Today's Message Index:
----------------------
1. 06:36 AM - Re: Melted wire (flyv35b)
2. 07:52 AM - Re: Melted wire (Bob Steward)
3. 08:08 AM - Re: Re: Melted wire (Rick Lindstrom)
4. 08:11 AM - Re: Re: Melted wire (Hosler, John)
5. 08:16 AM - Re: Melted wire (n76lima@mindspring.com)
6. 08:19 AM - Re: Re: Melted wire (n76lima@mindspring.com)
7. 11:29 AM - Re: Melted wire (Gary Vogt)
8. 11:38 AM - Re: Re: Melted wire (Gary Vogt)
9. 11:39 AM - Re: Re: Melted wire (Gary Vogt)
10. 11:40 AM - Re: Re: Melted wire (Gary Vogt)
11. 11:49 AM - Re: Re: Melted wire (Mel Beckman)
12. 12:18 PM - Re: Re: Melted wire (FLYaDIVE)
13. 12:25 PM - Re: Re: Melted wire (Gary Vogt)
14. 12:25 PM - Re: Re: Melted wire (Curt Johnson)
15. 12:38 PM - Re: Re: Melted wire (FLYaDIVE)
16. 12:39 PM - Re: Re: Melted wire (Gary Vogt)
17. 12:56 PM - Re: Melted wire (n76lima@mindspring.com)
18. 01:33 PM - Re: Re: Melted wire (Mel Beckman)
19. 07:28 PM - Re: Melted wire (beltz6)
Message 1
| INDEX | Back to Main INDEX |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
On 9/23/2012 7:45 PM, n76lima@mindspring.com wrote:
>
> [Gary] IF there is a significant corrosion in the areas where the plastic shield
is, would there be enough resistance to make the wire heat more? I replaced
the entire wire with #18 wire.
>
> The problem is that the power is applied to the coil internally in the Master
Relay, and then this wire is a GROUND. A #2 gauge jumper cable would not carry
anymore current than the OEM wire, because the limiting resistance is at the
SOURCE (power goes through the positive cable to the Master Relay, and then
to the coil internally, and finally to a ground via the wire in question). One
can't really lower the resistance of the circuit by fiddling with the ground
wire. One can INCREASE the resistance, and thereby lessen the current, but no
way to externally to the Master Relay LOWER the resistance. So "corrosion"
on the wire would have no effect at increasing the current enough to heat it.
I suppose if enough strands were corroded through that the current of ~0.8 amps
would heat the wire locally, but the insulation would have to be off and the
corrosion damage happen BEFORE the heating, and since the supposition is that
the wire got hot FIRST, damaging the insulation, wh
i!
>
> ch could then lead to the corrosion and the narrowing of the wire, the chain
is completely backwards. And after the FIRST area was damaged (by whatever
means), then no further damage could occur down stream, since the current would
now be even MORE limited by the increased resistance at the first site damaged
on the wire.
>
> With several areas of damage, and wide spread lengths of heating, this is NOT
a localized problem of the wire losing a few strands to corrosion.
>
> Hence my suggestion that someone had replaced the Master Relay with a Starter
Relay, or that the relay had some sort of internal fault that was shorting power
to ground that did not go through the 15 ohm coil.
>
> --Bob Steward
>
>
Bob, what's the current draw of the coil in a starter contactor? Would
that even be enough to melt the insulation of an 18 ga wire? I assume
the wire was 18 ga. A single 18ga wire in free air wire should be able
to handle nearly 25 amp at conductor temp of around 150 C (100 C above
ambient). How would you get that kind of current flow without a direct
short to ground?
Cliff
Message 2
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
The coil in the Starter should have a resistance of ~2 ohms. So that means a current
of ~6 amps @ 12V.
Far below what the 18 ga. wire should safely carry.
The starter relay is usually wired differently than the Master. The Starter usually
has the coil isolated from the power terminals, and is POWERED by the start
button switch, rather than grounded.
It is also protected by the 10 amp fuse that powers the start/fuel pump/strobe
circuit.
So the wire powering the Starter relay is not subject to a ground fault, since
it would pop the 10 amp fuse before heating the wire.
The Master wiring might be subject a ground fault if some internal fault in the
relay allowed a lower resistance in the relay to overload the ground wire.
--Bob Steward
Message 3
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
I'm guessing here, without a wiring diagram in front of me, but wouldn't a
poor mechanical ground to the body of the starter solenoid result in all
current going through the 18 ga. wire instead?
If so, that would overheat the wire for sure.
Rick
On Mon, Sep 24, 2012 at 7:50 AM, Bob Steward <n76lima@mindspring.com> wrote:
> n76lima@mindspring.com>
>
> The coil in the Starter should have a resistance of ~2 ohms. So that
> means a current of ~6 amps @ 12V.
