as is described in the 
previous embodiment under the least amount of wiring in the installation. 
Further, as the gate way unit is provided for each branch power line 
1a-1d, the signal transmission line system and the branch power line 
system beyond the gate way units correspond to each other in a one to one 
relationship. Therefore in case of a failure of the luminaire system the 
checking can be performed separately for every branch power line and there 
will be no influence on branch power lines other than the branch power 
line under maintenance as well. 
Generally, the power line carrier communication is considered as a low 
reliable communication system because of the uncertainty of the power line 
characteristics as a signal transmission line. However, in the embodiments 
of this invention, the current capacity branch power lines to be used for 
the power line carrier communication system is limited to 20 A for each 
and limited numbers of luminaire loads are connected. Therefore, it is 
possible to maintain the characteristic of the branch power line as a 
signal transmission line and a high reliable power line carrier 
communication line is provided with appropriate circuit designing. 
Further, in the power line carrier communication system, in order to 
achieve the reliability of the signal transmission, the transmission speed 
of the signal has been kept slow. Therefore, if the terminal units to be 
connected to the power line which is involved in the power line carrier 
communication are increased in number, the communication traffic will be 
increased in turn on the power line and result in the spoiling of the 
response in the load control. However, since in the embodiments of the 
invention, a unit of the power line carrier communication system is 
limited within the scope of the extent defined by the law or regulation 
such as electric installation engineering standard and the like and also 
the numbers of luminaire loads and the terminal units to be connected to 
the power line system are limited as it has been described above, there is 
provided a practical control response system even in such a low signal 
transmission speed condition. 
By utilizing 20 A breakers being capable of ON-OFF switching by remote 
control such as remote control breakers for the breakers 6a-6d shown in 
the embodiment of FIG. 6 and by arranging the remote control breaker 
controllable from the respective gate way units 8a-8d based upon the 
control signals from the central control unit 4, there is provided an easy 
maintenance load control system. For example, a controlled status of the 
luminaire load 2 when the terminal unit 3 is at offset or a controlled 
status of the luminaire load 2 when no control signal is fed is assigned 
as a turn 0N status. With this assignment, the controllability of the load 
control system can be maintained even under such condition as when the 
power line carrier communication system in a branch power line is 
interrupted due to the failure of the terminal unit or other reasons, by 
providing the ON-OFF control with a control breaker under the remote 
control of gate way units 8a-8d to which a control signal is fed from the 
central control unit 4 for simultaneously controlling whole luminaire 
loads connected to the branch power line in trouble. 
The status of connection to each terminal unit 3 in the load control system 
as described above, may be confirmed by sending out a polling signal from 
the central control unit 4 to the signal transmission line 5 for the 
confirmation of the connecting status of the terminal units. The polling 
signal as exemplified by FIG. 7 may consist of an originator address 17a 
indicating the address data for the originator, a gate way address 17b 
indicating the address data for the gate way units 8a-8b that correspond 
to the branched power lines 1a and 1b to which the terminal units 3 for 
which status is being confirmed are connected, a terminal unit address 17c 
indicating the address data for the respective terminal unit 3 to be 
confirmed, and a control data 17d for the terminal unit 3 (loop back 
request command herein). 
In order to make polling with such a polling signal as described above, the 
polling signal is send out from the central control unit 4 to each 
terminal unit 3 respectively through the signal transmission line 5. This 
signal is then converted into a transmission signal for the power line 
carrier communication by the respective gate way unit 8a, 8b, and the 
converted transmission signal is received at each terminal unit 3. Each 
terminal unit 3 then transmits a reply signal to the respective branch 
power line 1a, 1b, and sends back the reply signal to the central control 
unit 4 through the respective gate way unit 8a, 8b. 
FIG. 8 illustrates the sequence diagram of the operation stated above, 
wherein three gate way units 8a-8c are utilized. As mentioned above, since 
the signal transmission speed is kept low for attaining the reliability of 
the control, it takes a long time to get through the polling against the 
whole terminal units if a considerable amount of terminal units 3 are 
connected to the branch power lines and there is a possibility of taking 
too much time before detecting a failure of the terminal unit 3 at the 
central control unit 4 and also there is a problem of increasing an amount 
of traffic in the signal transmission line 5. 
