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Telecommunications Network Equipment and Current NEBS Requirements
By Mark Render, EMC and Radio Group Manager, KTL
Introduction In order for manufacturers of telecommunications network equipment to gain access to the US market, it may be necessary to comply with “NEBS” requirements for EMC, product safety, and environmental performance. This is in addition to FCC requirements. The term “Nebs” is derived from Network Equipment Building Systems. Nebs testing is required by manufacturers who sell their equipment to the US Regional Bell Operating Companies (RBOCS) and include companies such as Bellsouth, SBC and Verizion or Competitive Local Exchange Carriers (CLEC). In addition suppliers to other US markets may also be asked if their equipment is Nebs compliant as many distributors are using these requirements as part of their procurement specifications.
What Standards apply to your Equipment? There are many standards that fall within the scope of Nebs. The standards most commonly used are as follows:
· GR-1089-CORE - Electromagnetic compatibility and electrical safety · GR-63-CORE - Physical protection
These standards are published by Telecordia (formerly Bellcore) and are often referred to as Bellcore standards. This article summarised the requirements
What are the Nebs Criteria levels and what tests are performed? NEBS compliance must meet one of three criteria which are defined in Special Report SR-3580, in order to satisfy all the intended applications of the equipment , and take into account the impact of a non-conformance. For each test level, the requirements are defined.
Special report SR-3580 provides further background and defines the Nebs criteria levels as follows:
Level 1 The minimum acceptable level of environmental compatibility needed to preclude hazards and degradation of the network facility and hazards to personnel. Level 1 products would include prototype equipment for trial and limited deployment equipment used for non vital services.
Level 2 The minimum acceptable level of environmental compatibility needed to provide limited assurance of equipment operability within the network facility environment. This assurance of operability is limited to controlled or normal environments. Level 2 products would include equipment deployed in controlled environments and equipment performing non critical network services.
Level 3 The minimum acceptable level of environmental compatibility needed to provide maximum assurance of equipment operability within the network facility environment. The level 3 criteria provide the highest degree of equipment operability. Level 3 products include critical network equipment such as digital switches and power systems.
SR-3580 states that all NEBS criteria are Important for efficient equipment deployment and reliable and safe operation, and as such, products should be designed to meet all the applicable requirements.
The following tables provides a brief summary of the types of tests performed for each criteria level:
It should be noted that each of the RBOCS and CLECs will specify the Nebs levels that are required. Additional test to the above may also be specified such as GR-487-CORE which covers generic requirements for electrical equipment cabinets. This includes all manor of extreme tests such as resistance to bullets and wind driven rain intrusion.
Depending on the market some tests may not be required for example compliance with the earthquake tests may not be required if the equipment is only to be installed outside an earthquake zone.
Requirements The ultimate determination to EMC and electrical safety generic criteria for network telecommunications equipment rests with the individual LECs. This section details Bellcore’s view of these criteria (classified as to their effect on equipment operation and reliability in the EMC environment) and of criteria intended to ensure the electrical safety of personnel. The following requirements terminology is used throughout the Telcordia standard:
· Requirement – Feature or function that, in Telcordia’s view, is necessary to satisfy the needs of a typical LEC. Failure to meet a requirement may cause application restrictions, results in improper functioning of the product, or hinder operations. A Requirement contains the words shall or must and is flagged by the letter “R”.
· Conditional Requirement – Feature or function that, in Telcordias view is necessary in specific LEC applications. If a LEC identifies a Conditional requirement as necessary, it shall be treated as a requirement for the application(s). Conditions that may cause the Conditional requirement to apply include, but are not limited to, certain LEC application environments, elements, or other requirements, etc. A conditional requirement is flagged by the letters “CR”.
· Objective – Feature or function that, in Telcordia’s view, is desirable and may be required by a LEC. An objective may be reclassified as a requirement at a specified data. An objective is flagged by the letter “O” and includes the words it is desirable or it is an objective.
· Conditional Objective – Feature or function that, in Telcordia’s view, is desirable in specific LEC applications and may be required by a LEC. It represents a goal to be achieved in the specified conditions(s). If a LEC identifies a Conditional Objective as necessary, it shall be treated as a requirement for the application(s). A Conditional Objective is flagged by the letters “CO”.
· Condition – The circumstances that, in Telcordia’s view, will cause a Conditional Requirement or Conditional Objective to apply. A Condition is flagged by the letters “Cn”.
New edition of GR-1089-CORE, Issue 3 October 2002 The latest version of GR-1089 contains extensive revisions. In summary these are;
Section 2: System Level Electrostatic Discharge (ESD) This section discusses the system level ESD and electrical fast transient requirements. The test method has been harmonised with the most recent revision of the international basic EMC standard for ESD, IEC 61000-4-2. Previous editions of GR-1089-CORE required that this test only be applied to EUT case. The new edition requires application of the test to telecommunication and power ports. The test methods are as specified by IEC 61000-4-4.
Section 3: Electromagnetic Interference This section covers electromagnetic emissions and immunity criteria for equipment located in telecommunications facilities and network equipment located at customer premises. This section contains significant differences from European standards, for example, the radiated electromagnetic field immunity test is specified over the frequency range of 10kHz to 10GHz; the European requirement being 80MHz to 2GHz. The test level depends on the criteria applied. Tests have been added to address the conducted emissions and immunity criteria at broadband frequencies.
The AC mains conducted emissions test has been modified to cover the new FCC requirements. In the frequency range 150kHz to 30MHz the limits are now identical to those specified by CISPR 22 based standards
Section 4. Lightening and AC Power Fault Resistibility This section discusses voltages and currents that may occur in telecommunications networks due to the effects of lightning and ac power faults.
Various editorial additions and modifications have been made to this section, the most significant of which are summarised below:
A conditional requirement and objective has been added to address the application of external current limiters in high speed digital networks.
A procedure has been defined for determining the proper voltages and currents to be applied to equipment containing secondary protectors during the lightening and AC power fault tests.
The procedure for current-limiting protector tests has been modified.
Section 7. Electrical Safety Criteria This section is concerned with the safety of personnel during normal use or maintenance or repair.
Where possible the terminology has been harmonised with international and North American telecommunications safety standards (harmonisation with UL60950 with respect to definition of test fingers).
Section 9. Bonding and Grounding. This section describes the requirements for bonding and grounding systems. The modifications to this section provide clarification on test procedures and clarifies the number of samples required to be tested in each section.
Guidance has also been provided on the application of the criteria to various types of network equipment. Further clarification has also been provided on compliance criteria relating to the short circuit tests.
Conclusion The latest version of GR-1089-CORE contains significant differences to previous versions which are outlined above. Careful review of the requirements is recommended before NEBS requirements are considered. It should also be noted that RBOCS and CLECS would normally specify the level they require for testing, and manufacturers would than approach a test laboratory to have the testing performed. RBOCS also have different acceptance criteria, such as the testing being performed by a Nationally Recognised Test Laboratory (NRTL).
Mark Render can be contacted by phone on +44 (0)1482 801801 or Email: mrender@ktl.com
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