Harmonized Part 68 Surge Requirements

Type A Surges

Type B Surges

Applicability of both Surges

Do I absolutely have to perform Type B surges?

Do I have to perform all of the network protection tests after the Type B surges?

CCL Services

Other areas that have changed in Part 68

HARMONIZED FCC PART 68 ISSUES

New FCC Part 68 Harmonized Rule Effective Date

On April 20, 1998, the FCC Harmonized Part 68 Requirements became effective. This date is based on the deadline specified in the Harmonized Report and Order, which is 150 days after the publication date of the Order in the Federal Register on November 19, 1997. Subsequent to the effective date, due to the fact that the Order as well as the Federal Register documents contained various technical errors, the Commission suspended the enforcement of the Harmonized Rules for 30 days, beginning on May 7, 1998, until June 8, 1998. During the period of time between April 20 and June 8, 1998, the FCC is accepting Part 68 applications with compliance data according to either the old Part 68 version or the new Harmonized Part 68 version. The suspension was granted based on industry’s request, as put forth by the TIA delegation to the FCC on April 23, 1998, with the reason that technical errors were not corrected in time for the April 20 deadline. CCL’s Director of Engineering Anh Wride was part of the TIA delegation in her capacity of Chair of TIA TR41.9 Committee.

Harmonized Part 68 Surge Requirements

The FCC Part 68 Harmonized Requirements contains two types of surge requirements, both MANDATORY, the Type A and the Type B surges on the telephone interface, both metallic and longitudinal.

Type A Surges

The Type A surges are identical to the old Part 68 surge requirements, however, the open circuit voltage and short circuit current waveforms are better defined. For years, the language in the old Part 68 was unclear regarding the decay time of the open circuit voltage and the short circuit current waveforms. The Harmonized Part 68 requirements for Type A surges were reworded for clarity, and specify that both the short circuit current and the open circuit voltage waveforms must comply with the MINIMUM specified decay time. This does not mean that the current and voltage waveforms must meet exactly the same timing (an impossibility!). Due to phase lag, the timing for the voltage waveform is normally longer than the current waveform; if the short circuit current waveform complies with the MINIMUM specified decay time, then the open circuit voltage waveform would also comply. The key in the requirements is the MINIMUM timing requirements, which mean that anything being "at least as long" or "longer than" the specified timing will be considered to be compliant. The fail-safe criteria for the Terminal Equipment after the application of the Type A surges remain unchanged: the Equipment may remain permanently disabled following the opening of a component in the interface (i.e., fuses, etc.) and would still be considered to be compliant with the Rules.

Type B Surges

The Type B surges are new. This new type of surge is based on the ITU Recommendation K21. The surge is well defined in terms of open circuit voltage and short circuit current waveforms and an idealized circuit is provided within Part 68, Section 68.302. Since the Type B surges contain much lower energy than the Type A surges, the fail-safe criteria for the Terminal Equipment was redefined: the Terminal Equipment must demonstrate that its interface circuitry retains its integrity (no open component, etc.) such that the equipment can continue to go on-hook and off hook, for example, in the case of a telephone set. In circuits such as E&M tie trunks, or digital T1 or subrate, since the interface circuit does not provide an on-hook and off-hook state per se, the interface must be scrutinized for open components causing the path to the central office to be incomplete or inoperative. Despite this new fail-safe criteria, the Terminal Equipment is not required to be functional after the Type B surges, as far as telephony features are concerned, such as data transmission, DTMF dialing, etc. The reality is that if the interface circuit can still function and can provide a complete path to the network, data transmission circuitry as well as DTMF circuitry, which are situated well behind the coupling transformer and other barriers, will most likely continue to function.

Applicability of both surges

Both surges are MANDATORY. The Type B surges are specified to be applied after the first set of network protection tests. The Terminal Equipment is then evaluated for interface circuitry integrity (is there still a path through the interface?) and then a complete second set of network protection tests are administered. The Type A surges, including the power supply surge (which has not been changed by harmonization), are then performed on the Terminal Equipment, after which, it is permissible for the interface circuit to remain disabled, i.e. permanently on-hook, or presenting no path to the central office. The last set of network protection tests is then performed, depending on the applicable states of the Terminal Equipment (i.e., if the Equipment remains permanently on-hook, then only on-hook tests will be required to be conducted).

