GR-1089 HDSL A3 V OLTAGE T ECHNICAL B RIEF HDSL is a powerful, cost-effective, T1-based transport technology that leverages existing copper infrastructure and is, therefore, of great interest to both subscribers and service providers. It uses central office (CO) units at the carrier's office and remote units at the customer site and may, depending upon distance, require HDSL repeaters over the length of the copper span. The power needed to operate the repeaters and remote equipment is provided over the span itself, and must be handled safely for the protection of users and telephone company craftspersons. Nobody cares more about the safety of telecommunications equipment than ADC Telecommunications, but when it comes to setting safety standards, the industry turns to Bellcore. GR-1089 is a detailed Bellcore specification covering, among other things, safe powering of facilities. Section 7 of the document defines levels of allowable electrical currents and voltages which may be applied to circuits and equipment, depending on who will have access to the equipment. • Class A1 is the most stringent and applies to areas which may be contacted by the general public, which is assumed to be unfamiliar with electrical hazards. • Class A2 permits higher limits and covers those areas where non-specialized telephone company employees may have contact. • Class A3 is the highest allowable level for voltages which may be contacted barehanded. It applies to those areas available only to telephone company craftspersons familiar with the appropriate precautions, and applies to HDSL circuits and equipment. Introduction Setting Standards 24/98 2 436 GR-1089 HDSL A3 Voltage Technical Brief The A3 standard covers both DC and AC voltages; however, only DC applies to HDSL equipment. According to section 7.2.1 of the GR-1089 standard, the limits apply “be- tween each terminal and ground with all other terminals first open-circuited, and then with all other terminals individually grounded.” “Terminal” refers to any HDSL wire pair. “Grounded” terminals are in contact with any conductor — a metal case, for example — with which a craftsperson could come in contact. This standard is designed to protect craftspersons both against electrical flows in individual circuits and against combined voltages in the event that one set of terminals becomes accidentally grounded, for example by having insulation pinched in the door of an enclosure. The risk at these levels is not just electrocution. It is the muscle spasms caused by the current flow, which can cause pulled backs, falls, or other dangerous accidents. The A3 standard, in section 7.2.1.3, sets limits on both voltage and current. At 140V or less, there is no limit on current. Between 140V and 200V, current may not exceed 10mA. In no event may voltage exceed 200V. All of these voltages are measured with respect to ground. (See graph) A3 Defined I dc (mA) 0246810121416 200 175 150 125 100 75 50 25 0 VDC (v) (10mA, 200V) (10mA, 140V) DC ONLY UNACCEPTABLE ACCEPTABLE These are simply standards and do not have the force of law. They are, however, the best available guidelines for protection of personnel who come in contact with equipment. Since manufacturers are not required to follow them, it is up to concerned buyers to check for compliance. Some confusing references to the GR-1089 standard have been made recently in the marketplace. Some of these appear to be worded specifically to mislead, and have gone so far as to imply — without actually stating so — that one vendor’s approach to HDSL powering is the only one compliant with GR-1089. 3 4/98 3 436 GR-1089 HDSL A3 Voltage Technical Brief There are two ways to meet GR-1089’s A3 standard for voltages under 140V. One is to provide a single compliant voltage, for example -130V. The other is to provide two separate, compliant voltages, one at -130V, the other at +130V, providing twice the voltage for powering the HDSL span. The +/-130V technique has been used to power long T1 spans since the 1960s, and has a excellent record for safety. Bellcore’s standard specifically tests for the safety of this approach (by requiring that each terminal be tested “ .with all other terminals individually grounded.”) The requirement for testing with “terminals individually grounded” simulates accidental grounding of a circuit within the span or equipment. Compliance with this requirement ensures that, even with twice the available voltage to the line and equipment, the 140V limit cannot be exceeded, even through accidental grounding. This allows craftspersons to handle the equipment with no more risk than if only a single voltage were present. The problem with the first approach — a single voltage at -130V — is that, while it is safe, it greatly limits the distance over which HDSL can be provided. 130 volts is only capable of powering a single repeater and the remote equipment. The second approach — two separate sources at +/-130V — allows support of remote equipment and two repeaters, increasing the maximum span length by 50 percent. As long as it meets the “terminals individually grounded” test, it does so with no sacrifice in safety. ADC’s HDSL terminal equipment uses this second approach. The long history of safe use of +/-130V for powering longer T1 spans was instrumental in the company’s decision. All the Safety With Twice the Voltage ADC equipment is carefully designed to meet Bellcore’s requirement for testing each terminal with the other “terminals individually grounded” and, in doing so, provides full protection to personnel as well as increased electrical potential to power longer spans. This is achieved in the design of the connection between the power supply center tap and ground. The connection is specifically engineered with sufficiently low imped- ance that grounding any tip or ring terminal will cause that power supply output to go into protective shutdown. This allows the system to power two repeaters per span, fully complies with the Bellcore GR-1089 requirements, and protects craftspersons working with the equipment. How it’s Done In Summary •Despite any suggestions to the contrary, the Bellcore GR-1089 specification has no preference for -130V over +/-130V span powering, as long as the requirement for testing with “terminals individually grounded” is met. •Any service which can be provided under -130V power without powering down the local loop can be similarly provided under compliant +/-130V power. •Despite suggestions to the contrary, you don’t have to sacrifice longer HDSL span-length to achieve full safety for your field personnel. •For your own protection and that of your personnel, you should ascertain that your HDSL equipment meets GR-1089 specifications. Not all equipment being sold today does. Include compliance in your specifications and be prepared to test, if necessary. ADC is committed to performance and safety in everything we sell. We will never sacrifice safety, but we believe that, through superior engineering, we can provide our customers with both. 436 4/98 Revision © 1997, 1998 ADC Telecommunications, Inc. All Rights Reserved An Equal Opportunity Employer Specifications published here are current as of the date of publication of this document. Because we are continuously improving our products, ADC reserves the right to change specifications without prior notice. At any time, you may verify product specifications by contacting our headquarters office in Minneapolis. ADC Telecommunications, Inc. views its patent portfolio as an important corporate asset and vigorously enforces its patents. Products or features contained herein may be covered by one or more U.S. or foreign patents. ADC Telecommunications, Inc. P.O. Box 1101 Minneapolis, Minnesota 55440-1101 FAX: +1(612) 946-3292 From North America, Call Toll Free: 1-800-366-3891, ext. 3223 Outside of North America: +1(612) 938-8080 Home Page Address: http://www.adc.com International Sales Offices: Belgium 32-2-712-6500 • United Kingdom 44-11-89-879- 200 • Montreal, Quebec (514) 677-9166 • Vancouver, BC (604) 270-1675 • Toronto, Ont. (905) 629-3104 • Ottawa, Ont. (613) 599-5729 • Singapore 65-225-8228 •Venezuela 58- 2-286-1444 • Mexico City, Mexico 525-658-4519 • Buenos Aires, Argentina (541) 788- 8700 • Sao Paulo, Brasil 55-11-3040-0666 • Sydney, Australia 61-2-9975-1499 • Beijing, China 86-10-6500-7001 • Dusseldorf, Germany 49-211-530-6550 • Seoul, Korea 82-2-333-8989 . to HDSL powering is the only one compliant with GR-1089. 3 4/98 3 436 GR-1089 HDSL A3 Voltage Technical Brief There are two ways to meet GR-1089 s A3. precautions, and applies to HDSL circuits and equipment. Introduction Setting Standards 24/98 2 436 GR-1089 HDSL A3 Voltage Technical Brief The A3 standard covers