> Far below what the 18 ga. wire should safely carry.
> The starter relay is usually wired differently than the Master. The
> Starter usually has the coil isolated from the power terminals, and is
> POWERED by the start button switch, rather than grounded.
> It is also protected by the 10 amp fuse that powers the start/fuel
> pump/strobe circuit.
> So the wire powering the Starter relay is not subject to a ground fault,
> since it would pop the 10 amp fuse before heating the wire.
> The Master wiring might be subject a ground fault if some internal fault
> in the relay allowed a lower resistance in the relay to overload the ground
> wire.
> --Bob Steward
>
>
Message 4
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
The OEM ran the ground wire to the airframe with a sheet metal screw????
John
From: owner-teamgrumman-list-server@matronics.com
[mailto:owner-teamgrumman-list-server@matronics.com] On Behalf Of Rick
Lindstrom
Sent: Monday, September 24, 2012 11:08 AM
Subject: Re: TeamGrumman-List: Re: Melted wire
I'm guessing here, without a wiring diagram in front of me, but wouldn't
a poor mechanical ground to the body of the starter solenoid result in
all current going through the 18 ga. wire instead?
If so, that would overheat the wire for sure.
Rick
On Mon, Sep 24, 2012 at 7:50 AM, Bob Steward <n76lima@mindspring.com>
wrote:
<n76lima@mindspring.com>
The coil in the Starter should have a resistance of ~2 ohms. So that
means a current of ~6 amps @ 12V.
Far below what the 18 ga. wire should safely carry.
The starter relay is usually wired differently than the Master. The
Starter usually has the coil isolated from the power terminals, and is
POWERED by the start button switch, rather than grounded.
It is also protected by the 10 amp fuse that powers the start/fuel
pump/strobe circuit.
So the wire powering the Starter relay is not subject to a ground fault,
since it would pop the 10 amp fuse before heating the wire.
The Master wiring might be subject a ground fault if some internal fault
in the relay allowed a lower resistance in the relay to overload the
ground wire.
--Bob Steward
List"
target="_blank">http://www.matronics.com/Navigator?TeamGrumman-List
http://forums.matronics.com
le, List Admin.
="_blank">http://www.matronics.com/contribution
Message 5
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
The wire to the STARTER solenoid is POWERED, not grounded. The body of the starter
solenoid is isolated from the coil and the starter power circuits. One can
unbolt the starter solenoid from the firewall, and so long as the jumper wire
from the coil terminal to ground is maintained, it will function as it was
intended.
This thread started about a MASTER solenoid wire failing, and somehow morphed into
STARTER solenoid wiring discussion.
--Bob Steward
>From: Rick Lindstrom
>I'm guessing here, without a wiring diagram in front of me, but wouldn't a poor
mechanical ground to the body of the starter solenoid >result in all current
going through the 18 ga. wire instead?
>If so, that would overheat the wire for sure.
>Rick
Message 6
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
>From: "Hosler, John"
>The OEM ran the ground wire to the airframe with a sheet metal screw???? John
Yes, they did this at several locations. The instrument lights and compass light
are grounded to the honeycomb via a ring lug on the wiring and a sheet metal
screw.
The Magneto Ground at the ignition switch is also connected to the honeycomb via
the same method.
--Bob Steward
Birmingham, AL
Message 7
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
The wire in question, IS a direct short to ground. -It's a ground wire th
rough the Master switch. -I can't see where it would draw enough current
to get hot. -Yet, when I cut the wire and inserted an ammeter in series,
drawing just .65 to .7 amps, the wire got damn hot. -=0A=0ADon't you just
love electrical problems?-=0A=0A=0A________________________________=0A F
rom: flyv35b <flyv35b@minetfiber.com>=0ATo: teamgrumman-list@matronics.com
=0ASent: Monday, September 24, 2012 6:35 AM=0ASubject: Re: TeamGrumman-List
b@minetfiber.com>=0A=0AOn 9/23/2012 7:45 PM, n76lima@mindspring.com wrote:
[Gary] IF there is a significant corrosion in the areas where the plastic
shield is, would there be enough resistance to make the wire heat more?-
I replaced the entire wire with #18 wire.=0A>=0A> The problem is that the p
ower is applied to the coil internally in the Master Relay, and then this w
ire is a GROUND.- A #2 gauge jumper cable would not carry anymore current
than the OEM wire, because the limiting resistance is at the SOURCE (power
goes through the positive cable to the Master Relay, and then to the coil
internally, and finally to a ground via the wire in question).- One can't
really lower the resistance of the circuit by fiddling with the ground wir
e.- One can INCREASE the resistance, and thereby lessen the current, but
no way to externally to the Master Relay LOWER the resistance.- So "corro
sion" on the wire would have no effect at increasing the current enough to
heat it.- I suppose if enough strands were corroded through that the curr
ent of ~0.8 amps would heat the wire locally, but the insulation would have
to be off and the corrosion damage happen BEFORE the heating, and since th
e supposition is that the wire got hot FIRST,
damaging the insulation, wh=0A=0Ai!=0A>=0A>- ch could then lead to the
corrosion and the narrowing of the wire, the chain is completely backwards.
