Aluminum Wiring to Blame ? Japan article on Boeing has this comment
BuzzBJan. 22, 2013 - 08:07PM JST
I have my eye on the aluminum wire on this plane. It is a well known fact that aluminum wire is tricky to employ especially where there are extremes in temperature and vibration. There is a reason it was outlawed in building wiring systems. Also, do we fully understand how current flows in/on aluminum wire. I've been an electrician for over 40 years. We always learned that DC travels inside the copper wire and and AC travels on the outside surface. This is known as the "skin effect". Airplanes usually employ 400 Hz AC as well as DC. 28 volts DC used to be the standard but I'm betting all these old rules have been bent and twisted for "cutting edge" advantage. So are these aluminum wire bundles a mixed bag? With DC circuits and AC circuits alongside each other? I know how inductive coupling of AC circuits works on copper lines but am not knowledgeable about how that works on aluminum. These systems were no doubt tested to great length individually without fail. But how do they all get along in a big crowd?? If it turns out to be inductive coupling then this will be a costly fix for sure
The NTSB has stated that the incident in Boston was teh result of a failure in a single cell of the battery. It was operating normally at about 32 volts and suddenly dropped to 28 volts which is the voltage in each cell. What they dont know yet is why the cell shorted. I am not sure how they would be able to determine the exact cause of the short.