[time-nuts] Filament type lamps as a test fuse...

Burt I. Weiner biwa at att.net
Thu Sep 10 13:46:20 UTC 2009

I've done that many times when trouble shooting power supply 
issues.  In fact, about 25 years ago I built a "test fixture" using 
two electrical type boxes.  One box has a light bulb socket and the 
other has a duplex outlet socket.  Pick the appropriate light bulb 
for the occasion.  On the light bulb box there's a strain relief like 
the type used for Romex and a 6' A.C. cord and plug.  I'm surprised 
how often I've used this little test fixture.  It's more than paid 
for itself in fuses I haven't had to blow!

Burt, K6OQK

At 05:00 AM 9/10/2009, Dave B at time-nuts-request at febo.com wrote:
>Filament lamps have the nice PTC feature, that when cold they have a
>lower resistance than when hot, so for no fault conditions, things can
>actually work quite well.  When the fault happens, the lamp lights,
>"Indicating" the problem, but not letting too much current flow to cause
>more damage.
>It's a simple trick, but one I've used on many an occasion, from 12V
>vehicle electrics, right up to 240V AC House electrics with a 60W lamp!
>(Unscrambling a nightmare caused by a so called "Professional"
>electrician, who walked away from the job, leaving multiple shorts in
>the lighting circuit.)
>I make no claim for originality, as I learnt the trick when working for
>BT (the Telephone co in the UK) years ago, but it's stood me in good
>stead on many occasions with various "Barsteward" electrical woes...
>I even used to have an old television of my own (I was given it!) where
>I ended up with a 24V bulb in series with the DC feed to the line output
>driver transistor, because that used to "Pop" on odd occasions.  I never
>found out why (neither did the TV repair guy, which is why I ended up
>with it I guess) but for some years (until I donated the TV to a local
>hospice) if you turned it on and got no picture, just cycle the power
>and it'd come up OK the next time, not needing any surgery!   That used
>to happen on average about once every week or two from memory.
>Dave B.

Burt I. Weiner Associates
Broadcast Technical Services
Glendale, California  U.S.A.
biwa at att.net

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