- And after the FIRST area was damaged (by whatever means), then no furth
er damage could occur down stream, since the current would now be even MORE
limited by the increased resistance at the first site damaged on the wire.
=0A>=0A> With several areas of damage, and wide spread lengths of heating,
this is NOT a localized problem of the wire losing a few strands to corrosi
on.=0A>=0A> Hence my suggestion that someone had replaced the Master Relay
with a Starter Relay, or that the relay had some sort of internal fault tha
t was shorting power to ground that did not go through the 15 ohm coil.=0A>
=0A> --Bob Steward=0A>=0A>=0A>=0A>=0A>=0ABob, what's the current draw of th
e coil in a starter contactor?- Would =0Athat even be enough to melt the
insulation of an 18 ga wire?- I assume =0Athe wire was 18 ga.- A single
18ga wire in free air wire should be able =0Ato handle nearly 25 amp at co
nductor temp of around 150 C (100 C above =0Aambient).- How would you get
that kind of current flow without a direct =0Ashort to ground?=0A=0ACliff
=========================0A
===================
Message 8
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
No, they didn't. -The ground from the Master goes to one of the screws th
at hold the instrument panel to the fuselage.=0A=0A=0A_____________________
___________=0A From: "Hosler, John" <JHOSLER@epri.com>=0ATo: teamgrumman-li
st@matronics.com =0ASent: Monday, September 24, 2012 8:11 AM=0ASubject: RE:
TeamGrumman-List: Re: Melted wire=0A =0A=0AThe OEM ran the ground wire to
the airframe with a sheet metal screw????=0A-=0AJohn=0A-=0AFrom:owner-t
eamgrumman-list-server@matronics.com [mailto:owner-teamgrumman-list-server@
matronics.com] On Behalf Of Rick Lindstrom=0ASent: Monday, September 24, 20
12 11:08 AM=0ATo: teamgrumman-list@matronics.com=0ASubject: Re: TeamGrumman
-List: Re: Melted wire=0A-=0AI'm guessing here, without a wiring diagram
in front of me, but wouldn't a poor mechanical ground to the body of the st
arter solenoid result in all current going through the 18 ga. wire instead?
=0A=0AIf so, that would overheat the wire for sure.=0A=0ARick=0AOn Mon, Sep
24, 2012 at 7:50 AM, Bob Steward <n76lima@mindspring.com> wrote:=0A--> Tea
mGrumman-List message posted by: Bob Steward <n76lima@mindspring.com>=0A=0A
The coil in the Starter should have a resistance of ~2 ohms. -So that mea
ns a current of ~6 amps @ 12V.=0AFar below what the 18 ga. wire should safe
ly carry.=0AThe starter relay is usually wired differently than the Master.
The Starter usually has the coil isolated from the power terminals, and is
POWERED by the start button switch, rather than grounded.=0AIt is also pro
tected by the 10 amp fuse that powers the start/fuel pump/strobe circuit.
=0ASo the wire powering the Starter relay is not subject to a ground fault,
since it would pop the 10 amp fuse before heating the wire.=0AThe Master w
iring might be subject a ground fault if some internal fault in the relay a
llowed a lower resistance in the relay to overload the ground wire.=0A--Bob
Steward=0A=0A=0A============0AList" target="_blank
">http://www.matronics.com/Navigator?TeamGrumman-List=0A======
======0Ahttp://forums.matronics.com=0A=========
===0Ale, List Admin.=0A="_blank">http://www.matronics.com/contributio
n=0A============0A=0A=0A=0A-=0A- http://www.matro
nics.com/Navigator?TeamGrumman-List=0A_============
========== http://forums.matronics.com -----
--- - List Contribution Web generous nbsp;---------
-------------- --> http://www.matronics.com/c
=====================
Message 9
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
The magneto ground should also be going to the instrument panel mount.=0A
=0A=0A________________________________=0A From: "n76lima@mindspring.com" <n
76lima@mindspring.com>=0ATo: teamgrumman-list@matronics.com =0ASent: Monday
, September 24, 2012 8:19 AM=0ASubject: RE: TeamGrumman-List: Re: Melted wi
=0A>From: "Hosler, John" =0A>The OEM ran the ground wire to the airframe wi
th a sheet metal screw???? John=0A=0AYes, they did this at several location
s.- The instrument lights and compass light are grounded to the honeycomb
via a ring lug on the wiring and a sheet metal screw.=0A=0AThe Magneto Gro
und at the ignition switch is also connected to the honeycomb via the same
=- - - - - - - - - - - - - - - -Matt Dralle
========
Message 10
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
on that subject, why is it (the magneto P-Lead shields) grounded at both en
ds?=0A=0A=0A________________________________=0A From: "n76lima@mindspring.c
om" <n76lima@mindspring.com>=0ATo: teamgrumman-list@matronics.com =0ASent:
Monday, September 24, 2012 8:19 AM=0ASubject: RE: TeamGrumman-List: Re: Mel
om=0A=0A>From: "Hosler, John" =0A>The OEM ran the ground wire to the airfra
me with a sheet metal screw???? John=0A=0AYes, they did this at several loc
ations.- The instrument lights and compass light are grounded to the hone
ycomb via a ring lug on the wiring and a sheet metal screw.=0A=0AThe Magnet
o Ground at the ignition switch is also connected to the honeycomb via the
===========
Message 11
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
You never ground radio-frequency interference (RFI) shields at both ends. Th
e objective of shielding is to absorb RFI, convert it to an electrical curre
nt, and drain the current to ground. If you ground the shielding at both end
it won't work, because no current can be induced in a conductor entirely at
ground potential. This is true for all RFI shielding, from ancient TV coax t
o the newest inter-building shielded Category-6 data cabling.
