Testing of standby generators without class attendance

Many ship operators do not seem to be familiar with our rule requirement updates released in June 2018. Since then, the ship’s crew has been allowed to conduct the annually required class test of the standby generator functionality without class attendance. Ship operators thereby benefit from increased flexibility. This technical news summarizes the improved test procedures

Technical Regulatory News 22 - control room

Relevant for ship owners and managers.

Background and necessity of the requirements

The rules for annual surveys (Pt. 7, Ch. 1, Sec. 2 [3.1.5]) specify that “For all E0, AUT or AUT-nh vessels (built at any time) and all vessels constructed on or after 1998-07-01 where electricity is necessary for propulsion and steering, test of the automatic start and connection to the switchboard of the standby generator set shall be carried out.”

Where the vessel’s normal seagoing load is covered by a single generator, this test shall be conducted by shutting down the running generator, i.e. creating a blackout. For vessels where the normal seagoing load is covered by two or more generators, the test shall be conducted by shutting down one of the running generators.

Long-term experience shows that restarting the machinery plant after a blackout is often problematic. This may be caused, for instance, by incorrect system settings, crew unfamiliarity, empty or faulty UPS units or, not least, empty internal batteries on chipboards or PLCs.

The only way to discover these issues, to ensure that the vessel can restore power after a blackout and avoid even more dangerous situations, is by testing the systems. This test must therefore be carried out, and, importantly, it must be carried out correctly. Simulating a blackout, i.e. triggering the standby generator to come on line without shutting down the single generator as required, will not reveal all hidden failures.

Testing difficulties

For various reasons, it is often difficult to conduct the test as required: oil/gas terminals do not allow vessels to immobilize, cargo operations are disrupted, the crew is afraid of damaging electronic equipment, etc. Whilst many of these challenges can be overcome through good planning and preventive measures such as shutting down non-critical equipment, this testing requirement still inconveniences the vessel.

New procedure for annual testing

To minimize the impact of the annual testing, class attendance during the standby functionality test is no longer required. This allows for the test to be conducted at a more suitable time.

If conducted less than three months before the annual survey, the test may be accepted during the annual survey. The test shall be conducted according to a written procedure which, for ships where the normal seagoing load is covered by a single generator, shall include a blackout.

In general, the procedure shall address the relevant items listed in the Appendix under Annex I: Guidelines for standby functionality test procedure. This procedure does not require class approval but should be presented to the attending surveyor for his/her acceptance.

The successful test shall be documented by a log book entry, a signed statement by the Chief Engineer and a copy or screenshot of the alarm log. If the test has not been conducted by the vessel at the time of the annual survey, or the operator simply wishes to conduct the test during the annual survey, this is still possible.

The test shall always be witnessed by class during renewal surveys on all vessels and during annual surveys for vessels where a poor condition and/or poor maintenance is registered.


In short, the testing of the generator standby functionality, sometimes referred to as the “blackout test”, is no longer required to be carried out during the annual survey. The test may, under certain conditions, be carried out without class attendance prior to the annual survey.


By preparing test procedures and conducting tests prior to the annual surveys, vessels can limit the impact of annual surveys on the daily operations.

References and more information

DNV GL rules for classification: Ships (RU-SHIP): Pt. 7 Fleet in service, Ch.1 Survey requirements for fleet in service ‒ Sec. 2 [3.1.5]

Document code: DNVGL-RU-SHIP-Pt7Ch1


Annex I: Guidelines for standby functionality test procedure (see on page 3 in PDF version of this technical news)


07 July 2023

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