A manual exchange connects calls through a human operator who plugs a cord between the caller’s jack and the called party’s jack, so the operator necessarily learns who calls whom, at what hour, and often what for. A settlement that builds one should write down, before the first call, what the operator may hear and repeat, how the post is filled and rotated, and who may read any log. A board of 25 cord pairs carries about 100 subscribers who each talk 10 minutes in the busy hour.
Part of Telecommunications
A staffed switchboard connecting subscriber lines by cord, considered as a machine and as a post in the community that holds knowledge about everyone on it.
A Switchboard Is A Post As Much As A Panel
The machine is simple. Each subscriber has a jack and a lamp or drop; the operator sees the signal, answers with a cord, asks for the destination, plugs the other end of the cord pair into the called line’s jack, and rings it. Construction, cord length (0.6 to 1.0 m) and supervision are covered in Manual Switchboard and need not be repeated here.
What the machine cannot do is work without someone listening. The operator has to hear the request to complete it. Switching Systems lists the benefit and the cost in one pair of sentences: the operator can resolve wrong numbers, names against numbers, time-of-day announcements and emergency routing, but there is “no privacy (operator hears beginning of all conversations)“. The same ability is the same exposure.
The Operator Knows The Settlement’s Pattern Of Contact
Without hearing a word of any conversation, an operator sees who rings whom and when. A call at 03:00 from the clinic’s line to a house is information. So is a line that never rings, or two households whose calls always follow a meeting. This is an illustration of the kind of knowledge, not a claim about any real operator, but the knowledge is real whoever holds the post. It gives its holder a form of power:
- Information: who is in contact, how often and when
- Delay or refusal: a call can be put through slowly, or not at all, with no one the wiser
- Emergency priority: a call can be put ahead of others, which is both the good use and the abuse
The corpus treats the same shape of problem for the census: Privacy and Trust says people answer honestly only if they trust the data will not be used against them, and Data Access separates individual records from aggregate figures and recommends logging every access. A switchboard is a small live version of the same issue.
Write The Rules Before The First Call
Four rules cost nothing to adopt and are hard to impose once an operator has habits:
- Duty of confidentiality. The operator may listen only as long as needed to complete the call, repeats nothing outside the post, and discloses who called whom only under a rule the community has agreed in advance.
- A fixed route to the post. Fill it by the method the settlement uses for other community jobs (see Community Roles) rather than by whoever happens to be handy.
- Rotation. Privacy and Trust recommends a discreet community recorder who rotates every 2 to 3 years; the same logic applies. Long tenure concentrates knowledge in one person.
- A named overseer for complaints. Pair the post with a body that can hear a complaint, as in Accountability Mechanisms. The checks that Separation of Powers describes apply at this scale too: whoever runs the board should not alone decide who may inspect it.
If the operator keeps any log at all, decide who can read it, and say so in writing. A log kept for fault-finding is also a record of every conversation pair.
Capacity Is The Operator, Not The Board
The corpus gives different capacities for one operator: 50 to 100 lines in Telephony and 100 to 150 lines at 30 to 40 simultaneous calls in Manual Switchboard. Take the lower figure for planning. Traffic is sized in erlangs: 100 subscribers each talking 10 minutes in the busy hour give 100 × 10 / 60 = 16.7 erlangs, and 25 cord pairs carry that with about 1.5% blocking by the Manual Switchboard article; the Erlang B recursion gives about 1.4%. Nights need a rule too: either the board is staffed or an unattended line falls back to an agreed emergency ring.
What You Need
- A board: a jack and a lamp or drop for every line, cords in pairs, a ringing key and an operator headset
- A ringing source: a hand magneto at 60 to 90 V AC, or a generator at the board
- A written numbering and directory list, so the operator is not the only holder of who is where
- The rules above, signed off by whoever governs the settlement
Common Mistakes
- Treating the post as a neutral job. The operator holds the contact pattern of everyone on the board.
- No night arrangement. The first emergency after hours finds an empty chair.
- Keeping the directory only in the operator’s head. The operator then cannot be replaced or overseen.
- Letting the board outgrow one person. Past a few dozen lines, add a second position, or start the move described in Automatic Switching.
Safety
Ringing voltage on the cord
Pressing the ringing key puts ringing voltage on the called line through the cord and plug; on a local-battery system the line itself may carry 60 to 90 V AC from a subscriber’s magneto. Handle plugs by the insulated body, never complete a ring with a bare hand on a tip, and keep the headset off the ear while keying. Fit the line protectors described in Lightning Protection to every incoming pair.
What’s Next
- Learn next: Automatic Switching, what is gained and lost when the operator is removed
- Combine with: Network Architecture for linking several boards