Why the blackout that led to the fatal collision occurred on M/V Dali? Impressive animation by the NTSB and reminder on the importance of workmanship and quality control.
This animation depicts the method of connecting electrical wires using terminal blocks on the Dali. The first image shows photographs of electrical control panels on the Dali. The next image shows a photograph of wires connected through terminal blocks; each wire has a numerical label that matches the numerical label on the terminal block where it is inserted. The photograph shows terminal blocks 362 through 389.
A close-up view of the end of a wire shows that it is terminated with a metal sleeve called a ferrule; the wire also has a labeling band wrapped around the insulation with the number 382 on it. Text on the screen identifies the ferrule and the labeling band.
An image shows four terminal blocks arranged side by side with wires inserted into the connecting ports; the terminal blocks and wires have labels 381 through 384. The terminal blocks are rotated to zoom in on one connecting port, focusing on the spring clip and the internal conductor bar; the image is identified in text as a cut-away view of the mechanism. A tool is inserted down into a side port adjacent to the connecting port, which pushes the spring clip open and allows a ferrule to be inserted down into the connecting port. The tool is removed, and the spring clip closes, holding the ferrule firmly against the conductor bar .
An image compares two wire ends. On the first wire end, the labeling band with number 382 is placed on the insulation away from the ferrule. On the second wire end, the labeling band with number 381 is placed on the ferrule, increasing the diameter. Text on the screen indicates the labeling band position s.
The cut-away view of the mechanism is shown again. The tool is inserted and the spring clamp opened. A wire with a labeling band with number 381 on the ferrule is inserted but the larger diameter caused by the labeling band prevents the ferrule from being inserted fully. When the tool is removed and the spring clip closes, only the tip of the ferrule is held. The tip of the ferrule is shown slipping up out of the spring clip (which closes) and then down to rest atop the spring clip face. The ferrule then moves up a small amount to create a gap that prevents conduction of the electrical signa l.
Narra tion
1. The Dali electrical system distributes power and control signals throughout the ve ssel.
2. The control circuits contain hundreds of terminal blocks that organize thousands of wires.
3. The wires on the Dali were terminated with metal sleeves called ferrules that allowed for easier assembly into the terminal blocks.
4. Each wire was identified with a labeli ng band.
5. This image shows several terminal blocks on the Dali with wires c onnected.
6. To assemble a wire into a terminal block, a tool inserted into a side port opens a spring clamp, which allows the wire’s ferrule to slide into place.
7. Removing the tool closes the spring clamp, securing the ferrule firmly against the terminal block’s internal con ductor bar.
8. Labeling bands identify wires and are typically positioned on the wire insulation.
9. However, many labeling bands on the Dali wires were placed partially on the ferrules, which increased the ferrules’ overall ci rcumference.
10. As a result, during vessel construction, some of the ferrules could not be fully inserted in the terminal blocks, including the ferrule on wire 1 from Termin al Block 381.
11. On that wire, the labeling band prevented full insertion of the ferrule, so the spring clamp gripped only the ferrule’s tip, resulting in an inadequ ate connection.
12. Due to this unstable connection, over time the ferrule on wire 1 slipped out of the spring clamp to rest atop the spring clamp face, resulting in a precarious electr ical connection.
13. When a gap occurred between the ferrule and the spring clamp face, the electrical circuit was interrupted, leading to a blac kout on the Dali.