Phone switchboard, 1974
(also called a manual
) was a device used to connect a group of telephones
manually to one another or to an
outside connection, within and between telephone exchanges
or private branch exchanges
user was typically known as an operator
. Public manual exchanges
disappeared during the last half of the 20th century, leaving a few
PBXs working in offices and hotels
manual branch exchange
The electromechanical automatic telephone exchange
invented by Almon Strowger
gradually replaced manual switchboards in central telephone
exchanges. Manual PBXs have also for the most part been replaced by
more sophisticated devices or even personal computers, which give
the operator access to an abundance of features. In modern businesses
, a PBX often has an attendant console
for the operator, or an
avoiding the operator
The switchboard is usually designed to accommodate the operator to
sit facing it. It has a high backpanel which consists of rows of
female jacks, each jack designated and wired as a local extension
of the switchboard (which serves an individual subscriber
) or as an incoming or outgoing trunk
line. The jack is also associated with a lamp.
On the table or desk area in front of the operator are columns of
keys, lamps and cords. Each column consists of a front key and a
rear key, a front lamp and a rear lamp, followed by a front cord
and a rear cord, making up together a cord
. The front key is the "talk" key allowing the operator
to speak with that particular cord pair. The rear key on older
"manual" boards and PBXs is used to physically ring a telephone. On
newer boards, the back key is used to collect (retrieve) money from
. Each of the keys has three
positions: back, normal and forward. When a key is in the normal
position an electrical talk path connects the front and rear cords.
A key in the forward position (front key) connects the operator to
the cord pair, and a key in the back position sends a ring signal
out on the cord (on older manual exchanges). Each cord has a
three-wire TRS connector
: tip and ring
for testing, ringing and voice;
and a sleeve wire for busy
When a call is received, a jack lamp lights up on the back panel
and the operator responds by placing the rear cord into the jack
and throwing the front key forward. The operator now converses with
the caller and finds out where the caller would like to be
connected to. If it is another extension, the operator places the
front cord in the associated jack and pulls the front key backwards
to ring the called party. After connecting, the operator leaves
both cords "up" with the keys in the normal position so the parties
can converse. The supervision lamps light to alert the operator
when the parties finish their conversation and go on-hook. When the
operator pulls down a cord, a pulley weight behind the switchboard
pulls it down to prevent it from tangling.
On a trunk, on-hook
signals must pass in both directions. In a
one-way trunk, the originating or A board sends a short for
off-hook, and an open for on-hook, while the terminating or B board
sends normal polarity or reverse polarity. This "reverse battery"
signaling was carried over to later automatic exchanges.
Telephone Operator, circa 1900.
The first telephones in the 1870s were rented in pairs which could
only talk to each other, but the example of a central exchange was
soon found to be even more advantageous than in telegraphy
. Small towns typically had the
switchboard installed in the operator's home so that she could
answer calls on a 24 hour basis. In 1894, New England Telephone and
Telegraph installed the first battery-operated switchboard on
January 9 in Lexington,
Early switchboards in large cities usually were mounted floor to
ceiling in order to allow the operators to reach all the lines in
the exchange. The operators were boys who would scoot up a ladder
to connect to the higher jacks. Late in the 1890s this measure
failed to keep up with the increasing number of lines, and Milo G. Kellogg
Divided Multiple Switchboard
for operators to work
together, with a team on the "A board" and another on the "B."
These operators were almost always women until the mid-1960s when
men were once again hired. Early "cord" switchboards were often
referred to as "cordboards" by telephone company personnel.
Conversion to Panel switch
automated operations in big cities first eliminated the "B"
operator and then, usually years later, the "A". Rural and suburban
switchboards for the most part remained small and simple. In many
cases, customers came to know their operator by name.
As telephone exchanges converted to automatic, or direct dial
, service, switchboards remained in
use for specialized purposes. Before the advent of direct-dialed
long distance calls, a subscriber would need to contact the
operator in order to
place a call. In large cities, there was often a special number,
such as 1-1-2, which would ring the long-distance operator
directly. Elsewhere, the subscriber would ask the local operator to
ring the long-distance operator.
When calling long distance, the customer often would not have the
phone number available, so would give the name and city of the
person desired. The long-distance
would plug into a trunk for the distant city, and the
inward operator would answer. The inward operator would obtain the
number from the local information operator, and ring the call. The
calling party's long distance operator would time the call for
Later, with the advent of multi-frequency
operator dialing, the
operator would plug into a tandem trunk line and dial the area code
and operator code for the information operator in the distant city.
If the customer knew the number, and the point was direct-dialable,
the operator could dial the call. If the distant city did not have
dialable numbers, the operator would dial the code for the inward
operator, and ask her to ring the number.
After most phone subscribers had direct long-distance dialing, one
type of operator served both the local and long distance functions.
A customer might call to request a collect call, or help getting
through on a number that did not ring or might be out of order, for
instance. For example, if a customer encountered a reorder tone
(a fast busy signal), it could
indicate "all circuits busy," or a problem in the destination
exchange. The operator might be able to use a different routing to
complete the call. If the operator could not get through, she could
call the inward operator in the destination city, and ask her to
try the number, or to test a line to see if it was busy or out of
order. Cordboards for these purposes were replaced in the 1970s by
and similar systems.
A Virtual Switchboard is an automated system used to connect an
incoming caller with an agent or staff member. The virtual
switchboard user normally has the option of controlling how
incoming calls are routed via a web interface. For example calls
could be routed to different destinations according to certain
criteria such as the time of day etc.
(IVR) functionality is also a common feature with
Virtual Switchboards. IVR enables incoming callers to a Virtual
Switchboard to hear prerecorded announcements. Popular
announcements instruct callers to press a number on their key pad
to select which department they want to reach (for example, "press
1 for sales, 2 for accounts and 3 for support").