Otis Singleton
Phone lines, also known as telecom lines, carry electrical current and operate at much lower voltages than power lines. The standard POTS (Plain Old Telephone Service) phone line provides a DC current of around 48 volts to power the telephone electronics, which drops to the 3 to 9-volt range when the telephone is in use. While these low voltages are generally safe, it's important to note that phone lines can still carry enough current to cause a mild shock, and tampering with phone wiring without proper accreditation is illegal in some places.
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What You'll Learn
Phone lines carry an electric current
Phone lines do carry an electric current, but it is a very low voltage. The POTS (Plain Old Telephone Service) phone line, with all phones on-hook, measures around 48 volts of direct current (DC). When a telephone on the line goes off-hook, the voltage drops to the 3 to 9-volt range. An off-hook telephone typically draws about 20 milliamps (mA) of DC current to operate, which is guaranteed by telephone companies in the United States. This current is enough to power the telephone electronics and ring the bell or electronic ringer.
The low voltage of phone lines means that they can continue to function even if trees are growing into them or if they are on the ground. However, it is important to note that while telecom lines operate at lower voltages than power lines, they can still be dangerous, and it is recommended to stay at least 10 feet away if there is an issue with the line.
It is also worth mentioning that tampering with phone lines is illegal in some places unless you have the appropriate accreditation or licensing. This is partly because DIY modifications to telephone networks can be dangerous, but also because phone lines are expected to have battery backup during power outages, and excessive power draw could compromise this.
In summary, phone lines do carry an electric current, but it is a low voltage current that is carefully regulated to power telephone functions while also allowing the phone line to continue operating in various conditions.
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Telecom lines are separate from power lines
While phone lines do carry electricity, telecom lines are separate from power lines. This differentiation is important, especially in the event of a line coming down.
Telecom lines, or telephone lines, are attached to poles without insulators, whereas power lines are attached to poles with insulators that prevent electricity from burning the pole. Power lines carry high-voltage electricity, which can cause serious injury or even death if a line comes down. Telecom lines, on the other hand, operate at much lower voltages, typically around 48 volts DC, which drops to the 3 to 9-volt range when a phone is in use. This low voltage means that telecom lines can continue to function even if they come into contact with trees or are on the ground.
The distinction between power and telecom lines is also evident in their physical appearance. Power lines are usually higher up on the pole, while telecom lines are often found underneath, closer to the ground. Telecom lines are also carried on their own smaller poles, separate from power lines. These poles do not have any equipment like transformers or insulators attached to them.
In the event of a downed power line, it is crucial to contact the appropriate authorities immediately due to the danger posed by the high-voltage electricity. However, if a telecom line is down, individuals can contact their local phone or cable provider for assistance.
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Old rotary dial phones shorted the line
Old rotary dial phones worked on a simple yet ingenious mechanism. Each digit on the dial was associated with a series of clicks or pulses. When the dial was turned, it would release and send these pulses down the line. The number of pulses corresponded to the dialled number. For instance, if you dialled '5', the phone would send five pulses. These pulses were then translated at the exchange to connect the call to the desired number. This system is known as decadic dialing.
The rotary dial also served another function: to short-circuit or interrupt the telephone receiver during dialling, preventing an audible clicking noise from being heard by the user. Some telephones included a small dial built into the handset, with a movable finger stop. The user rotates the dial clockwise until the finger stop ceases moving, then releases it. This design, introduced by Western Electric, allowed for a more compact telephone, with the first being the Trimline telephone.
The first commercial installation of a rotary dial system was a 99-line exchange in LaPorte, Indiana, in 1892. It was based on the 1891 designs of Almon Brown Strowger, an undertaker who believed the local operator was directing business to his competitor. His invention laid the groundwork for modern telecommunications and the transition to digital technology. Despite their lack of modern features, rotary dials occasionally find special uses, such as in anti-drug campaigns or for authenticity in historic properties.
The POTS line, or Plain Old Telephone Service, is the standard residence-type phone line. It consists of two wires, the tip and the ring, which provide DC current to power the telephone electronics and AC current to ring the telephone bell or electronic ringer. When a telephone on the line goes off-hook, the voltage drops from around 48 volts DC to the 3 to 9-volt range. An off-hook telephone typically draws about 20 milliamps of DC current, with the remaining voltage drop occurring over the copper wire path and telephone company circuits.
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Legality of using electricity from a phone line
The legality of using electricity from a phone line varies by location. In the United Kingdom, it is illegal to power apparatus other than a telephone from a phone line. This is because the phone line is a battery backup-based system designed to survive power outages. If other devices draw power from the phone line, the system may not be able to withstand power outages.
In the United States, the telephone company guarantees a minimum current of 20 mA, or a "long loop". A "short loop" will draw 50-70 mA, while an average loop will draw about 35 mA. While there do not appear to be explicit laws against using electricity from a phone line in the US, it is advisable to check local laws before doing so.
It is important to note that using electricity from a phone line can have consequences. Drawing more than a few microamps will cause the switch gear to think the phone is off the hook and send a dial tone. If no call is placed, the system will send alert signals and eventually disable the line to prevent battery drain.
Additionally, phone lines operate with low voltage, typically requiring only 6-12 volts at around 30 milliamps. This means that they may not be suitable for powering devices that require higher voltages.
Overall, while it may be technically possible to use electricity from a phone line, it is important to consider the legal implications and potential consequences for doing so.
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Phone lines can be dangerous
The phone lines themselves are not inherently dangerous, but if you come across a downed phone line, it is important to stay away and report it to the local phone company. This is because there is a slight possibility that power lines could fall on phone lines, injecting a high-voltage current into the phone lines and causing serious injury or even death.
In addition, while phone lines have built-in protections, they can still carry an electric current. If you are working with phone lines, it is important to take the necessary precautions, such as disconnecting the wires at the network interface box or cutting them at different lengths and wrapping them with electrical tape.
Furthermore, in some places, it may be illegal to draw more than a certain amount of current from a phone line, as it could affect the battery backup system that is expected to survive power outages. Drawing more current could cause the phone company to disable the line to eliminate the battery drain.
Overall, while phone lines may not carry high voltages, they can still be dangerous, and it is important to take the necessary precautions when working with or coming across downed phone lines.
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Frequently asked questions
Yes, telephone lines do contain electricity. The voltage is usually around 48 volts DC, but this can drop down to the 3 to 9-volt range when a telephone on the line goes off-hook.
While telecom lines operate at much lower voltages than power lines, they can still be dangerous. It is recommended to stay at least 10 feet away if you notice any issues with a telecom line. If you need to cut a phone line, it is recommended to seek professional advice first.
In the United States, the telephone company guarantees a current of no lower than 20 mA. In the UK, it was illegal to power apparatus other than a phone with electricity from a phone line. It is recommended to check local laws before using electricity from a phone line.
POTS stands for Plain Old Telephone Service. It consists of two wires called tip and ring, which provide DC current to power the telephone electronics and AC current to ring the telephone.
