[Public-List] testing my mast head light

[gregr at nethere.com]

Hi Jeff,

Something I've seen more than once:
A light stops working.
You pull the bulb and it tests fine on the bench.
You check the socket with the switch on and find you have 12V.
So what gives?
Corrosion may have got ya. What happens is your meter, by design, doesn't
load the circuit. Even corroded wire/contacts can pass the really tiny
current the meter uses to make a voltage reading (12V/10M ohm = 1.2uA).
However that same corroded wire/contact can't pass the current of a 10W bulb
(10W/12V = 0.83A  0.83A/1.2uA ~ 700,000 times more current).

Regards,

Greg
#43 Ayla

 1338824886.0