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I can understand the confusion on this (logic wise) but the answer for
me are the real world causes of over-current conditions.
A fault in equipment can cause an over-current condition and
still leave the device completely or partially
operational. A solder splash or metal chip bouncing around can do it
too. Any number of unanticipated things in a wiring harness can
cause an intermittent short (wire chaffing etc.). We like to
think our wiring skills would never allow this to happen but these things
*do* occur, especially when builders are new to electrical wiring.
On the ground it probably makes more sense to fuse or CB the circuit closer
to the actual load. It *might* prevent further damage to the
equipment. The game is completely different in the air. I want the
last second of operation out of every piece of gear on the plane when I'm in the
air. I'll worry about the cost of repairs later when I'm safely on the
ground.
Others have already stated the right reason for protecting the
wire: Prevention of in-flight fire or smoke in the cockpit. That is
the ONLY reason I want any system on the plane to shut down.
Tracy
----- Original Message -----
Sent: Saturday, October 21, 2006 8:43
AM
Subject: [FlyRotary] Re: Fuse Ratings for
Wiring??
Yes, Bill, that is what I understand as well. BUT, if you
are fused for the
equipment load, the wiring is automatically protected
(in a proper design).
In fact, by using a smaller rated fuse (designed
just to protect the
equipment rather than the wiring) you are even better
ensuring that the
wiring won't carry a dangerous load and catch
fire. So again, I can see no
rational reason for fusing to protect
the wire rather than a lower rated
fuse/CB to protect the equipment
(regardless of whether it actually protects
the equipment). But,
then I've never been accused of being the brightest
turnip on the tomato
truck.
Ed
----- Original Message -----
From: "Bill Schertz"
<wschertz@comcast.net>
To: "Rotary
motors in aircraft" <flyrotary@lancaironline.net>
Sent:
Friday, October 20, 2006 11:24 PM
Subject: [FlyRotary] Re: Fuse Ratings for
Wiring??
> Ed,
> I think the objective is to keep from
having a wire-induced fire when you
> get a short to ground. If the
insulation rubs and a short develops, you
> want a fuse/breaker sized
to pop before the wire melts and causes a fire.
>
> If the
equipment has an internal problem, the fuse/breaker isn't going to
>
help save it.
> Bill Schertz
> KIS Cruiser # 4045
> -----
Original Message -----
> From: "Ed Anderson" <eanderson@carolina.rr.com>
>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
>
Sent: Friday, October 20, 2006 5:12 PM
> Subject: [FlyRotary] Fuse
Ratings for Wiring??
>
>
>> One thing I have never
really understood regarding fuses (or CB for
>> that
matter) is - why you would use a fuse/CB with the rating set to
>> protect the wire!!! If you have a system operating
off a power wire, it
>> is highly likely that the wire will flow
much more current than the
>> system requires by quite a bit.
So if you select a fuse or CB rating
>> that protects the equipment
then automatically it will protect the wire.
>>
>>
However, if you select the rating to protect the wire, the system could
>> easily fry and the fuse or CB might never trigger. Just one
of those
>> things (wire size) that everybody uses as a guide for
selecting the
>> ratings (Fuse/CB) and yet, it has never made sense
to me (and still does
>> not) {:>)
>>
>> I
guess IF you put more system load that used more current than a wire
>> was rated for then a fuse sized for the system would not protect
the wire
>> which could over heat. But, that is simply a bad
wiring decision in
>> selecting too small a wire in the first place.
I guess the rational is
>> better the system fry than the wire - but
not certain I buy it.
>>
>> I don't really lose sleep over
this one - but, I do wonder from time to
>> time about things we
come to accept {:>)
>>
>>
>>
Ed
>>
>>
>>
>>
>> ----- Original
Message -----
>> From: "Ed Anderson" <eanderson@carolina.rr.com>
>>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
>>
Sent: Friday, October 20, 2006 5:47 PM
>> Subject: [FlyRotary] Re:
Injector Switches !!! was Re: Powering fuel
>>
injectors
>>
>>
>>> Welcome,
Greg.
>>>
>>> Yes, there are arguments pro and con
about fuses and CB - its about the
>>> only thing I disagreed
with Bob Nuckolls about {:>). Probably
>>> influenced by
my years flying military aircraft - where CB are
>>> everywhere
and fuses no where {:>)
>>>
>>> In any case, glad
you are now aware of the "disable" switch function
>>> regarding
doubling the fuel flow through on pair of injectors when the
>>>
other is turned off. You can fly easily on one pair - provided it is
>>> doing double duty with the fuel
flow.
>>>
>>>
Ed
>>>
>>>
>>>> Thanks for that
Ed, I am using the EC2 but I hadn't gone through the
>>>> install of it thoroughly yet and wasn't aware of that
mode. I'll make
>>>> sure that it's done
now.