The surge was the most contentious area during the Harmonization process. The adopted requirements represent a hard-won industry consensus. Knowing the confusion that would undoubtedly reign after the effective date of the Harmonized Requirements, TIA TR41.9 Committee has issued a revision to the much acclaimed TSB31 document, Part 68 Rationale and Measurement Guidelines. This document contains a flowchart outlining the order of the testing, and may be purchased via Global Engineering at 303-397-7976.

Do I absolutely have to perform Type B surges?

There is an erroneous assumption that if the Terminal Equipment under test continues to be completely functional (all telephony features are operational) after the Type A surges, that there is no need to do Type B surges. This assumption may be valid for manufacturers who are well acquainted with the design of their interface circuit and have geared the design and construction of the equipment toward complete survivability after the Type A surges. Even so, supporting data and design attestation are necessary if such an assumption is used, to provide assurance that the equipment has indeed been designed for complete survivability, and the fact that it survived the higher energy Type A surges is not a "fluke" that just happened to the sample under test. For test facilities who perform testing on various types of equipment for various types of manufacturers, vendors, etc., and have to contend with sample limitations (most of the time, (1) engineering prototype sample), as well as lack of knowledge on the actual design objectives of the equipment, both surges must be performed. As Type B surges are required to be performed before the Type A surges, there is no choice but to perform both types of surges according to the order as recommended in the TIA TSB31B Guidelines.

Do I have to perform all of the network protection tests after the Type B surges?

It is obvious that the Type B surges and the new fail-safe criteria associated with this type of surge is adding another tier of testing to the Part 68 compliance.

It is however intended for complete testing of all network protection characteristics to be performed before any surges, after the Type B surges and then after the Type A surges.

If no testing or limited testing were to be specified to be performed after the Type B surges, and the same equipment remains permanently on-hook after the Type A surges, the areas that were not tested may have yielded a failure to comply with the criteria of Part 68. However, because no testing or very limited testing was performed, the failure areas were not uncovered, and were subsequently masked by the opening of a fusible component after the Type A surges.

If the equipment is subsequently tested (for example, in a future modification application) by a different testing facility (or different test personnel) who does perform complete testing after the Type B surges, failures may surface and will cause problems and create headaches to the designer, as there will be no way of knowing whether the original design was actually non-compliant, but testing was not performed therefore this was not revealed, or the modifications done to the equipment, now, in the modification filing, were themselves non-compliant, etc..

In order to retain repeatability and uniformity in Part 68 testing among test facilities, including manufacturer test labs and independent test labs, the TIA TR41.9 Committee unanimously recommended that COMPLETE TESTING be performed before any surges, after Type B surges, and after Type A surges. The Committee did however retain the notion of Engineering Evaluation as allowed in the TIA TSB31B document.

CCL can help you with the Harmonized Part 68

CCL, (Communication Certification Laboratory), an industry leader in Part 68 testing, can help our clients perform the Harmonized Part 68 surges on their Terminal Equipment. CCL uses a commercial modular surge generator containing surge modules that conform to the Harmonized Part 68 Type A and Type B surges requirements, as well as the Power line Surge requirements. Complete Part 68 testing including submission of the application to the FCC is available as well as partial testing, for our clients who desire to test their current circuit design against the new Type B surge for determination of survivability. Contact either Rich Winter (rlw@cclab.com) or Joe Jackson (jwj@cclab.com) for details.

Comparison of FCC Part 68 Surges and Canada CS-03 Surges

The surge was one of the few areas where complete harmonization was not able to be achieved. The Canadian CS-03 requirements only include Type A surges, both on the telephone interface circuit and on the power supply circuit of the Terminal Equipment. In this respect, the CS-03 surge requirements are identical to the FCC Part 68 Harmonized requirements for the Type A surges, including the fail-safe criteria associated with this type of surge. CS-03 Standard does not provide requirements for the Type B surges.

Other areas that have changed in FCC Part 68 Harmonized Requirements

Keep a look-out for a list and description of the other areas of FCC Part 68 that have changed due to Harmonization here.