I wonder what kind of diagnostics and logging they have for their power distribution?
If it was hooked to a circuit breaker, it wasn't a sub milliamp connection. A thermal camera might have been able to see the heat from arcing at the connection point. It could have caused a hot spot visible on thermal imaging.
According to "3 - ENGINEERING - DALI - ENGINEERING FACTUAL REPORT"[5], page 20, the circuit was DC, 110 volts, going to a circuit breaker's "under voltage release" terminal. It was 17 AWG, according to page 23.
It apparently goes to a solenoid, and if [6] is in any way typical, it's only 2-6 watts of power in normal operation. This yields a current of 20-50 milliAmps.
Here's a nice animation of the connection failure on that wire.[4]
[1] https://www.ntsb.gov/investigations/Documents/Board%20Summar...
[2] https://www.digikey.com/en/products/detail/wago-corporation/...
[3] https://wago.priintcloud.com/datasheets/280-681/en_GG/d41d8c...
[4] https://www.youtube.com/watch?v=bu7PJoxaMZg
[5] https://data.ntsb.gov/Docket/Document/docBLOB?ID=19228257&Fi...
The wire in question was carrying unknown current (likely 20-50 mA), but 110 volts DC signaling.
Comparing the photos on page 22 (Dali) and 25 (Cezanne), you can clearly see the blue ferrules in the correctly wired panel on the Cezanne.
[1] https://data.ntsb.gov/Docket/Document/docBLOB?ID=19228257&Fi...
ghostly_s•2mo ago
rolph•2mo ago
"That sticker, identifying the line, kept the wire from getting a good connection in a circuit breaker – which in turn ultimately caused the first blackout. "