Understanding Ringer Equivalence Number for Telecommunications

The ringer equivalence number is a crucial concept in telecommunications that helps us understand how many telephones can be connected to a single line without overloading the circuit. It's a measure of how much power a telephone requires to ring.

A typical residential phone requires a relatively low power to ring, around 2.5 watts, which is equivalent to 2.5 units of ringer equivalence number. This means that two phones with a 2.5-unit ringer equivalence number can be connected to a single line without overloading the circuit.

The ringer equivalence number is usually denoted by the letter "R" and is measured in units of power. For example, a phone with a 2.5-unit ringer equivalence number is denoted as R2.5. This notation helps us quickly understand the power requirements of a phone.

A single traditional telephone ringing circuit has a ringer equivalence number of 1, which is equivalent to a 6930 Ω resistor in series with an 8µF capacitor.

The REN of modern telephone equipment can be significantly lower than 1, with some externally powered digital-ring telephones having a REN as low as 0.1.

In the United States, the FCC Part 68 specification defined 1 REN as equivalent to a 6930 Ω resistor in series with an 8µF capacitor.

Modern line-powered telephones typically have a REN of approximately 0.8.

The ANSI/TIA-968-B specification defines 1 REN as an impedance of 7000Ω at 20Hz or 8000Ω from 15Hz to 68Hz.

A phone line loaded with five phones, each with a REN of 1, would have a total REN of 5.

In Canada, the load number (LN) is a crucial specification that must not exceed 100. This number represents the percentage of total load allowed.

The LN is a key factor in determining the maximum load a device can handle.

In Europe, the Ringer Equivalence Number (REN) used to be equivalent to an 1800 Ω resistor in series with a 1 μF capacitor. This was a standard measure of a device's load.

The REN has since been updated to a more stringent standard, with the latest ETSI specification requiring 1 REN to be greater than 16 kΩ at 25 Hz and 50 Hz.

On a similar theme: Network Interface Device

Maximum Ringer Equivalence is a crucial concept to understand when it comes to phone loads on a subscriber line. The total ringer load on a subscriber line is the sum of the ringer equivalences of all devices connected to the line.

Subscriber telephone lines are usually limited to support a ringer equivalence of 5, per federal specifications. Exceeding this limit can cause phone circuits to fail to ring or malfunction.

If the total allowable ringer load is exceeded, the phone circuit may fail to ring or otherwise malfunction. Call waiting, caller ID, and ADSL services are often affected by high ringer load.

Some analog telephone adapters for Internet telephony require analog telephones with low REN, such as the AT&T 210, which has a REN of 0.9B.

The total REN load on a subscriber line is the sum of the REN loads of all devices connected to the line. Subscriber telephone lines are usually limited to support a load of 5 REN or less.

Additional reading: Analog Telephone Adapter

Here's a breakdown of the REN loads of various devices:

Note that modern phones usually use electronic ringers and put significantly less than one REN load on a phone line. This means you can put more than 5 modern phones on a line.

The telephone ringing process is a complex sequence of events that happens behind the scenes when you pick up the phone. The ringer circuit, located in the central office or FTTH ONT, applies the ring voltage to the phone line.

The phone line is monitored by the ringer circuit, which measures the AC impedance or DC resistance it detects on the line. This is done to ensure that the phone line is not overloaded.

If the AC impedance magnitude or DC resistance drops below the ring trip threshold, the ringer circuit stops ringing the phone and another circuit sends out the dial tone on the line.

The total phone load in a home is limited to 5 REN, but telephone standards require that ringer circuits must be able to ring a phone line without ring tripping even when the phone line is loaded with slightly more than 5 REN.

This margin is to ensure that the phone line can be rung even if the phone REN values vary a bit from their specified values. The load level at which the ringer circuit is guaranteed to ring a line without ring tripping is called the ring trip immunity load.

Modern phones usually use electronic ringers and put significantly less than one REN load on a phone line. This means you can put more than 5 modern phones on a line.

Power usage is a key factor in understanding REN. The average power dissipated during ringing is around 2.6 W, which is close to the theoretical calculation of 3 W.

The theoretical calculation assumed a ring voltage with an RMS value of 65 V, but under heavy load conditions, this value drops to 60 V due to internal losses. This updated calculation results in a power dissipation of 2.55 W, which is reasonably close to the measured value.