-Mel Beckman
On Sep 24, 2012, at 11:40 AM, Gary Vogt <teamgrumman@yahoo.com> wrote:
> on that subject, why is it (the magneto P-Lead shields) grounded at both e
nds?
>
> From: "n76lima@mindspring.com" <n76lima@mindspring.com>
> To: teamgrumman-list@matronics.com
> Sent: Monday, September 24, 2012 8:19 AM
> Subject: RE: TeamGrumman-List: Re: Melted wire
>
>
> >From: "Hosler, John"
> >The OEM ran the ground wire to the airframe with a sheet metal screw???? J
ohn
>
> Yes, they did this at several locations. The instrument lights and compas
s light are grounded to the honeycomb via a ring lug on the wiring and a she
et metal screw.
>
> The Magneto Ground at the ignition switch is also connected to the honeyco
mb via the samhare, and much much ==
>
>
>
>
>
>
>
==========================
=========
==========================
=========
==========================
=========
==========================
=========
>
Message 12
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
Mel:
In response to your email... It depends on what you want to accomplish.
Example:
In an RF (Radio Frequency) transmitter where there is shielding involved
you ground at both ends. An example of this would be a simple COAX cable
going to an antenna. COAX is an unbalanced medium and by grounding at both
ends (Radio & Antenna) you trap the signal and send it to ground via
the shortest path.
In an AF (Audio Frequency) intercom where you want to shield a transmitted
signal such as a RF transmission, you ground the shield (COAXIAL Shield
around the twisted pair of audio lines) at one end. The end you ground is
at the intercom, which is known as The Source <-- I know CRAZY since the
source of the interference is the RF. I don't know why they depict it that
way.
Think of it this way: In RF you don't want the signal to escape, you want
it to say contained within the shield. In AF you want the shield to act as
a fishing net and collect the signal and then send it to ground. And as
you said: " ... no current can be induced in a conductor entirely at ground
potential." <-- This is true in 99.9273% of cases. Where it gets foggy is
when you are talking WHAT FREQUENCY of RF and HOW LONG A GROUND WIRE. And
this stuff just starts to become a problem at our VHF frequencies and goes
really crazy at Microwave frequencies.
Barry
On Mon, Sep 24, 2012 at 2:49 PM, Mel Beckman <mel@becknet.com> wrote:
> You never ground radio-frequency interference (RFI) shields at both ends.
> The objective of shielding is to absorb RFI, convert it to an electrical
> current, and drain the current to ground. If you ground the shielding at
> both end it won't work, because no current can be induced in a conductor
> entirely at ground potential. This is true for all RFI shielding, from
> ancient TV coax to the newest inter-building shielded Category-6 data
> cabling.
>
> -Mel Beckman
>
> On Sep 24, 2012, at 11:40 AM, Gary Vogt <teamgrumman@yahoo.com> wrote:
>
> on that subject, why is it (the magneto P-Lead shields) grounded at both
> ends?
>
> ------------------------------
> *From:* "n76lima@mindspring.com" <n76lima@mindspring.com>
> *To:* teamgrumman-list@matronics.com
> *Sent:* Monday, September 24, 2012 8:19 AM
> *Subject:* RE: TeamGrumman-List: Re: Melted wire
>
>
> >From: "Hosler, John"
> >The OEM ran the ground wire to the airframe with a sheet metal screw????
> John
>
> Yes, they did this at several locations. The instrument lights and
> compass light are grounded to the honeycomb via a ring lug on the wiring
> and a sheet metal screw.
