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Engine mount ground?

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rvdave

Joined: 24 Jan 2009
Posts: 191

Posted: Tue Jan 19, 2016 10:17 am Post subject: Engine mount ground?

I'm running a braided ground from firewall/forest of tabs to engine, is it necessary to ground the engine mount?

_________________
Dave Ford
Cadillac, MI

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jan 19, 2016 10:24 am Post subject: Engine mount ground?

At 12:17 PM 1/19/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "rvdave" <rv610dave(at)gmail.com>



 I'm running a braided ground from firewall/forest of tabs to engine, is it necessary to ground the engine mount? 	


   No.



 

   Bob . . .

jbsoar(at)gmail.com
Guest

Posted: Tue Jan 19, 2016 4:17 pm Post subject: Engine mount ground?

The engine mount probably doesn't require a dedicated ground strap as it is bolted to the firewall and aircraft primary structure. 



On Tue, Jan 19, 2016 at 11:17 AM, rvdave <rv610dave(at)gmail.com (rv610dave(at)gmail.com)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: "rvdave" <rv610dave(at)gmail.com (rv610dave(at)gmail.com)>

 

 I'm running a braided ground from firewall/forest of tabs to engine, is it necessary to ground the engine mount?

 

 --------

 Dave Ford

 RV6 for sale

 RV10 building

 Cadillac, MI

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=452108#452108

 

 

 

 

 

 

 

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n992dn(at)gmail.com
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Posted: Tue Jan 19, 2016 4:39 pm Post subject: Engine mount ground?

It is not necessary to ground the engine mount since it is bolted to the FW, it is however necessary to ground the engine itself, in many cases the engine is mounted to the engine mount using rubber mount, these are not great conductors.....

Nati  

On Tue, Jan 19, 2016 at 6:11 PM, John B <jbsoar(at)gmail.com (jbsoar(at)gmail.com)> wrote:

 	  Quote: 	
		  The engine mount probably doesn't require a dedicated ground strap as it is bolted to the firewall and aircraft primary structure. 



On Tue, Jan 19, 2016 at 11:17 AM, rvdave <rv610dave(at)gmail.com (rv610dave(at)gmail.com)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: "rvdave" <rv610dave(at)gmail.com (rv610dave(at)gmail.com)>

 

 I'm running a braided ground from firewall/forest of tabs to engine, is it necessary to ground the engine mount?

 

 --------

 Dave Ford

 RV6 for sale

 RV10 building

 Cadillac, MI

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=452108#452108

 

 

 

 

 

 

 

 ===========

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rvdave

Joined: 24 Jan 2009
Posts: 191

Posted: Tue Jan 19, 2016 5:22 pm Post subject: Re: Engine mount ground?

Sort of what I thought but I've been getting some feedback that there should also be a ground cable to the engine mount in case the firewall ground disconnects?  The thinking is that if the one cable disconnects the ground for alternator, starter may come through braided oil or fuel lines.  Is this valid thinking?

_________________
Dave Ford
Cadillac, MI

neal.george(at)gmail.com
Guest

Posted: Tue Jan 19, 2016 5:39 pm Post subject: Engine mount ground?

 	  Quote: 	
		   On Jan 19, 2016, at 6:34 PM, Nati Niv <n992dn(at)gmail.com> wrote:

 

 It is not necessary to ground the engine mount since it is bolted to the FW, it is however necessary to ground the engine itself, in many cases the engine is mounted to the engine mount using rubber mount, these are not great conductors.....

 

 Nati  


	


Engine mounts should never be used as a ground path.  Strap the crankcase to the ground post.  No excuses. 



Even though the bolts and bushings that pass thru the rubber components will ohm out and indicate continuity, carrying electrical loads is not part of their job description.  Many relatively recent aircraft designs incorporate bonding straps bolted to either side of the vibration isolator and to the crankcase specifically to keep current out of the mounting points.  



Steel is a relatively poor conductor. Joints make it worse by inserting resistance.  High current passed thru a resistive path makes heat, which accelerates the chemical reaction that we describe as corrosion.  Add insidious Galvanic corrosion due to dissimilar metals in constant contact. 



Apart from that, assuming one removes the paint from the mating surfaces, the 4130-steel engine mount bolted to the stainless or galvanized firewall makes a poor ground when new and an awful ground as corrosion forms over time.  



