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Date: 02/01/00 at 10:37 AM
Posted by: John Dunn - Consultant
E-mail: ambertec@ieee.org

In Reply to: need to understand lamp enigma posted by delaporte on 02/01/00 at 6:34 AM:

: Can you explain why at the end of life of an incandescent lamp, when the filament break, sometime, the fuse break too.
: Some people in our company made measures of the thermal contraint with different sort of lamp and found 55A*A*t in the worst case.
: I don't understand the explanation of the phenoména.

Hi, Delaporte:

I don't have a definitive answer, but permit me to speculate.

Suppose that the two wire supports for the filament were a distance "L" apart. Suppose also that the lamp's filament which straddles that distance is actually longer than "L", but looped in some fashion during normal use. If when the filament breaks, a piece of it falls across the two support wires, it could momentarily re-establish an electrical connection having only a fraction of the resistance value of the original filament. There would be a brief but large current pulse which might be enough to blow out the fuse.

Good luck.

John Dunn -- President
Ambertec, Inc.
ambertec@ieee.org

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