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Alt. B-Lead Routing

Jim P

Well Known Member
Is there any issue with running the alternator b-lead down the side of the engine and bundling wth the spark plug/ sensor leads, and routing back to the firewall?

Jim
 
Down the right

The Alternator is aircraft (engine fwd) right & low, so down the right side along the oil sump bolts (which can provide Adel clamp support) is the way to go for me. A clamp on the induction tube some times is handy. Some run the starter cable on left side, around the front of the engine to the right, than route it "bundled" with the b-lead and the other alternator wires, e.g., Ign/Light or Field. I personally would not bundle the b-lead with sensor or spark plug wires but you can.

Below thumbnail shows where a builder routed wires (starter/b-lead/spark plug and sensor wires) up and along the rocker covers. It looks nice; I'm sure it works well, but personally I like the low road along the sump. You do a lot of work there and it might be in the way? Just preference but I really want to minimize the length of the starter & b-lead wires. Their larger gauge and weigh a good bit. You can run the battery cable on the right solo, than around the back. The battery cable acts as a support for the smaller gauge wires if you do run it on the left, which is what I think most builders do.

WARNING: If you have constant speed prop, the metal governor tube runs down the lower right of the engine from the front bearing to the prop governor, about where you run the B-lead. Some just zip-tie the wires off the metal tube. I've seen planes with fretting and notching on the tube and frayed wire insulation who do this. Also the prop gov line can fatigue if not supported well. You don't want an electical short ever, especially a short of the B-lead on the metal prop oil-line.There has been solid oil line failures but that was when they where all aluminum. They are now stainless (on factory planes). The failures where really due to mechanics not supporting the oil line with clamps, not wires hanging of them. Still I would not use the gov line to support wires even if its stainless. Electrical arcing/welding on a high pressure oil line would not be a pretty picture. Hanging wire off metal tubes with zip-ties is bad, use padded clamps. These are the BIG wires and they on a vibrating engine. Spare no expense here.

Also the wires hanging off the back of the alternator take a good shaking. This is the source of many so called alternator problems, which often turn out to be just loose wires or broken connectors. Try to support the wires off the back of the alternator as best as you can. Wiggle those little connectors long enough they'll fail.


Here are some random related inspirational thumbnails from fellow talented RV'es and one Rocket (Randy Pflanzer last pic right)




Related topics:

Where to fuse the B-lead?
The B-lead wire usually has fuse/CB protection where it connects to the plane's main buss or at the battery but not the other way. So the if there is a short the battery and buss is protected. But what protects the wire from the power going to other way, from the alternator to the buss/battery. The wire is not protected. The good news is modern internal regulators have SHORT detection & LOSS of B-lead to battery connection logic. This logic shuts the alternator down if the b-lead shorts or opens, hopefully before it catches something on fire. Not all regulators, especially external regulators are smart enough to have short & open b-lead protection. Transpo V1200 is a good sophisticated external regulator with short/open b-lead protection as well as OV protection.

Combining the B-lead and Starter cable electrically
Some have had the idea of running the alternator B-lead to the starter and connecting it there, combining the B-lead with the starter wire into one. Electrically it can work, but I'm not too keen on that idea. If you do this, you must leave off or omit the firewall starter contactor/relay. It works and saves you a few feet of #6 wire and one relay. Leaving off the firewall relay and just using the contactor on the starter has some complications, like needing a 30 amp starter button for example. Also leaving the firewall contactor out means the starter wire is always HOT, when the master is on, ie all the time in-flight. Some are fine with that, some are not so comfortable. A firewall contactor does de-energize the battery to starter cable/wire unless the starter switch is pushed. If you don't have a real desire to be different, just follow the plans and run the discreet b-lead wire. How you route it, is up to you.
 
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Thanks George, I was looking at something along the lines of the 3rd from the left photo in the post above, but I think securing to the updraft tubes might work. I do have the stainless prop control line so that's in the way of the sump.
 
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