5. CABLE AND JACKPOINTS FOR STAR WIRING
Since 1988, commercial building cabling has been excluded from our Telepermit system on the grounds that commercial customers need the freedom to decide on how their premises should be cabled for their particular needs. Also, of course, commercial customers usually have the knowledge and resources to either specify their requirements themselves or call up the services of consultants and specialist contractors.
Telecom's primary requirements are that all hardware used for cabling connected to its network is "purpose-designed" for telecommunications and that the installation adequately supports Telecom services. The usual recommendation is to cable commercial premises in accordance with AS/NZS 3080 (which is basically the international standard ISO/IEC 11801).
The requirement for Telepermit has been retained for residential customers as a clear indication of what products are accepted by Telecom in respect of their reliability and suitability for purpose. Residential cabling can be carried out by the customers themselves and by non-specialist contractors, so it is important that some guidance is provided.
Jackpoints are a critical item as regards reliability - should a jackpoint fail, the customer's service usually also fails. With our relatively damp and marine climate, and typically colder homes (by overseas standards), jackpoint corrosion is a very common problem - mainly because there are around 4 million in service and even a very low failure rate results in thousands failing each year. Because of our operating environment and the large number in service, Telecom insists on Telepermitted 2-wire jackpoints having heavier protective plating on the contact springs, no exposed copper on the circuit boards, and protective coating over all of the internal components.
Even with star wiring, we still recommend standard 2-wire jackpoints for POTS applications, as they have proved more reliable than other types. Also, of course, they match the plugs used on the CPE.
Cable is a different matter. The type of cable used is not particularly critical for PSTN voiceband services, as long as it is well-designed and manufactured. For two-pair cable, we have set some minimum performance standards (Category 3 or better) and we still require this type of cable to be Telepermitted.
Now we are promoting the use of 4-pair cable to at least Category 5 performance for all new wiring, the position aligns more closely with that for commercial premises. Good quality cable is required under international standards to be clearly marked with its performance rating. Since Telepermit requirements are based on exactly the same standards, the most practicable approach is for Telecom to accept the use of any 4-pair cable which has already been certified. This is indicated by the appropriate markings on the cable sheath.
There is no doubt that future network services will make use of higher frequencies, so Telecom is now requiring that new 4-pair cable should meet at least Category 5. This is regarded as the current industry "norm" in any case. Any cable on which the sheath bears approval marks indicating Cat 5 or better performance is now acceptable for residential wiring.
While 2-pair cable is still acceptable if customers are certain that they only need "traditional" loop-wired jackpoints, it is recommended that star-wired 4-pair cable be used for all new installations.
Whichever type of cable is used, make sure the cable enters from below the jackpoint.
Based on the number of corroded jackpoints being replaced by Telecom each year, water entry into New Zealand homes is probably even more common than recent publicity about "Damp Homes" has suggested. Jackpoint corrosion only arises in damp conditions and one way water can get into the jackpoint is by running along and down a cable. This source of trouble is easily avoided by making sure the cable enters from below the jackpoint with the sheath end below the circuit board. Any water getting into the home and onto the cable then drips off the bottom of the loop and cannot run onto the jackpoint components to corrode them.
While it seems unlikely, it is not impossible for water to enter the PVC cable sheath, which is not totally impervious. This is why we require cable to be kept clear of the soil under buildings and not make contact with the bottom plate of exterior walls. If it does enter, the water can be transferred for quite long distances before it exits the sheath at the jackpoint. As long as the sheath end is below the circuit board, any water carried within the cable sheath cannot contact the board or its components.
These appear to be fairly minor details, but experience has shown that these are simple steps that can be taken to avoid completely disrupting a customer's service.
6. BILLING FOR TELEPERMIT PROCESSING
Many Telepermit applications are submitted by third parties, such as test laboratories, on behalf their clients. We have no objections to this process, as any service which helps the proposed Telepermit holder to get things right is also to our benefit. Sometimes, the applicant organisation will ask that we bill them. In other cases, we are asked to bill the nominated Telepermit holder. Our Telepermit application form has an entry for the applicant to state which party should be charged the actual Telepermit processing fee.
All parties concerned in making Telepermit applications are asked to make a firm decision as to who should be charged and indicate the party concerned on the application form.
It causes a considerable amount of difficulty for us if we have to arrange for our Accounts people to reverse an invoice to one party and charge another.
DOUG BURRUS
Manager
Access Standards
