nuckolls.bob(at)cox.net
Guest
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 Posted: Sat Apr 12, 2008 1:20 pm Post subject: Alternate Feed Switch, is it a Master Switch?? |
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At 11:52 AM 4/12/2008 -0700, you wrote:
| Quote: |
Thanks Bob for an exceptional and thorough response. You very clearly took
the most of the "fog" out of my feeble interpretation of Section-23-1361.
I'll be able to better make my 337(Field Approval) case to FAA now, as
well as educate my friend.
> The point of disconnection must be adjacent to the sources controlled by
> the switch arrangement.
>
> Yup, unless the feeder is limited to 5A or less as described below:
Does the above mean that the 5A rule applies only if there is no
disconnection adjacent to the source?
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Yes. Things like hour meters, clocks, dome lights, etc have
been attached directly to the battery and protected with 5A
breakers or fuses for decades. This allows a battery fed,
always hot wire to snake its way through the airplane to
do the intended task irrespective of whether or not the
battery master switch was ON.
| Quote: | Also, do you consider the 8" unprotected run from battery to Alternate
Feed switch to be excessive?
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Not sure about this question. The battery bus feeds should
always be protected by fuses or breakers, no matter how long.
The 8" rule is to avoid fusing things like jumpers that run
between the (+) side of a capacitor. bus isolation diode
(or similar device) and the power source. This is a special
case that doesn't apply to this conversation.
Whether your e-bus is simply switched or run through a
mini-battery contactor, it still gets protection right
at the battery.
| Quote: | If so, I can fuse it, or add the mini-contactor as you have suggested.
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I would recommend you go the mini-contactor route and
wire with 14AWG wire no matter what size fuse/breaker you
select. Even if you can get by with a 5A protected feeder
today, you may wish to upgrade it later. This is easily
accomplished if the local disconnect (relay) and wire
(14AWG) are already in place. The breaker or fuse can be
elevated to as high as 15A at a later time without taking
a hatchet to the wire bundles.
| Quote: | Also, I have heard that new Cessnas have Essential/Endurance buses
installed. Have you or anyone else heard of this and, if so, how did they
handle the Master Switch arrangement?
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I can find out. It would be pretty cool if they do this
now. About two years after I handed out several copies of the
'Connection to folks at the single-engine electrical engineering
group, a firewall mounted, single point ground system was
installed on production aircraft. I'll ask around.
| Quote: | A local Cessna dealer hinted that I could get their schematic by buying
the CD for several hundred dollars or by buying a new aircraft. [Shocked]
This forum seems much more user friendly. 
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Yeah . . . I can get one for the asking. I'll see
what I can do.
Bob . . .
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