According to the next embodiment of this invention, this problem is solved 
by the provision that an amount of traffic in the signal transmission line 
is decreased considerably by giving a specific feature to each gate way 
unit. In this embodiment, the gate way units 8a, 8b, each connected to the 
respective branch power line 1a, 1b and capable of sending out a control 
signal transmitted by the central control unit 4 to the respective 
luminaire load 2 through the signal transmission line 5 after converting 
it into a transmission signal for the power line carrier communication 
includes the following polling functions. They are additionally equipped 
with a function for confirming the connecting status of each terminal unit 
3 connected to the respective branch power line 1a, 1b, and a function for 
storing information regarding the connecting status of each terminal unit 
3 and for sending the stored information to the central control unit 4 in 
lump. 
In accordance with the load control system as equipped with the functions 
as above, the polling for each terminal unit 3 can be done in the 
following steps. The polling signal (control signal for luminaire loads 2) 
is sent out from the gate way unit 8a, 8b respectively to the branch power 
line 1a, 1b, wherein the polling signal consists of a terminal unit 
address 17a and a control data 17d (herein a status data send back request 
command) as is shown in FIG. 9a. Each terminal unit 3 watches for the 
polling signal being sent out through the branch power line 1a, 1b and 
accepts the polling signal if the terminal address 17c coincides with its 
own address to perform the required process (herein the process for 
sending back the status of the terminal unit 3 to the respective gate way 
unit 8a, 8b) based upon the contents of the control data 17d. 
At the terminal unit 3 that received the polling signal, the terminal 
address 17c and the control data 17d are replaced respectively with a gate 
way address 8a, 8b and a data representing the status of the terminal unit 
3 for the sending back through the branch power line 1a, 1b. In this case, 
the gate way units 8a, 8b also watch for transmitted signals over the 
branch power lines 1a, 1b and are enabled to accept the data representing 
the status of the connection transmit; ted from the terminal unit 3 to 
which the request command is addressed. 
Further, a polling signal consists of a gate way unit address 17b and a 
control data 17d shown in FIG. 9b which may be substituted for the 
structure of the polling signal in the above. 
Referring now to the FIG. 10, a presently preferred structure of the gate 
way unit in accordance with this invention is shown as a block diagram. 
One gate way unit 8a is shown, however, the others have the same 
structure. Block 9a is a signal transmitter receiver unit for exchanging a 
signal between the gate way unit 8a and the central control unit 4 through 
the signal transmission line 5, block 10a is a power line carrier 
communication signal transmitter receiver unit for carrying out the power 
line carrier communication with the terminal units 3 through the branch 
power line 1a, block 11a is a control unit for performing the control of 
the related units, and block 12a is a memory unit to store information 
such as the status of terminal units 3. 
Since the above illustrated gate way unit 8a can store the status of each 
terminal unit 3 connected to the branched power line 1a in the memory unit 
12a, it is possible to send back the stored status information of the 
terminal units 3 to the central control unit 4 in a lump when the control 
signal to request the polling of the terminal units 3 is transmitted from 
the central control unit 4. This eliminates the polling for the terminal 
units 3 to carry out one by one from the central control unit 4 and then 
distributing the steps of the polling as well as decreasing the time 
required to make a round of polling of the terminal units 3. Therefore, 
the maximum time required to detect an irregularity in the terminal units 
3 by the central control unit 4 is considerably decreased in this 
preferred embodiment of the invention. 
Moreover, in accordance with this preferred embodiment of the invention, 
amount of traffic on the signal transmission line 5 is greatly decreased. 