>
> The Magneto Ground at the ignition switch is also connected to the
> honeycomb via the samhare, and much much ==
>
>
> *
>
> ==================================
> t">http://www.matronics.com/Navigator?TeamGrumman-List
> ===================================cs.com
> ===================================matronics.com/contribution
> ==================================
> *
>
> *
>
> *
>
>
Message 13
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
Is the plane unairworthy if I remove the ground at one end? -It would not
longer meet type design.=0A=0A=0A________________________________=0A From:
Mel Beckman <mel@becknet.com>=0ATo: "teamgrumman-list@matronics.com" <team
grumman-list@matronics.com> =0ASent: Monday, September 24, 2012 11:49 AM=0A
Subject: Re: TeamGrumman-List: Re: Melted wire=0A =0A=0AYou never ground ra
dio-frequency interference (RFI) shields at both ends. The objective of shi
elding is to absorb RFI, convert it to an electrical current, and drain the
current to ground. If you ground the shielding at both end it won't work,
because no current can be induced in a conductor entirely at ground potenti
al. This is true for all RFI shielding, from ancient TV coax to the newest
inter-building shielded Category-6 data cabling.-=0A=0A-Mel Beckman-=0A
=0AOn Sep 24, 2012, at 11:40 AM, Gary Vogt <teamgrumman@yahoo.com> wrote:
=0A=0A=0Aon that subject, why is it (the magneto P-Lead shields) grounded a
t both ends?=0A>=0A>=0A>=0A>________________________________=0A> From: "n76
lima@mindspring.com" <n76lima@mindspring.com>=0A>To: teamgrumman-list@matro
nics.com =0A>Sent: Monday, September 24, 2012 8:19 AM=0A>Subject: RE: TeamG
rumman-List: Re: Melted wire=0A> =0A>--> TeamGrumman-List message posted by
: n76lima@mindspring.com=0A>=0A>>From: "Hosler, John" =0A>>The OEM ran the
ground wire to the airframe with a sheet metal screw???? John=0A>=0A>Yes, t
hey did this at several locations.- The instrument lights and compass lig
ht are grounded to the honeycomb via a ring lug on the wiring and a sheet m
etal screw.=0A>=0A>The Magneto Ground at the ignition switch is also connec
ted to the honeycomb via the samhare, and much much=0A====0A>=0A>=0A>
=0A>=0A>=0A>=0A>===================
=================0At">http://www.matronics.
com/Navigator?TeamGrumman-List=0A==============
===================== cs.com =
========= matronics.com/contribution=0A======
========================
Message 14
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
That's reversed. A conductor is not entirely at ground potential if
there is a current induced in it. Only at the ground connection is it a
zero potential. Everywhere else it differs by the product of the current
and the conductor impedance. That is a good reason to ground it at both
ends. I have seen shielded cables grounded every 6 inches to reduce the
amount of energy re-radiated from the shields.
You ground at one end only to eliminate ground loops.
Curt
On 9/24/2012 11:49 AM, Mel Beckman wrote:
> You never ground radio-frequency interference (RFI) shields at both
> ends. The objective of shielding is to absorb RFI, convert it to an
> electrical current, and drain the current to ground. If you ground the
> shielding at both end it won't work, because no current can be induced
> in a conductor entirely at ground potential. This is true for all RFI
> shielding, from ancient TV coax to the newest inter-building shielded
> Category-6 data cabling.
>
> -Mel Beckman
>
> On Sep 24, 2012, at 11:40 AM, Gary Vogt <teamgrumman@yahoo.com
> <mailto:teamgrumman@yahoo.com>> wrote:
>
>> on that subject, why is it (the magneto P-Lead shields) grounded at
>> both ends?
>>
>> ------------------------------------------------------------------------
>> *From:* "n76lima@mindspring.com <mailto:n76lima@mindspring.com>"
>> <n76lima@mindspring.com <mailto:n76lima@mindspring.com>>
>> *To:* teamgrumman-list@matronics.com
>> <mailto:teamgrumman-list@matronics.com>
>> *Sent:* Monday, September 24, 2012 8:19 AM
>> *Subject:* RE: TeamGrumman-List: Re: Melted wire
>>
>> <mailto:n76lima@mindspring.com>
>>
>> >From: "Hosler, John"
>> >The OEM ran the ground wire to the airframe with a sheet metal
>> screw???? John
>>
>> Yes, they did this at several locations. The instrument lights and
>> compass light are grounded to the honeycomb via a ring lug on the
>> wiring and a sheet metal screw.
>>
>> The Magneto Ground at the ignition switch is also connected to the
>> honeycomb via the samhare, and much much ==
>>
>>
>>
>>
>>
>> *
>>
>> ==================================
>> t">http://www.matronics.com/Navigator?TeamGrumman-List
>> ==================================
>> cs.com
>> ==================================
>> matronics.com/contribution
>> ==================================
>>
>> *
> *
>
>
> *
Message 15
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
Good question Gary...