The ringer circuit monitors the AC impedance or DC resistance on the phone line and stops ringing if the value drops below the ring trip threshold. The ring trip immunity load is the load level at which the ringer circuit is guaranteed to ring a line without tripping, which is slightly above 5 REN.

Average Power Usage is a crucial aspect of power consumption, and it's essential to understand how it works. The average power dissipated during ringing is around 2.6 W, as measured in the lab.

The theoretical calculation for ring power usage is 3 W, but this assumes a ring voltage with an RMS value of 65 V. Under heavy load conditions, the actual RMS voltage drops to 60 V due to internal losses.

The difference between the measured and theoretical values is relatively small, with the updated theoretical calculation for a lower RMS voltage coming in at 2.55 W. This shows that the theoretical calculation is still a reliable estimate, even with a lower RMS voltage.

There are two approaches to detecting ring trip: AC Impedance Magnitude Measurement and DC Resistance Measurement.

AC Impedance Magnitude Measurement is simpler to implement but only works for phone lines of short lengths, specified by GR-909 as 500 feet or less.

DC Resistance Measurement works for any length line but is more difficult to implement in a small, cheap integrated circuit.

The choice of method depends on the phone line length and the desired level of complexity in the implementation.

AC Impedance Magnitude Measurement is sufficient for short-length phone lines like the ones I work with, but DC Resistance Measurement is required for longer lines.

Modern phones usually use electronic ringers and put significantly less than one REN load on a phone line, allowing for more phones to be connected to a single line.

Here are the two approaches summarized:

In FTTH (Fiber-to-the-Home) setups, the ring voltage is crucial for getting your phone to ring. The ring voltage has a frequency of 20 Hz, which is the standard in North America.

The ring voltage is typically trapezoidal in shape, especially on short-distance lines. This shape provides more RMS voltage for a given peak level, but it can cause interference issues on longer lines or when bundled with other phone lines.

A typical ring voltage amplitude is around 85 V, with an RMS value of around 65 V. This is because short phone lines are often rung with a peak voltage around 85 V, while longer lines require voltages above 100 V to compensate for line losses.

Table 2 from the calculations of Ring Trip Threshold for a Short Line summarizes the AC and DC impedance values for on-hook and off-hook phone lines:

The ring voltage is a crucial aspect of FTTH (Fiber-to-the-Home) technology, and it's essential to understand how it works.

The ring voltage has a frequency of 20 Hz in North America, which is the most common frequency used around the world.

This frequency is what allows the phone to ring and alert you to an incoming call. In contrast, other parts of the world use a ring frequency of 25 Hz.

The ring voltage waveform is usually trapezoidal, which is ideal for short-distance phone lines that aren't bundled with other lines. Trapezoidal signals have a lower crest factor and provide more RMS voltage for a given peak level.

However, trapezoidal signals have more harmonic content than sinusoids, which can cause interference issues when operating phone lines over long distances in a bundle of other lines.

The typical amplitude of the ring voltage is around 85 V, which is sufficient for short phone lines. For longer lines, the voltage needs to be higher, typically above 100 V, to compensate for line losses.

Here are the key voltage values you need to know:

The RMS value of the AC voltage is also an important consideration, as it should be at least 40 VRMS to ensure old phones ring loud enough.

FTTH, or Fiber To The Home, is a type of phone line that's less than 500 feet long. This is a short line, and calculations show that it has a clear difference in AC impedance magnitude between on-hook and off-hook phones.

Table 2 summarizes the results of these calculations, which are based on the Fiber/GR-909 standard. Here's a breakdown of the on-hook and off-hook AC impedance magnitude and DC resistances for a short line:

Both AC and DC ring trip detection will work on a short line, but the ring trip resistance value may be different for each approach.

The value of the ring trip resistance is determined by several key factors, including the ring frequency, AC impedance magnitude, and the type of phone system.

For a GR-909-compliant system, you'll often see ring trip resistance values of around 1 KΩ.

In contrast, landline systems usually have ring trip resistance values of around 4 KΩ.

The ring trip resistance value can vary depending on the country's requirements for ring trip immunity.

Here's a rough guide to the ring trip resistance values for different types of phone systems:

FTTH systems are short, which means they have little DC resistance added to the phone's on-hook impedance. This makes it easy to detect when a phone has gone off-hook.