TELECOM ACCESS STANDARDS NEWSLETTER NO. 78 JANUARY/FEBRUARY 1995 CONTENTS 1. TELECOM WIRING STANDARDS 2. REMOTE POWER METERING: WIRING SAFETY ISSUES 3. NEW GENERIC BUILDING CABLING STANDARD AS/NZS 3080 DUE SOON 4. TELEPHONY STANDARDS: PTC 202, ISSUE 2 DRAFT 5. PABX TOLL BARRING AND NUMBER LENGTH CAPACITY 6. TELEPERMIT STATISTICS 7. DATA TRANSMISSION VIA THE TELECOM CELLULAR NETWORK RETURN TO MAIN INDEX 1. TELECOM WIRING STANDARDS It has been reported that there is a growing trend towards the use of non-standard wiring practices, especially in residential and small business installations. Usually, problems occur where the work has been carried out by persons who do not appreciate that there are valid reasons behind Telecom's practices. PTC 103 was issued in 1987 to define Telecom's standard wiring practices in the form of a public document. At that time, the aim was to gradually bring earlier installations into line with our standard jackpoint practice and avoid mixed installations with earlier jack systems and fixed terminal blocks. Because of the usual competitive pressures to reduce costs, this original objective has not always been followed in older homes and we have ended up with many of these mixed systems. Nevertheless, our residential customers now own the wiring in their homes and it is not for us to insist on them converting all older Post Office or Telecom installed wiring to the current standard. New wiring is another matter. As a contractual requirement on our customers (Section 3 of the new "Standard Terms for Residential Customers" is a readily available reference), all wiring must be installed according to Telecom' s specifications. In essence, there are two separate wiring systems in use; the 3-pair 0.4 mm wiring used with BT sockets in residential and general business installations, and the 4-pair 0.5 mm wiring used with 8-way modular sockets in modern generic cabling systems. These are installed mainly in the more recent large commercial installations. These systems both include standard colour code allocations for the wire terminations. Both systems also use Insulation Displacement Connectors (IDC) for terminating the wiring on the sockets. These avoid the need to strip insulation from the conductors and provide a simple form of termination. However, joint reliability is very dependent on whether the manufacturer's recommendations have been correctly followed. For the Krone IDC connector used in our jackpoints, the manufacturer specifies that not more than two solid conductors of the same gauge are inserted in a single connector slot, using the correct insertion tool. Mixed gauges can lead to joint failure because the larger wire reduces the contact pressure on the smaller wire. While joints appear satisfactory when installed, the risk of subsequent failure is greatly increased. Similar problems can occur with stranded wire, which simply "spreads out" to better fit the IDC slot, resulting in insufficient contact pressure. Telecom maintains virtually all residential wiring installations and a very large percentage of small business wiring installations under its 50 cents per month Wiring Maintenance Service. Our maintenance staff recognise these standard wiring systems as Telecom-related and have the tools and replacement hardware to maintain them. However, should the installer have used other than the standard type of cable, there is the problem of identifying the cable itself and the possibility that different gauges will be inserted in the same IDC slot. Non-standard colour coding is a further source of delay and confusion for the serviceperson. SPECIAL NOTE: The use of power cable for telecommunications wiring connected to the Telecom network is absolutely forbidden on the grounds of electrical safety. This rule exists to ensure that our staff can always differentiate between telecommunications wiring and power cable at potentially hazardous voltages. Other types of cable, such as flat alarm cabling and stranded cable commonly used for extra low voltage (ELV) wiring are also forbidden because of the identification and reliability problems. Obviously, cases arise where an installer was on site to provide a particular service to the customer and simply added some telephone sockets with the same cable while he was on the job. This probably provided a "cheap solution" for the customer at the time. However, under the terms of its contract with the customer, Telecom is ONLY required to accept responsibility for wiring which was done in accordance with its practices and may charge the customer concerned for subsequent remedial action. Non-standard work is thus obviously NOT totally fit for its intended purpose, even though it may appear to work when first installed. Any trades people carrying out such work should be aware that they are risking claims against them under the Fair Trading or Consumer Guarantees Acts. 2. REMOTE POWER METERING: WIRING SAFETY ISSUES a. Regulatory aspects Recent weeks have seen requests to have Telecom jackpoints installed in the rear of 230 V switchboards and meter cabinets. In some cases, this work has been carried out by electricians, who are qualified to work within these enclosures. Such wiring is NOT covered by our Wiring Maintenance service. In any case, the Electricity Regulations do NOT permit most Telecom field staff to work within power switchboards and meter cabinets. While we have not required strict adherence to jackpoints and 3-pair, 0.4 mm conductor cable in older installations, we DO insist that ALL installations meet our safety requirements and that they comply fully with the Electricity Regulations 1993 and any subsequent Amendments to these Regulations. Our complete prohibition of the use of power cable for telephone services is one example of such a safety requirement, as mentioned above. In terms of the Electricity Regulations 1993, telecommunications cabling is essentially in