And it will corrode, despite application of DC 4, Par-al-ketone, ACF-50, (etc., pick your favorite goop)...



Neal

jbsoar(at)gmail.com
Guest

Posted: Tue Jan 19, 2016 5:39 pm Post subject: Engine mount ground?

Yes, it is valid thinking.  You want a good ground, that is mechanically sound.  It goes from the crankcase to the firewall ground.  You can include the engine mount if you wish.  Does the engine mount have a convenient ground tab?  If it does, then run another ground strap to your firewall ground.  This won't weigh much, or cost much.  (Belt and suspenders, so to speak.)Bob Nuckolls writes about this in the manual.  A good read!

On Tue, Jan 19, 2016 at 6:22 PM, rvdave <rv610dave(at)gmail.com (rv610dave(at)gmail.com)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: "rvdave" <rv610dave(at)gmail.com (rv610dave(at)gmail.com)>

 

 Sort of what I thought but I've been getting some feedback that there should also be a ground cable to the engine mount in case the firewall ground disconnects?  The thinking is that if the one cable disconnects the ground for alternator, starter may come through braided oil or fuel lines.  Is this valid thinking?

 

 --------

 Dave Ford

 RV6 for sale

 RV10 building

 Cadillac, MI

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=452119#452119

 

 

 

 

 

 

 

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 r> > w.buildersbooks.com" rel="noreferrer" target="_blank">www.buildersbooks.com

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 ===========

  -

 Electric-List" rel="noreferrer" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List

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 eferrer" target="_blank">http://forums.matronics.com

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user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Tue Jan 19, 2016 8:11 pm Post subject: Re: Engine mount ground?

Yes, it is valid thinking.  But it is not necessary or even desired to ground the engine mount.  It will not hurt anything if the engine mount is grounded.  But if a backup ground path is wanted, then run a second ground strap from the engine block to the firewall.

_________________
Joe Gores

glastar(at)gmx.net
Guest

Posted: Wed Jan 20, 2016 2:05 am Post subject: Engine mount ground?

taking a different path is valid thinking (ask me how I know!!)

But then I rather would prefer to have a 2nd strap as backup as 

otherwise you would need a bridge strap at the rubbermounts.



Cheers Werner



On 20.01.2016 02:22, rvdave wrote:

 	  Quote: 	
		   



 Sort of what I thought but I've been getting some feedback that there should also be a ground cable to the engine mount in case the firewall ground disconnects?

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 20, 2016 7:48 am Post subject: Engine mount ground?

At 04:03 AM 1/20/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: Werner Schneider <glastar(at)gmx.net>



 taking a different path is valid thinking (ask me how I know!!)

 But then I rather would prefer to have a 2nd strap as backup as otherwise you would need a bridge strap at the rubbermounts. 	


   As Neal pointed out earlier . . . and I have asserted

   many times over the years, engine mounts are for holding

   engines onto airplanes. They should not be pressed into

   service as any part of the electrical system . . . voltages

   impressed across structural joints due to large circulating

   currents exacerbates corrosion. Not that this is a

   demonstrated hazard but diligent failure mode effects

   analysis dictates that using the engine mount as part of

   the electrical system is simply not necessary and elevates

   an otherwise zero-risk to some non-zero number.



   Another point of interest is the risk for 'burning ship's

   wiring' with starter currents should a firewall-to-crankcase

   bond strap become unhooked. Throughout the 'Connection and

   here on the List, builders have been cautioned about having

   ANY pathway grounded in two places on the airplane . . .

   with p-lead shields being the most common violation of that

   philosophy. Multiple grounds for engine instrumentation run

   a close second. These are 'ground loops by design', easy

   (and sometimes important) to avoid.



   Lastly, the firewall-to-crankcase bond strap should be

   as "reliable as prop bolts". The only incident for loss

   of crankcase grounding I witnessed was a mechanic's slip-

   up on one of our airplanes at K1K1 . . . and yeah, it

   burned the p-lead shields wired per Cessna factory

   drawings.  I recommend an flat braid strap from some

   structural bold on engine to the firewall ground stud.

   Alternatively, a 2AWG piece of WELDING CABLE with lugs

   installed per 



  http://tinyurl.com/gm8lqxo 



   . . . and attached with robust hardware will give

   your prop bolts a serious challenge in the longevity/

   reliability race.



 



 

 

   Bob . . .

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