Today's Message Index:
----------------------
1. 06:19 AM - Re: Securing Split PVC Conduit (user9253)
2. 06:44 AM - Re: Re: Securing Split PVC Conduit (Art Zemon)
3. 09:13 AM - Re: Securing Split PVC Conduit (Neal George)
4. 11:31 AM - Re: Securing Split PVC Conduit (Hal Benjamin)
5. 03:07 PM - Re: Securing Split PVC Conduit (Holger Selover-Stephan)
6. 06:25 PM - Re: A couple of questions about Fuses (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: Securing Split PVC Conduit |
Is conduit necessary inside of a channel?
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=464426#464426
Message 2
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| Subject: | Re: Securing Split PVC Conduit |
When there are sharp things sticking into the channel, yes
On Tue, Dec 27, 2016 at 8:18 AM, user9253 <fransew@gmail.com> wrote:
>
> Is conduit necessary inside of a channel?
--
https://CheerfulCurmudgeon.com/
*"If I am not for myself, who is for me? And if I am only for myself, what
am I? And if not now, when?" Hillel*
Message 3
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| Subject: | Re: Securing Split PVC Conduit |
A dab of RTV?
Neal George
Sent from my iPhone
> On Dec 26, 2016, at 10:05 PM, Art Zemon <art@zemon.name> wrote:
>
> Folks,
>
> I am using some split PVC conduit in my plane and two of the runs are pret
ty close to vertical, about 4 feet long. Sitting in my garage, with the wire
s not yet secured at the bottom, the conduit keeps trying to slide downward i
n the 2 inch square channels through which it runs. I think that I ought to s
ecure it somehow and wonder if you have any ideas that will keep it in place
.
>
> Maybe I can wrap a thin cable tie around it and get it to slip into a groo
ve?
>
> Or maybe wrap it with silicone self-sealing tape and the put an AN742 clam
p around it?
>
> Thanks,
> -- Art Z.
>
> --
> https://CheerfulCurmudgeon.com/
>
> "If I am not for myself, who is for me? And if I am only for myself, what a
m I? And if not now, when?" Hillel
Message 4
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| Subject: | Re: Securing Split PVC Conduit |
Hi Art,
You could probably use safety wire wrapped around the split loom and hang it
using tape to hold the safety wire.
Hal Benjamin RV4
Sent from my iPad
> On Dec 26, 2016, at 10:05 PM, Art Zemon <art@zemon.name> wrote:
>
> Folks,
>
> I am using some split PVC conduit in my plane and two of the runs are pret
ty close to vertical, about 4 feet long. Sitting in my garage, with the wire
s not yet secured at the bottom, the conduit keeps trying to slide downward i
n the 2 inch square channels through which it runs. I think that I ought to s
ecure it somehow and wonder if you have any ideas that will keep it in place
.
>
> Maybe I can wrap a thin cable tie around it and get it to slip into a groo
ve?
>
> Or maybe wrap it with silicone self-sealing tape and the put an AN742 clam
p around it?
>
> Thanks,
> -- Art Z.
>
> --
> https://CheerfulCurmudgeon.com/
>
> "If I am not for myself, who is for me? And if I am only for myself, what a
m I? And if not now, when?" Hillel
Message 5
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| Subject: | Re: Securing Split PVC Conduit |
I=99ve used lacing tape for that purpose in the past. So friendly
to do-overs.
Holger
> On Dec 26, 2016, at 7:05 PM, Art Zemon <art@zemon.name> wrote:
>
> Folks,
>
> I am using some split PVC conduit
<http://www.hall-fast.com/consumables/electrical/cable-accessories/conduit
-and-warning-tapes/pvc-split-conduit/> in my plane and two of the runs
are pretty close to vertical, about 4 feet long. Sitting in my garage,
with the wires not yet secured at the bottom, the conduit keeps trying
to slide downward in the 2 inch square channels through which it runs. I
think that I ought to secure it somehow and wonder if you have any ideas
that will keep it in place.
