Beecrofter wrote:


Tungsten has a positive temperature coefficient of resistance, so a cold
lamp filament has a much lower resistance than it does at operating
temperature. The reason one sometimes sees a lower "Tungsten" rating
specified for switches and relays is because when an incandescent lamp
is turned on it results in a high initial surge current until the
filament heats up.

John

Actually that is bass ackwards
Tungsten filaments have a negative temperature coefficient.
Temperature rises conductivity decreases.


You're both right but you're talking about different things. The
resistivity temperature coefficient is positive, which makes the
conductivity temperature coefficient negative. At any rate, the inrush
current through a tungsten filament is much higher than the operating
current.