>>>>
>>>> I follow what you're saying about
breakers instead of fuses and I have
>>>> to agree, but
following the Bob Nuckolls school of wiring means that
>>>>
the fuses/breakers should be no more than 6" to a foot from the power
>>>> source (battery) and the batteries are behind the rear
baggage area and
>>>> no where near the panel. The
argument for the fuses to be near the
>>>> source of electric
power is also valid considering the fuses are there
>>>> to
protect the wiring.
>>>>
>>>>
Greg
>>>>
>>>>
>>>>> Hi
Greg,
>>>>>
>>>>> Looks like a good
electrical system over all. However, I would
>>>>> not feel comfortable with fuses in my critical system
power line.
>>>>> But, I see that you are routing two power
sources to each switch of
>>>>> your critical system which
means if one fuse blows due to a transit
>>>>> spike, the
other one, hopefully, will not. Again, this is my own
>>>>> personal bias against fuses in critical systems -
there are arguments
>>>>> to the contrary for
sure.
>>>>>
>>>>> One thing I did notice,
is looking at your injector power switches, I
>>>>> am not
certain if these are meant to be the same as Tracy Crook's
>>>>> Injector disable switches. If they are (and
they may not be), I do
>>>>> not see the connection that
automatically grounds the "cold Start"
>>>>> mode in the
EC2 when either injector pair are disabled (turned
off).
>>>>>
>>>>> This may be a
detail just not shown on the drawing - but it is
>>>>>
crucially important. If the injector power switch does not have the
>>>>> "cold start" grounding provision, then if you ever
switch off one of
>>>>> the injector pairs, your fuel flow
will drop approx by 1/2 half. The
>>>>> reason is
that (with Tracy's recommended switch set up) when you turn
>>>>> off one pair of injectors , that automatically
grounds the "cold
>>>>> start" pin which causes the EC2 to
double the duration of the PW
>>>>> (Pulse Width) signal to
the remaining injector pair. This in turn
>>>>>
doubles the amount of fuel from the active pair of injectors. If the
>>>>> "cold start" is not activated (by automatic grounding
of the cold
>>>>> start pin through a DPDT switch) when an
injector pair is switched
>>>>> off, then the PW
signal does NOT double and the fuel flow through the
>>>>>
one injector pair will only be 1/2 of what the engine
needs.
>>>>>
>>>>>
>>>>>
Ed
>>>>>
>>>>> Ed
Anderson
>>>>> Rv-6A N494BW Rotary
Powered
>>>>> Matthews, NC
>>>>> eanderson@carolina.rr.com
>>>>>
http://members.cox.net/rogersda/rotary/configs.htm#N494BW
>>>>>
http://www.dmack.net/mazda/index.html
>>>>>
>>>>>
----- Original Message -----
>>>>> From: "Greg@itmack" <greg@itmack.com>
>>>>>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
>>>>>
Sent: Friday, October 20, 2006 3:33 AM
>>>>> Subject:
[FlyRotary] Re: Powering fuel
injectors
>>>>>
>>>>>
>>>>>>
I'm trying to keep the number of switched down as well, I attached a
>>>>>> pdf
>>>>>> with my schematic
which is a work in progress for your
review.
>>>>>>
>>>>>> I have noted
that a lot of builders reduce a lot of this complexity
>>>>>> by just
>>>>>> hanging
everything off 1 or 2 fuses which is fine until a fuse blows
>>>>>> and
>>>>>> then everything
stops.
>>>>>>
>>>>>> Greg RV8 down
under
>>>>>>
>>>>>>
>>>>>>
>>>>>>>I
am using Z-19 from the Aeroelectric Connection as a guide for
>>>>>>>wiring
>>>>>>> my
plane. I would like to power the injectors from the battery
>>>>>>> buss.
>>>>>>> Looking
at Z-19, do I need to install a complete switch and diode
>>>>>>> system
>>>>>>> for
the injectors like is done for the fuel pump and ECU, or can I
>>>>>>> tie
>>>>>>> on to the
fuel pump OR the ECU system after either the switch (add
a
>>>>>>> separate diode) or after one of the
diodes?
>>>>>>> There will be the two DPDT switches to
disable the primary and
>>>>>>>
secondary
>>>>>>> injectors after this
connection.
>>>>>>> My panel is becoming somewhat
switch festooned and I would like to
>>>>>>>
keep
>>>>>>> more switches to a
minimum.
>>>>>>> How have you guys accomplished
this?
>>>>>>>
>>>>>>>
Thanks.
>>>>>>> Bill
B
>>>>>>>
>>>>>>>
>>>>>>>
--
>>>>>>> Homepage: http://www.flyrotary.com/
>>>>>>>
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>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>>
--------------------------------------------------------------------------------
>>>>>
>>>>>
>>>>>>
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>>>>>> Homepage: http://www.flyrotary.com/
>>>>>>
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>>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
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>>>>> Homepage: http://www.flyrotary.com/
>>>>>
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>>>>>
>>>>>
>>>>
>>>>
>>>>
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>>>> Homepage: http://www.flyrotary.com/
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>>>>
>>>
>>>
>>>
>>>
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>>> Homepage: http://www.flyrotary.com/
>>>
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>>>
>>
>>
>>
>>
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>
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