But if it was supplied from the factory in working condition why would you
have to remove a ground. It would be more like putting the item back into
operational condition as supplied by the factory. Replace the wire back
to original condition.
So in this case you would not be changing the Type Design.
Now, when it comes to the addition of new equipment such as a new
GPS-Nav/Com or the classic case of Noise on the New Intercom [Problem
usually being - Shield Wire Grounded AT the Headphone & Mic Jacks]... Then
if you have a noise condition you do what is necessary to remove the noise.
If that entails removing a ground, so be it.
Barry
On Mon, Sep 24, 2012 at 3:24 PM, Gary Vogt <teamgrumman@yahoo.com> wrote:
> Is the plane unairworthy if I remove the ground at one end? It would not
> longer meet type design.
>
> ------------------------------
> *From:* Mel Beckman <mel@becknet.com>
> *To:* "teamgrumman-list@matronics.com" <teamgrumman-list@matronics.com>
> *Sent:* Monday, September 24, 2012 11:49 AM
>
> *Subject:* Re: TeamGrumman-List: Re: Melted wire
>
> You never ground radio-frequency interference (RFI) shields at both ends.
> The objective of shielding is to absorb RFI, convert it to an electrical
> current, and drain the current to ground. If you ground the shielding at
> both end it won't work, because no current can be induced in a conductor
> entirely at ground potential. This is true for all RFI shielding, from
> ancient TV coax to the newest inter-building shielded Category-6 data
> cabling.
>
> -Mel Beckman
>
> On Sep 24, 2012, at 11:40 AM, Gary Vogt <teamgrumman@yahoo.com> wrote:
>
> on that subject, why is it (the magneto P-Lead shields) grounded at both
> ends?
>
> ------------------------------
> *From:* "n76lima@mindspring.com" <n76lima@mindspring.com>
> *To:* teamgrumman-list@matronics.com
> *Sent:* Monday, September 24, 2012 8:19 AM
> *Subject:* RE: TeamGrumman-List: Re: Melted wire
>
>
> >From: "Hosler, John"
> >The OEM ran the ground wire to the airframe with a sheet metal screw????
> John
>
> Yes, they did this at several locations. The instrument lights and
> compass light are grounded to the honeycomb via a ring lug on the wiring
> and a sheet metal screw.
>
> The Magneto Ground at the ignition switch is also connected to the
> honeycomb via the samhare, and much much ==
>
>
> *
>
>
> ==================================
> t">http://www.matronics.com/Navigator?TeamGrumman-List
> =========
> cs.com
> ==========matronics.com/contribution
> ========== <http://matronics.com/contribution===================================>
> *
>
> *
> *
>
>
> *
>
> *
>
>
Message 16
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
Thanks Barry. -That was very well said and even I understood it. -I've
always wondered why both ends were grounded.=0A=0A=0A______________________
__________=0A From: FLYaDIVE <flyadive@gmail.com>=0ATo: teamgrumman-list@ma
tronics.com =0ASent: Monday, September 24, 2012 12:18 PM=0ASubject: Re: Tea
mGrumman-List: Re: Melted wire=0A =0A=0AMel:=0A=0AIn-response-to your e
mail... It depends on what you want to accomplish.=0A=0AExample:=0A=0AIn an
RF (Radio Frequency) transmitter where there is shielding involved you gro
und at both ends. -An example of this would be a simple COAX cable going
to an antenna. -COAX is an-unbalanced-medium and by grounding at both
ends (Radio & Antenna) you trap the signal and send it to ground via the
-shortest-path.=0A=0AIn an AF (Audio Frequency) intercom where you want
to shield a transmitted signal such as a RF transmission, you ground the s
hield (COAXIAL Shield around the twisted pair of audio lines) at one end. T
he end you ground is at the intercom, which is known as The Source <-- I kn
ow CRAZY since the source of the-interference-is the RF. -I don't kno
w why they depict it that way.=0A=0AThink of it this way: -In RF you don'
t want the signal to escape, you want it to say contained within the shield
. -In AF you want the shield to act as a fishing net and collect the sign
al and then send it to ground. -And as you said: "-...-no current can
be induced in a conductor entirely at ground potential." -<-- This is tr
ue in 99.9273% of cases. -Where it gets foggy is when you are talking WHA
T FREQUENCY of RF and HOW LONG A GROUND WIRE. -And this stuff just starts
to become a problem at our VHF frequencies and goes really crazy at Microw
ave frequencies.=0A=0ABarry=0A=0A=0A=0AOn Mon, Sep 24, 2012 at 2:49 PM, Mel
Beckman <mel@becknet.com> wrote:=0A=0AYou never ground radio-frequency int
erference (RFI) shields at both ends. The objective of shielding is to abso
rb RFI, convert it to an electrical current, and drain the current to groun
d. If you ground the shielding at both end it won't work, because no curren
t can be induced in a conductor entirely at ground potential. This is true
for all RFI shielding, from ancient TV coax to the newest inter-building sh
ielded Category-6 data cabling.-=0A>=0A>-Mel Beckman-=0A>=0A>On Sep 24,
2012, at 11:40 AM, Gary Vogt <teamgrumman@yahoo.com> wrote:=0A>=0A>=0A>on
that subject, why is it (the magneto P-Lead shields) grounded at both ends?
