Anyone working with ABS and USCG rules will know that more and more IEC (International Electrotechnical Commission) International Standards are acceptable alternatives to NEMA and IEEE standards. The IEC standard applicable to marine systems is IEC 60092 Electrical installations in ships. This standard has multiple parts encompassing everything from system design, equipment and cables to electrical propulsion plant, tankers and control and instrumentation systems.
Part 505 which deals with Mobile Offshore Drilling Units is presently being re-written and will be published as IEC 61892 Mobile & fixed offshore units—Electrical installations. When complete, this standard will be in 7 parts. Presently parts 3, 6 and 7 covering Equipment (3), Installation (6) and Hazardous Areas (7) are published. Electronic equipment is covered under several publications including IEC 60872-2, 61993-1 & 60936-2 Maritime navigation & radio communication equipment & systems. A recent publication—IEC 61363-1 will be of interest to electrical marine consultants. The standard provides detailed Procedures for calculating short-circuit currents in three-phase ac marine electrical systems.
The IEC committee responsible for IEC 60092 Electrical installations in ships
meets every two years. In 1998 the committee met in Houston at the new impressive conference center and was chaired for the last time by Mr. Colin Porter of Lloyd’s Register of Shipping. The year 2000 meeting has unfortunately been cancelled and the next meeting will be held in Italy under the chairmanship of Dott Ing Giovanni Rebaudengo who recently retired from Registro Italiano the Italian classification society.
Of the many issues discussed in Houston, work was completed on storage batteries, high-speed craft and pleasure craft installations. Of significance to marine electrical system design was the introduction by SOLAS and adoption by IEC of a requirement to maintain or immediately restore power to essential services following a failure of a main generator. This requirement is designed to protect generators by load shedding non-essential services. The other significant change was the requirement to install a circuit breaker or “other approved means” to subdivide the main distribution bus at the ship’s main service switchboard. This requirement is already a part of the US Code of Federal Regulations.
As is always in IEC the interpretation of the wording of the requirements caused considerable discussion. With regards to the above regulations, the words “immediately” and “other approved means” required explanation. It was finally agreed that “immediately” could be achieved by restoring power within 45 seconds. “Other approved means” may include a disconnect, switch or other similar devices by which the bus-bars can be readily split without the use of specific tools. The use of bolted bus links, as has been applied many times in the past, is no longer allowed.