A (very) brief history of phones

Traditional copper telephone lines have always carried within them 48V of line voltage – this is actual voltage received from telephone sockets, and which could be used to power a connect phone.

Most analogue handsets worked by using the telephone line as a power supply. The handset was plugged into the wall while the actual receiver was connected via a cable so that the power could pass through.

In the 90’s, when cordless home telephones (Digital enhanced cordless telecommunications or DECT) made their first appearance, the 48V of line power suddenly became less relevant as once the whole handset was lifted out of the cradle, the power supply was cut. The solution was to plug the ‘base station’ part of the phone into a separate mains power supply in order to charge a battery in the cordless handset.

Lift phones and power supply

When emergency lift phones began to be designed, there were two proposed ways of supplying the phones with power:

• Use a separate power supply for the telephone which then allows the phone to draw its own power, charge its own battery and manage its own power circuitry
• Use the “free” 48V supplied by the telephone line to power the telephone

Compliance and EN81-28

The Lifts Regulations 1996 have required that all lifts installed in the UK are fitted with an emergency telephone. Compliance to the regulations is demonstrated by applying designated standard EN81-28. EN81-28 requires that emergency lift phones MUST have enough backup power to function for one hour, with 15 minutes of talk time, in the event of a mains power failure

It has been argued that line powered telephones do not need a backup power supply as, if the phone line itself has failed, the emergency phone won’t be able to dial out anyway. Effectively, the power backup is whatever is available in the line.

Challenges with line powered voltage

Line powered phones are cheap but bring a set of challenges and risks. Fundamentally a line powered unit draws its voltage from the telephone line. It is worth noting that this has two major downsides:

No regulation

Telephone line voltage is poorly regulated so there are a lot of variants on the supply.

In practical terms, this means that the telephone is regularly being hit by voltage spikes which will eventually damage the equipment as any in built voltage protection is under increased strain. This means that these phones are more prone to failure than designs which use a separate power supply.

No voltage on fibre lines

The bigger problem is the removal of voltage from phone lines as copper is replaced by fibre. Fibre cannot carry voltage. As the UK is currently experiencing a transition from copper to fibre lines, this problem becomes more acute.

As fibre is deployed and the line voltage is removed, line powered phones will cease to function.

Phone solutions

There are two main options to overcome the new challenges line powered phones face:

1. Replace the fibre line with a more resilient and futureproof GSM solution, such as the DCP
2. Add a dedicated power supply. However, it’s worth noting that once the phone has its own power supply, it also needs its own battery backup. As EN81-20 requires the backup power supply to be monitored, giving an alert if the battery fails or its charge drops below the 1-hour backup, it is important to ensure the setup is monitored and tested regularly, providing alerts when the battery and/or backup battery needs to be replaced.

Contact our team now for a free consultation on how to transition your analogue lift emergency phones to ensure compatibility with digital technologies.

Author: Milagros Gamero, EU Marketing Communications Manager at AVIRE