=0A>>=0A>>=0A>>=0A>>________________________________=0A>> From: "n76lima@mi
ndspring.com" <n76lima@mindspring.com>=0A>>To: teamgrumman-list@matronics.c
om =0A>>Sent: Monday, September 24, 2012 8:19 AM=0A>>Subject: RE: TeamGrumm
n76lima@mindspring.com=0A>>=0A>>>From: "Hosler, John" =0A>>>The OEM ran the
ground wire to the airframe with a sheet metal screw???? John=0A>>=0A>>Yes
, they did this at several locations.- The instrument lights and compass
light are grounded to the honeycomb via a ring lug on the wiring and a shee
t metal screw.=0A>>=0A>>The Magneto Ground at the ignition switch is also c
onnected to the honeycomb via the samhare, and much much=0A====0A>>
=0A>>=0A>>=0A>>=0A>>=0A>>=0A>>===========0At">http://ww
w.matronics.com/Navigator?TeamGrumman-List ========== c
s.com ========== matronics.com/contribution ===
======= =0A>st" target="_blank">http://www.matronics.com/Na
vigator?TeamGrumman-List=0Atp://forums.matronics.com=0A_blank">http://www.m
====
Message 17
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
Guess it depends on the year model. There are certainly early 70's models that
are grounding to the honeycomb just ahead of the instrument panel, by means of
a sheet metal screw. And there are other places where they did that (eyebrow
lights), so this isn't an isolated case.
I'd agree that a machine screw such as the instrument panel mount would probably
be better.
--Bob Steward
>No, they didn't. The ground from the Master goes to one of the screws that >hold
the instrument panel to the fuselage. The magneto ground should also be >going
to the instrument panel mount.
>>"Hosler, John" <JHOSLER@epri.com>
>>The OEM ran the ground wire to the airframe with a sheet metal screw????John
Message 18
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
Gary,
I have to disagree. In GA applications, you do not ground RF antenna
cables at both ends. If you review any avionics installation guide,
you'll see that they invariably caution that only one end of the cable
be grounded (the transmitter end), even if this means cutting the ground
path at the antenna end (which I always do, because even so-called
"insulated" antenna mounts often manage to conduct somehow).
The fact that COAX is unbalanced is the reason why you ground at only
one end. Balanced conductors (such as twisted pairs) have intrinsic
shielding due to an inverse of the original signal being imposed on one
conductor, creating an evenly balanced EMF (hence the term "balanced").
It relies on a sum and difference principal, where sum and difference is
the combining (summing) of two signals that are out of phase from each
other. Whatever doesn=92t cancel out is noise that can be rejected at
the receiving end.
Coax, being unbalanced, requires a shield. To function at the
frequencies present in GA aircraft, that shield has to be grounded at
only one end. As an A&P, Ham radio operator, and electrical engineer,
I've had to deal with many gnarly RFI problems. 99% of the time the
cause is double-ended grounding.
The grounding practice for aircraft shielded cables is well specified as
single-ended in almost all cases. The only exception would be RF
emitters at well above 1 GHz, in which shielded antenna cables are
grounded at both ends. These have limited application in aircraft
(mostly radar systems), but for completeness I'll explain the
difference.
Shielding effectiveness at low frequencies is a function of the
impedance of the cable shield compared to the impedance of the shielded
circuit. When grounded at both ends, not only does external RFI readily
pass through the shield, the shield itself becomes an emitter as a
result of any potential difference between the two ends of the cable --
the so-called "ground loop". One motive of grounding at one end is to
break that loop to eliminate a shield-induced magnetic field coupling
into the conductor. It doesn't make any difference if you're trying to
contain the shielded cable's signal or protect it from outside RFI.
At high frequencies, the coupling mode is via an electric rather than
magnetic field. As I mentioned earlier, we're talking here about
frequencies well above 1 GHz (so transponders, operating right at 1GHz,
aren't included). Voltage on the shield then couples to the circuit
within the cable based upon the capacitance between the shield and the
wire inside. In GA aircraft you can see this on remotely mounted radar
antennas, although most manufacturers try to put the radio right behind
the antenna to keep the cable length short. In this scenario, you want
to minimize the voltage on the shield. Terminating the shield at both
ends and at each point where the cable penetrates a bulkhead is the best
practice here, but it's seldom done on GA aircraft, due to the short
cable lengths. In large aircraft that's the recommended practice, though
(see "Aircraft and Avionics Cabling E3 Shield Termination
Recommendations,
http://www.bmpcoe.org/library/books/navso%20p-3181/53.html).