Message 6
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| Subject: | Re: A couple of questions about Fuses |
In my fused power busses I decided to use LED blade fuses, those
whose LED gets illuminated when the fuse trips.
Are you anticipating replacement of fuses in flight?
It happens that I have a couple of circuits which require a 1A fuse,
but there are no 1A LED blade fuses. Therefore, in these circuits,
either I use a normal (non-illuminated) 1A fuse, or I go for a 2A
illuminated fuse.
I used to sell 1 and 2A ATC fuses but
never with failure annunciation. If your
appliance is 'dead in the water', little
lights on the fuses are of marginal convenience.
What happens if I decide for the latter? Do I get less protection? Is
that particular device more prone to be fried?
"Less" and "more" are hard to quantify.
What we do know is that legacy wire
protection philosophy is based not upon
wire size but the robustness of the
insulation. You can purchase 22AWG wires
with recommended maximum operating
temperatures all over the map . . . generally
no lower than 80C but some as high as
180-200C. In EVERY case, it is not the
wire at-risk for failure due to effects
of current flow . . . it's the INSULATION
that drives the numbers on max recommended
temperature rise.
Wrestling with the consequences for choosing
1A vs 5A protection on a 22AWG wire is
not particularly difficult.
See http://tinyurl.com/zrmkoz6
That image demonstrates that loading
a 22AWG wire at 20 amps does not produce
a free-air temperature rise that places
the Tefzel insulation at risk for failure.
Now, for the second question, in a broader perspective: I have heard
dozens of times that a fuse (or other protection device) is there to
protect the wire and not the device at its end.
Absolutely . . .
However, the size (in A) of the fuse is determined by the device in
use (you read in the installation manuals that "to protect this
device, you should use a 3A fuse or circuit breaker").
People who write installation manuals are
almost never system integrators. Frequently
they are not talented writers either. The
installation manuals should speak to continuous
and intermittent current drain values. Intermittent
values should also be quantified with a typical
duration.
It's up to the system integrator to supply
a source of energy that is (1) not at risk
for tripping its feeder protection. (2)
sizing the wire such that its temperature rise
does not exceed ratings for the proposed
insulation. Allowances must be made for
areas where the wire may traverse an
elevated environmental temperature. Further
consideration is made for loss of cooling
the wire is bundled. (3) The final consideration
evaluates potential for loss of appliance
performance due to voltage drop when the run
of wire is particularly long. Lear got
bit in the cushy behind when they discovered
an unacceptable loss of performance for a pitch
trim system because motor current ran the
length of the aircraft four times!
While the wires were not over-heating, the
voltage drop under certain conditions produced
unsatisfactory trim performance. I got to design
a solid state fleet retrofit trim controller.
My boss was really happy with that one . . .
got a big raise. He paid for my flying lessons
accompanied by a generous flying budget from the
rental fleet at United Beechcraft.
I know that this depends on the power (W) that is used by the device
when working, and that both the wire and the fuse must be sized
accordingly. I also know that if we use a thinner wire, it will get
very hot and eventually melt.
But what about using an higher A or a lesser A fuse? What are the
physics involved?
The copper wire is never at-risk except conditions
where ship's batteries can drive a hard-fault
of hundreds if not thousands of amps. So in
the photo example cited above, I COULD
consider running a 20A appliance through
a 22AWG feeder protected with a 30A fuse . . .
as long as the feeder length wasn't so long
that voltage drop becomes an issue.
When selecting wires and protection, you're
never wrong with the "legacy pairs" of
22AWG/5A, 20AWG/7A, 18AWG/10A, etc. etc.
These are very conservative pairings.
An installation manual should read something
like, "Supply DC power at 11-15 volts with
a continuous demand of X.X amps and a 10%
duty cycle of Y.Y amps."
After that, it's up to the system integrator
to meet that requirement. I would never have
attempted to qualify a product that begged
for EXTERNAL overcurrent protection beyond
that normally supplied with the recommended
wire size. If you've got a 22AWG feeder to
a device where 3A protection is suggested,
5A protection is not out of line.
Bob . . .
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