the "Extra Low Voltage" (ELV) class. Strictly, it operates at "Telecommunications Network Voltage" (TNV), a special class of ELV under the Regulations. It is separately defined in AS/NZS 3260 (IEC 950) to cover the presence of ringing voltages. Nevertheless, the Electricity Regulations require the segregation of ELV and TNV cabling from 230 V (Low Voltage) cabling. (ref. NZECP 7, clause 7.16.1 and clause 1.11 of Appendix A ; and NZECP 28, clause 4.8). As stated in clause 6.5 of PTC 103 in relation to wiring connected to Telecom's network:- "Telecommunications cables shall not run through electric power distribution boards under any circumstances". Work within 230 V switchboards is deemed to be prescribed electrical work under Electricity Regulation 16 (1). The exemptions for TNV wiring under the two sub clauses of Reg. 16 (2) (l) do NOT extend to work on TNV wiring within 230 V switchboards. Where power supply companies wish to install remote metering or power usage monitoring equipment, care is to be taken to comply with accepted safety practices in terms of both segregation of cabling and isolation of mains voltages from the Telecom network. The basic principles are that only an electrician or other person authorised to fit load control and revenue meter equipment may install the monitoring transducer and wiring within a meter cabinet. This wiring must be run in 300 V rated cable. Telecom requires assurance that there is full isolation between the mains and the telephone wiring (typically, at least 1500 V in accordance with AS/NZS 3260) and that there be a clear point of demarcation. Provision should also be made for the meter wiring to be easily disconnected from the telephone wiring for fault location purposes. Isolation may be supplied by the transducer or by the modem which finally passes the processed meter information to the phone line. The modem itself is subject to PTC specifications and shall have been granted a Telepermit. b. Interim solutions Power supply companies would no doubt prefer to install all their hardware in the meter cabinet, where it can be powered from their side of the meter. While they may also wish to connect direct to a Telecom jackpoint installed in the meter cabinet, there are the problems of compliance with the Electricity Regulations and the inability of Telecom staff to maintain the jackpoint, as explained above. There is also a practical issue where the meter cabinet is mounted on the outside of the building, because a Telecom jackpoint is not designed for such applications. It provides only short creepage and clearance paths, is subject to continuous 50 V d.c. and its long term reliability is doubtful if it is subjected to dampness, dust, and wide variations in temperature. These are the sort of conditions that could apply in an outside meter box. The hardware used within a meter cabinet is mainly a matter for the power supply companies to determine where they are undertaking any servicing. However, we do not want to have a situation where problems within the power wiring affect the customer's normal telephone service. A key point is that a clear demarcation point should be provided outside the meter box, but inside the building, at which Telecom can rely on the connection to its network being adequately isolated from mains voltage. A plug-connected interface could be provided for future fault location and servicing. For example, a RJ 11 6-way socket with screw terminals for the heavier cable, could be sited next to a standard Telecom jackpoint. A short cord with a BT plug on one end and an RJ plug on the other could then be used as the interconnection. In the event of service problems, the meter wiring can then be easily disconnected and reconnected during testing. This arrangement would meet the basic safety aspects of the Special Note in item 1 above. The attached sketches show typical layouts that are expected to meet Telecom's requirements. No doubt other acceptable options and more suitable hardware can be developed once we are aware of a specific power supply company's requirements. To help ensure that safety requirements are fully complied with, Telecom is currently considering the publication of some form of "acceptable practices handbook or brochure" for this class of work. It is expected that this will be developed in conjunction with representatives from the various power supply companies. In the meantime, enquiries relating to such installations and their connection to the Telecom network should be addressed to Access Standards. We will liaise with our field management to ensure that suitable safe practices are established for all such installations. 3. NEW GENERIC BUILDING CABLING STANDARD DUE SOON Standards New Zealand and Standards Australia expect to be publishing the new Joint Standard AS/NZS 3080: 1995 about mid-year. This standard, "Telecommunications Installations - Integrated Telecommunications Cabling Systems for Commercial Premises" applies to commercial building telecommunications (data, telephony, LAN's, WAN's, etc) services. A Joint Working Group of Australian and New Zealand representatives has been working on the new standard for over a year, keeping up with the latest American and International industry developments. While the title of the new Standard includes the word "Integrated", as did the earlier Australian version, the essential issue is that the cabling systems dealt with are "generic". In other words, they are application independent and designed to provide sufficient flexibility to handle a wide range of current and future applications The current 1992 version of AS 3080 is based on the 1991 edition of the North American standard, EIA /TIA 568, with various Australian additions to cover their practices and regulatory situation. The forthcoming AS/NZS 3080: 1995 is being based on the international "derivative" of the latest draft version of EIA /TIA 568, which is