Stupid human tricks with electricity

[McFly]

I was installing a single Electonics International (EI) probe harness (the extension minus the probe) when it came in contact with the always hot buss. As advertised, the buss was hot. I did not see an arc but the harness got hot quick and smoked. The stainless shielding is discolored in places and I have some way cool stripes branded on my thumb and index finger.

I checked the harness for both continuity and for a short. I then comparied the continuity readings with a fresh harness, the numbers were identical.

Is this harness still usable?? Thanks

PS: I have been cut, sliced, burned, drilled, stabbed, bruised, pinched and blistered. I have had stuff in my eye, fiberglass rashes and a million splinters but branding is a new one for me. I'll wear it with pride.

 

[pierre smith]

Not hot

Hi Hugh,
What do you mean "always hot buss?" You should only have a hot buss when the master switch is turned on. Our hot wire to the buss bar comes from one side of the master solenoid on the firewall while the other side is connected to the battery. We have no juice in the cockpit when the master is off, with the exception of the "always hot" cigarette lighter plug. The reason for that is so we can use a solar charger plugged into the cigarette lighter to charge the battery or to charge our cellphones, etc.

 

[Tom Maxwell]

I wouldn't use it.

If you saw/smelled smoke then the insulation and probably the wire has been compromised. Although there may not be a short or an open, there could be a near burn through that will fail with continued use and/or vibration. An ohmeter uses such low current that you can't really say the wire is OK just because it ohms out OK. If it were me, I would replace the harness.

 

[McFly]

Sounds like good advice

Thanks Tom,

The more I think about it, the more I realize that I don't know what condition it's really in. Probably good enough for premature failure.

Pierre: The master will not turn off this buss (I am using the Aero Eectric Z-11 scheme). At the moment I am only using it for the single electronic ignition (I want the EI to be controled soley by the EI switch). I did have the Dynon keep alive wired to it but have since pulled the fuse and will eventually pull the wire run. Someday I may wire a cigarette plug but we'll see.

 

[Mel]

You should not have an "always hot bus" in an aircraft. The whole idea of a master switch is so you can turn off ALL electricity in case of emergency. You may have a few "hot" wires for keep alive circuits, clocks, etc. but not a complete bus.

 

[McFly]

A few wires or a small buss

You may have a few "hot" wires for keep alive circuits, clocks, etc. but not a complete bus.

You problem is not with the '"hot" buss but with the placement aft of the firewall, correct? Would an inline fuse or fuseable link installed between the buss and battery be acceptable?

I see lots of Knuckle(sp) heads use this method. What did you guys do? Thanks all.

 

[Mel]

Sorry, but I have a problem with a "hot bus" anywhere. I have a keep alive wire to my Dynon (clock) and one to my "aux" socket for my battery maintainer and that's it. When I turn off my master, I want everything dead.

 

[RV6_flyer]

Hot bus

If you look at Bob's Z-11 rev L drawing, http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdf/Z11L.pdf you will see a * on the 16 AWG wire that runs from the HOT side of the master (Battery Contactor) and the "Hot Bus" (Main Battery Bus). Looking at the notes, I find that the * = 6 inches or less. This is telling me that there is very little unprotected wire when you turn the master off. The down side is that there is a 16 AWG wire that is unprotected for 6". If it were to short out, it would get hot and carry 10 Amps till it burned out. Somewhere above the 10 amps, it would burn up like a fuse link.

The whole idea behind the master is to disconnect the battery from the rest of the airplane. Any wire that is on the hot side of the battery (or hot side of the Battery Contactor) must be a short lenght to minimize the risk if it shorts out. In the perfect world, the Battery Contactor would be bolted to the battery post. Since we do not live in a perfect world, we use a short piece of wire from the battery to the contactor.

"HOT Bus" is not the best name for this circuit. It makes it sound dangerous. Bob's words "Main Battery Bus" sounds safer. If the wire to the main battery bus fuse block is more than a few inches long (spell that as more than 1 foot), I would want to see a fuse in it at the hot side of the Battery Contactor. If the six inches of wire pass through any holes or near any metal that it could short to, I would want to see DOUBLE Insulation if it does not have a fuse protecting it. The double insulation would need inspected every condition inspection to make sure that it is not about to wear through and the wire carrying the current about ready to short out.

I have THREE (3) in line fuse holders on my airplane conected to the hot side of the battery contactor that does the same thing as Bob's "Main Battery Bus."

The purpose of the fuse or circuit breaker is to protect the wire connected to it. Our airplanes should have very little unprotected wire in them. This is the same as an automobile in that when you turn the key off (battery master off) there is little to no live circuits in the vehicle. All the circuts that are hot, should have protection againsts shorts. (fuse, CB, fuselink, battery contactor). Unfortunately we all have a few wires in the airplane that is necessary to be hot when the master is off. Many of us have Clocks, Narco radios that need voltage to remember the last frequency, Dynon, hobbs meters, courtesy light, etc. that need to have power to them all the time. All of these must be protected in some way in case the wire shorts out.

Hope this helps clarify and not create more "smoke".

I can understand where both Hugh and Mel are coming from. I am hoping that my long posts clarifies what both are saying.

(Lets see if this post gets the signature that Doug suggested we add to our profile.) Guess I can come back and edit it if it does not have a signature.