Ring Equivalent Number & ADSL Filters Explained

The Landline Telephone Part 2

Well as we all know its not just about speech any more, most homes & work places now use the telephone line for more than just making calls. Generally speaking some of the most common integrated uses of telephone lines in a domestic setting are that of the Digital Subscriber Line technology for broadband internet access, alarm monitoring communications, fax machine use, modems & interactive communications inclusive of device management / monitoring.

All in all there's a lot of stuff available via the Public Switched Telephone Network service line, provided that all attached devices are installed & configured on technically correct customer side wiring.

Lets take a brief look into this; its not unheard of now a days for domestic households to have the following items on just one telephone line.

• Broadband services

• Telephone device

• Alarm monitoring connection

• Other devices – (Fax machine/skybox/etc.)

Based on a technical limitation called the Ring Equivalent Number of a standard telephone line, this would typically be the limit of ringing devices one could expect to have working without experiencing service or equipment failure.

Most devices available for use on a standard telephone line will have a reference label attached indicating REN value, typically 1 or 0.5. The total number of REN should not exceed 4, maintaining this basic condition is one simple step that can be taken to ensure trouble free communications.

Remember that you should always ensure that your internal wiring is in good condiytion and meets a minimum standard of CW1308, in the event that your cable runs outside it should be of an external grade standard such as CW1128.

NTE 5 Master Telephone Socket & Extra Telephone Socket Extension Points

  

Although very simplified in the above diagram, its clear to see that all devices connected to the line on a broadband enable line should be filtered. This will minimise cross interference to & from the voice & data sides of the service. On that note it is worth while mentioning that one of the most common types of failure in this type of configuration, is that of a faulty filter. As such it is good practice to have one or two good quality spare filters to hand especially when they cost less than £5.

Independent telephone engineer Bury Lancashire & Greater Manchester