also to be published soon as ISO/IEC 11801. Standards New Zealand are planning to run some low cost introductory seminars in the main centres coincident with the release of the new Standard. The exact timing is still not firm, but those interested in cabling matters are encouraged to look out for further announcements. The allocation by architects and building owners of sufficient space for building cabling and its associated equipment has been a frequent problem for Telecom and other installers. Another Standard worthy of reference by those involved in building design is AS 3084: 1993, "Telecommunications Installations - Telecommunications Pathways and Spaces for Commercial Buildings". This Standard outlines the needs for properly designed cable access, cross connect frame accommodation, etc. Obviously, it is cheaper and easier to design these into the building, than to end up with the need to cut holes and provide access when the building has been completed. From Telecom's viewpoint, the more widespread the use of the various industry and national Standards, the better we will be able to support our customers' service requirements. 4. TELEPHONY STANDARDS: PTC 202, ISSUE 2 DRAFT The "Draft for Public Comment" of Issue 2 of PTC 202 was published just before Christmas. This document does not deal solely with telephone instruments. It also covers many other forms of telephony devices, whether they incorporate electro-acoustic or stored message type functions. In its new loose leaf format, we are able to add or amend complete sections as and when required. We are considering the possibility of gradually incorporating other intended and current PTC specifications into it, especially where there is a high degree of commonality in Telepermit requirements. For example, we expect to publish another section dealing specifically with cordless telephones in the near future. The draft is available on order from Access Standards at a charge of $90, inclusive of GST and postage. As usual, those purchasing the draft will be sent a copy of the "final" version at no extra cost. Free supply also applies to any additional sections of the specification that may be added before Issue 2 is formally published. Readers should note that this new loose leaf A4 format version is normally provided without the binder. If required, we can provide binders as an optional extra at a price of $12, inclusive of GST and postage. These A4 binders will have the Telecom logo and title and will be suitable for holding several PTC specifications when they are converted to A4 format. 5. PABX TOLL BARRING AND NUMBER LENGTH CAPACITY A minor correction regarding answer signal timing for Telecom Calling Card calls in that an answer signal is given after the network receives the called number just prior to the first voice response thanking the caller for using the Telecom Calling Card Service. This does not impact on the basic intent of the article, which was to raise the issue of growing number lengths and the need for PABX systems to be able to cope with even longer number lengths after December 31 1996. 6. TELEPERMIT STATISTICS As mentioned in the December Newsletter, this year was looked to be heading for a record early on. It certainly made it as, by year's end, we had granted a total of 511 Telepermits (plus 63 new Limited Permits, which generally convert to full Telepermit late) . The previous "record year" was 1991, when we granted 406 Telepermits. The PTC 211 non-voice product group (mainly modems and fax machines) reached a record 210 for the year. It was also interesting to note that cordless telephones outstripped conventional wired phones 21 to 12 - either the economy really is improving, or our customers' requirements are increasing. No doubt Telecom's withdrawal from much of the CPE market has brought a burst of optimism from other suppliers. ISDN is another area which looks as if it is about to take off after a slow start, with 28 new basic rate CPE products Telepermitted last year. This product group almost caught up to Telecom's AMPS cellphones, 30 types of which were Telepermitted. Those readers wanting full details can refer to the Telepermit Register, which is available at $15 per copy or at $50 for an annual subscription covering four quarterly issues. These prices include GST and postage. 7. DATA TRANSMISSION VIA THE TELECOM CELLULAR NETWORK AMPS cellphones used on the Telecom Cellular network are subject to Telepermit, but there has been a long-standing problem with the connection of modems because there is no standardised interface between cellphones and modems. Each supplier tends to provide some sort of proprietary interface and it is not the same as that used for the PSTN network interface. Cellphone users needing data capability have generally approached their cellphone supplier for suitable hardware, but there has been no commonly available product information that covers the whole field of cellphone/modem interoperability to guide an intending purchaser. Modems Telepermitted for connection to the PSTN (PTC 211- series) may or may not be always suitable for cellular use. Common operating situations like cellphone handover can lead to temporary loss of carrier for tens of milliseconds and PSTN modems may release the call in such circumstances. As a means of overcoming this compatibility problem in a managed fashion, Telecom Cellular have introduced "DataLink". This is an initially informal accreditation system to "certify" and register those combinations of cellphone, modem and interface hardware which have been confirmed to operate correctly under cellular conditions. Telecom Mobile's cellular division will be inviting modem suppliers to learn more about this accreditation system shortly. In the meantime, those suppliers wishing to register their interest should make contact with Telecom Mobile by telephone on 0800 739 000. DOUG BURRUS Manager Access Standards