Page 14 - April 25

FROM THE TRAINING CENTER
A failed 325a current limiter
Current Limiters … Again
by Zach Cleaver
about them and we test
Current limiters: We talk
them. But what do they
do for us, and how can
we protect them?
Let’s start with defining a
current limiter. It’s a device that
restricts or limits electrical flow
to a predetermined maximum
amount that prevents damage to
components.
The most talked about current
limiters in King Airs are the 325
ampere limiters found in the dual-
fed electrical system design (see
Figure 1) so that’s what we are going
to focus on in this article.
What do the 325a current limiters
protect? They control the amperage
flowing between the isolation bus
to the left main bus and the right
main bus. The first time we check
the current limiters is during our
cockpit preflight checks. The battery
is on and we press the button on our
load meters to show the voltage to
Figure 1
the left and right main buses. If the
voltage reads battery volts, we know
that our current limiters are intact.
If one of the volt meters shows zero
volts, the current limiter on that
side has failed and will need to be
replaced.
How can we protect
325a current limiters?
The time that the current limiters
are most vulnerable to damage is
during engine start. Let’s look at
how that happens.
The generator-assisted start
that I will describe offers the best
protection for your current limiters
and can be used in any King Air.
Newer King Airs (BB-1444 and
newer) and triple-fed bus electrical
system King Airs can perform a
true cross-generator start without
damaging the current limiters.
Check your POH to make sure
your plane is capable of the cross-
generator start. If you have doubts,
using the generator-assisted start
technique will help keep your
current limiters safe.
12 •
­ KING AIR MAGAZINE APRIL 2025