Redundant Engine Grounds?

[Freemasm]

Probably going to regret this post. Everyone knows avionics have gotten more sophisticated and expensive. Throw EFI/EI on top of that and the cost and complexity both increase, obviously. Their integration into the powerplant and related control increase this complexity. There have been articles advocating for a second engine ground for a while now.

Redundancy can be a double edged sword. A failed engine ground would land solidly in the lower right corner of an FMEA risk (low risk/high severity); a fact that makes this an interesting question (at least to me).

So, what have owners/builders of aircraft with any/all of the aforementioned done regarding such.

 

[gasman]

1. Welding cable. 2. Braided strap.

 

[wirejock]

Grounds

One #2AWG braided strap from FOT to the engine.
One #2AWG braided strap from battery to FOT
One #6 AWG Tefzel from inside side of FOT to the Advanced Control Panel.
Any grounds not handled by the ACM are direct to the FOT except for FlyLEDs. They wre local.

I did consider a dedicated #2 Welding wire ground to the starter but in the end decided against it.

 

[PilotjohnS]

YES!

The redundancy is not so much for a hard failure, it is for the intermittent opening while it fails. An intermittent ground will send all kinds of voltage spikes through the system and probably take out all the electronics before I could react to turning off the field. I am worried more about a bolt on the braid loosening up, not a wire breaking.
It also makes the starter work that little bit less hard.

 

[bjdecker]

No!

One #2AWG (Van's ES WH-P26) wire from the case lug just behind the bottom left engine mount to the firewall as depicted in DWG OP-31, Zone D-9

The engine in my installation only has the alternator, starter, and starter solenoid as electrical devices requiring a ground/earth path. A failure of the Engine case ground will only result in the alternator inop and the starter inop; a Low Probability/Low Impact on the FMEA as I have a backup alternator, and I don't use the starter in flight

 

[gasman]

During a ground failure to the engine case, the cranking amps will find it's way to the battery by any metallic path available... Mainly throttle and mixture cable housings.

 

[Mikeyb]

For sure dual grounds decrease the probability of an engine ground failure by a factor of two, whatever that is. But there’s no way to test the two independently. It could be you are carrying a half pound of copper ballast rather than a backup ground.

The single 4 gauge welding cable on mine has a resistance including the connections of .002 ohms from the rear mounted battery to the engine case and is a more than adequate. It limits the voltage drop on the complete ground path to around 0.3 volts at 150 amps cranking.

I test it during condition inspections. It’s hard to do with a standard ohmmeter but an easy way is to do it is to connect a voltmeter between the engine and battery ground. Turn on the alternator field (3.5A) and note the voltage. If it’s less than 10 millivolts or so you are good to go. If not the voltmeter can be moved to find the location of the high resistance.