In GA, at least until we start operating microwave transmitters, the
general rule is ground at one end. Unless, of course the manufacturer
says otherwise. ;)
-mel
On Sep 24, 2012, at 12:39 PM, Gary Vogt wrote:
> Thanks Barry. That was very well said and even I understood it. I've
always wondered why both ends were grounded.
>
> From: FLYaDIVE <flyadive@gmail.com>
> To: teamgrumman-list@matronics.com
> Sent: Monday, September 24, 2012 12:18 PM
> Subject: Re: TeamGrumman-List: Re: Melted wire
>
> Mel:
>
> In response to your email... It depends on what you want to
accomplish.
>
> Example:
>
> In an RF (Radio Frequency) transmitter where there is shielding
involved you ground at both ends. An example of this would be a simple
COAX cable going to an antenna. COAX is an unbalanced medium and by
grounding at both ends (Radio & Antenna) you trap the signal and send it
to ground via the shortest path.
>
> In an AF (Audio Frequency) intercom where you want to shield a
transmitted signal such as a RF transmission, you ground the shield
(COAXIAL Shield around the twisted pair of audio lines) at one end. The
end you ground is at the intercom, which is known as The Source <-- I
know CRAZY since the source of the interference is the RF. I don't know
why they depict it that way.
>
> Think of it this way: In RF you don't want the signal to escape, you
want it to say contained within the shield. In AF you want the shield
to act as a fishing net and collect the signal and then send it to
ground. And as you said: " ... no current can be induced in a conductor
entirely at ground potential." <-- This is true in 99.9273% of cases.
Where it gets foggy is when you are talking WHAT FREQUENCY of RF and HOW
LONG A GROUND WIRE. And this stuff just starts to become a problem at
our VHF frequencies and goes really crazy at Microwave frequencies.
>
> Barry
>
>
> On Mon, Sep 24, 2012 at 2:49 PM, Mel Beckman <mel@becknet.com> wrote:
> You never ground radio-frequency interference (RFI) shields at both
ends. The objective of shielding is to absorb RFI, convert it to an
electrical current, and drain the current to ground. If you ground the
shielding at both end it won't work, because no current can be induced
in a conductor entirely at ground potential. This is true for all RFI
shielding, from ancient TV coax to the newest inter-building shielded
Category-6 data cabling.
>
> -Mel Beckman
>
> On Sep 24, 2012, at 11:40 AM, Gary Vogt <teamgrumman@yahoo.com> wrote:
>
>> on that subject, why is it (the magneto P-Lead shields) grounded at
both ends?
>>
>> From: "n76lima@mindspring.com" <n76lima@mindspring.com>
>> To: teamgrumman-list@matronics.com
>> Sent: Monday, September 24, 2012 8:19 AM
>> Subject: RE: TeamGrumman-List: Re: Melted wire
>>
>>
>> >From: "Hosler, John"
>> >The OEM ran the ground wire to the airframe with a sheet metal
screw???? John
>>
>> Yes, they did this at several locations. The instrument lights and
compass light are grounded to the honeycomb via a ring lug on the wiring
and a sheet metal screw.
>>
>> The Magneto Ground at the ignition switch is also connected to the
honeycomb via the samhare, and much much ==
>>
>>
>>
>>
>>
>>
>>
>> =========
>> t">http://www.matronics.com/Navigator?TeamGrumman-List
>> =========
>> cs.com
>> =========
>> matronics.com/contribution
>> =========
>>
>
>
> st"
target="_blank">http://www.matronics.com/Navigator?TeamGrumman-List
> tp://forums.matronics.com
> _blank">http://www.matronics.com/contribution
>
>
>
>
>
>
>
>
Message 19
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
Just for reassurance, I went out to the plane today, kicked on the master switch,
and measured .67 amps running down the 5PA3 wire that Gary recently replaced.
I used one of those wrap-around meters, which probably aren't that accurate,
but it's about the same as what Gary measured in the shop with a real ammeter.
And in the ballpark of what Bob mentioned it ought to be several posts ago
(consistent with an internal resistance in the master relay of 15 ohms). If
I understand correctly, that probably means the appropriate relay is installed
(i.e., not a starter relay).
Also, no discernible heat in said wire - as expected for that amperage.
So the only thing I have to watch for now is if there is an -intermittent- short
in the relay that only appears when I'm at 8500 feet, at night, not near any
suitable landing sites :-/
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=383940#383940
Other Matronics Email List Services
These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.
-- Please support this service by making your Contribution today! --
|