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.