A sequence diagram for polling according to the preferred embodiment 
illustrated in FIG. 10 is shown in FIG. 11. As seen, the amount of traffic 
between the central control unit 4 and each gate way unit 8a-8c is 
distinctly decreased from that of FIG. 8 and this then decreases the time 
required after the polling signal has been transmitted and the send back 
signals carrying the status information of the terminal units are 
collected at the central control unit 4 even if the terminal units 3 are 
increased in number. This is because each gate way unit has added the 
polling function as has been described in the foregoing. 
Still another preferred embodiment of the invention is shown in FIG. 12, 
wherein the blocks 1-5, 7 are the like elements shown in FIG. 3 and blocks 
8a-8d are a plurality of gate way units provided for the branch power 
lines 1a-1d correspondingly. The numeral 13 denotes a specific signal 
transmission line installed in between the plurality of gate way units 
8a-8d. 
In this preferred embodiment of the invention, plurality of control means 
comprise a plurality of terminal control units 3a-3d2 for controlling a 
plurality of respective loads 2a1-2d2 and a plurality of operation command 
input terminal units 4a1-4d2 for transmitting operation commands to the 
respective gate way units through the branch power lines 1a-1d. With the 
help of the gate way units 8a-8d and the specific signal line 13 
inter-connecting the gate way units 8a-8d, the power line carrier 
communication signals on the branch power lines 1a-1d are converted into 
transmission signals accommodated to the specific communication, and the 
reciprocity control amongst the components such as the control terminal 
units 3a1-3d2 connected to the branch power lines 1a-1d, the operation 
command input terminal units 4a1-4d2 and the like, can be performed. 
Further, in this type of load control system, the reciprocity control of 
the luminaire loads 2 connected to any two of the branch power lines 
1a-1d, for example, the control of the luminaire load 2a1 connected to the 
branch power line 1a from the operation command input terminal unit 4d1 
which is connected to the branch power line 1d, can be done in the 
following steps. An operational information is transmitted to the gate way 
unit 8d from the operation command input terminal unit 4d1 as a power line 
carrier communication signal through the branch power line 1d. The gate 
way unit 8d which received the operational information converts the power 
line carrier communication signal into a transmission signal for the 
specific signal line and then the converted operational information is 
transmitted through the specific signal line 13 to the gate way unit 8a 
connected to the branch power line 1a to which the control terminal unit 
3a1 to be controlled is connected. In the next step, the gate way unit 8a 
which received the converted operational information sends out the 
operation command to the control terminal unit 3a1 through the branch 
power line 1a. Hence, the control terminal unit which received the 
operational command controls the luminaire load 2a1 in accordance with the 
command by operating the switching means such as relay contacts and the 
like. 
In this preferred embodiment of the invention, the signal transmission 
between the branch power lines is carried out by utilizing the specific 
signal line, so that, there provided is a high speed communication and 
also the time duration from the request of control by the operation 
terminal unit to the commencement of the control is kept substantially 
constant regardless of the number of branch power lines as well as the 
number of requests to carry out. In other words, there is provided a 
considerable decrease in waiting time. 
Further, in an application of this preferred embodiment of the invention to 
a large scale load control system such as a system to be used in a 
building installation, since the signal transmission between the branch 
power lines can be carried out through the specific signal line wired 
therebetween, there is no need for power line carrier communication 
signals to be transmitted through the main power line and this results in 
the elimination of block filters to be installed in the load only branch 
power lines for blocking off the power line carrier communication signals. 
It Should be appreciated from the foregoing description that the present 
invention provides an improved load control system for controlling a 
plurality of luminaire loads connected to a plurality of branch power 
lines with use of a plurality of gate way units, each of which can afford 
to transfer a control signal into a power line carrier communication 
signal, mounted respectively to each of the branch power line. 
In another preferred embodiment of the present invention, each gate way 
unit further can, afford to store the information after confirming the 
status of connections to the terminal units and to send back the stored 
information in a lump to the central control unit upon request. 
In still another embodiment of the present invention, the plurality of gate 
way units can afford to perform the reciprocity control by connecting the 
gate way units mutually with a specific signal line. 
The present invention is not to be considered to be limited to the specific 
embodiments illustrated, except insofar as may be required by the 
following claims.