A cord circuit is a telephone exchange where connections are completed manually, with cords plugged into the appropriate jacks. This approach to telecommunications was historically used at switchboards and junctions to complete calls until the number of telephone subscribers and advances in technology made it obsolete. Today, computerized switching has replaced this mechanical approach in most regions of the world. Some examples of cord switchboards can be seen in settings like films and television shows set in an era when this technique was still in use.
An operator seated at a cord switchboard has a number of jacks connected to local customers along with access to a trunk line to relay long distance calls. When a customer picks up the phone, an indicator light goes on, informing the operator that someone wants to complete a call. The operator plugs a cord into the customer’s jack and presses a speaking key to talk directly with the customer and determine how to route the call. For local calls, the other end of the cord can be plugged into the right jack. Long distance calls would require a connection with the trunk line and the larger telecommunications system.
In addition to being used by the telephone company at local exchanges and junctions, the cord circuit was also used by large companies with their own private exchanges. Such connections allowed companies to maintain a number of lines for workers, using them for both internal and external communication. At the telephone switchboard, operators were available to connect people in the office with each other, place outgoing calls, and process incoming calls.
These circuits provided a means of routing calls to a variety of locations, but there were some limitations. Operators could only handle so many calls at once and might be restrained by the available jacks or cords. As telecommunications subscribers grew in numbers, the cord circuit presented a number of obstacles. Customers might wait unacceptably long to place calls, or couldn’t place an order for phone service because the local switchboard couldn’t support them. Changes in technology led to the adoption of other switching techniques to complete phone calls.
One notorious disadvantage of the cord circuit, for customers, was the operator’s ability to monitor calls. This was sometimes necessary to determine when to terminate the connection, or to intervene in the event of a problem. It also resulted in a lack of privacy, as telephone operators could listen in on discussions through the cord circuit.
By Mary McMahon
Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a About Mechanics researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.