Landing light CB

Jim Weir wrote in message . ..
(Dan Thomas)
shared these priceless pearls of wisdom:


- The 4522 bulb is a 250 watt bulb at 13 volts.

Read the original post. The poster said it was a 4552, not a 4522. The 4552 is
a 250 watt bulb at 28 volts.



That translates into
-19.23 amps. As the charging system comes into play the voltage rises
-to 14 volts, and assuming that the resistance of the bulb doesn't
-change much, the current flow rises to 20.71 amps. The breaker will
-pop after a bit, especially if it's old. It's a Cessna engineering
-screwup.

Hardly. The aircraft would never have been certified with a breaker running
that close to limits.


- We have a 172 with the same system. We had to increase the breaker
-to 25 amps (and go to #10 wire to satisfy AC43.13 requirements for
-current flow) to eliminate nuisance tripping.

Well, ONE of you is wrong. Either the original poster made a typo or you made
an incorrect interpretation. Tell me, though, just for grins, what year and/or
model 172 had this "engineering screwup" so that I can go back through the TCDS
and parts list to see where the screwup really is.

1972 172L. All breakers and bulbs were as per parts manual.

Dan

Well, ONE of you is wrong. Either the original poster made a typo or you
made
an incorrect interpretation. Tell me, though, just for grins, what year
and/or
model 172 had this "engineering screwup" so that I can go back through the
TCDS

Ok here are the facts.
The plane is a 1973 Cessna 172 M.
The landing light is a 4522. 250 watt at 14 volts. By ohms law is draws 17.86
amps.
The Circuit Breaker Part number is S-1360-20---20 amp
This is from the equipment table on page 20-35
Either the Cessna book is wrong or the light should be of lower wattage or the
circuit breaker should be of a higher amperage.
Hank