Engine mount to terminal clearance

crabandy · #1 03-05-2013, 11:44 AM

It's not what I envisioned when I put the anl/shunt on the firewall, but before I make anymore wires I wanted to check with VAF. The anl/ shunt is on the right (copilot) side of the firewall about halfway top to bottom. The top nut of the shunt is 1/8 inch from the engine mount tube. The wires and terminals 1/4 inch away.

I was going to put a rubber boot on it and no amount of firewall flexing will make it touch. In a crash it could bend and touch but the master and alt should cut power. Is it too close and I should move it or it is fine and build on?

JonJay · #2 03-05-2013, 01:07 PM

AC43-13-1b Chapter 11 calls out terminal blocks or studs to have "adequate" clearance from structure. It does not say what "adequate" clearance is. AC43 goes on to say, if there is not "adequate" clearance, you can place an insulator between the terminal and structure.

The only risk I see to the way you have it is if the terminal loosened and rotated against the engine mount. If you place an insulator there, that risk would go away.

Sorry, but that is the best I can do. Perhaps a few stronger opinions will chime in.

crabandy · #3 03-06-2013, 09:36 PM

I decided to adjust the shunt, I filled the previous hole with rivets for a doubler plate. It was a little too close for my comfort, I'll feel better after I get a little more accomplished.

Walt · #4 03-07-2013, 06:02 AM

I'd use a MS21042 nut to provide for a little more clearance and a boot on the terminal. I'd also use some loctite to be sure that sucker doesn't come loose!

Rupester · #5 03-07-2013, 08:37 AM

Although it's not worth a plug nickel, I'm feeling more comfortable with the added clearance you elected.

That was awfully close before.

jjconstant · #6 03-07-2013, 09:10 AM

The thing I like most about your solution is that YOU were wondering if it was too close and YOU decided for your peace of mind to change it to something you were more comfortable with. I have often found that running a potential problem by people, either online or in person, helps me most by telling me that I'M not comfortable. It's great to get the feedback, but the biggest help sometimes is the sounding-board effect of hearing myself ask the question. That helps me decide to go to the trouble of changing things.

JonJay · #7 03-07-2013, 09:50 AM

I agree totally with Jeremy's comments and I have been in that boat before. Also, sometimes we ask questions in the hope of getting a favorable answer, but you took it upon yourself to do what you feel is right. There are a lot of those decisions to be made in a build.

I look to published resources first, AC43, maintenance manuals, etc... but, just like this, there are many things that are not black and white.

Way to move on and keep your build going.

crabandy · #8 03-07-2013, 02:54 PM

Jeremy and JonJay pretty much summed it up. Thanks for everyones replies, on another note I've almost completed the FWF (-engine moniter harness) and I got my first wire through the firewall!

TangoPapa · #9 03-07-2013, 06:03 PM

Quote:

Originally Posted by crabandy

I decided to adjust the shunt, I filled the previous hole with rivets for a doubler plate. It was a little too close for my comfort, I'll feel better after I get a little more accomplished.

Flip the shunt to the bottom post. there is plenty of room down at that end.

crabandy · #10 03-07-2013, 06:56 PM

TangoPapa,
The vertical orientation of the shunt was a tad close to the engine mount, (pics) I moved it to the side and horizontally and now have plenty of space. Moving it to the bottom post would have also worked, but I would've had to make another Alt B lead to reach the upper post.
Seems like I'm at the point that I've got to make some mistakes or I'll never get anything done.