Question on wire diameter and circuit breaker size Z11 schematic

[William]

Hello everyone I'm in the middle of wiring my RV6A and see what appears to be a discripency on the Z11 schematic. I will be running 3 busses. A main battery bus, EBUS, and a main power distribution bus. My EBUS and Main battery distribution bus both have approximately 30amps worth of cirucuit breakers. The main battery bus is a fuse block mounted on the engine side of the firewall. The battery contacter to the main battery bus is a 16awg wire, but it is only allowed to be 6 inches long. I plan on putting the battery bus fuse block on the engine side of the firewall to keep this 6 inch rule. My first concern is how the engine heat is going to effect the plastic fuse block? Next concern is the Z11 schematic shows a 7amp EBUS fuse on the main battery bus, but the ebus has 34amps worth of circuit breakers being utilized off of it, is the 7amp ebus fuse on the main battery bus is a misprint? Lastly since my ebus will be mounted on the panel in the form of circuit breakers connected with bus bar the power wire running from the main battery bus to the ebus needs to be more then 16awg, but the shcematic dictates different, another misprint? Should this wire not be 6awg just like the main power distribution bus?


thanks all,
Bill

[pa38112]

The EBus web site has an excelent document on wire and fuse sizes. I would read that, and it will answer all of your questions. I think it is on the "Downloads" page.

[William]

Originally Posted by pa38112

The EBus web site has an excelent document on wire and fuse sizes. I would read that, and it will answer all of your questions. I think it is on the "Downloads" page.

Pa38112 I'm not familiar with the EBus web site. Do you have a link?


thanks,
Bill

[AME at Large]

The info you are looking for and the one alluded to I believe, is the AeroElectric Connection. It's a big site with lots of wiring info and a book of the same name on the subject. See here; http://www.aeroelectric.com/
The most important part of the book in my opinion is the Appendix in the back. That is where you will find the drawings like the Z11 and several others but be sure to read the notes on the drawings first, lots of good info there. AC43.13 has a good wiring section as well.
As for your questions, I would not mount a plastic fuse block on the engine side of the firewall, but that is just me. Others may have more experience in the matter.
There is a difference between the actual load of the device and the rating of the circuit breaker/fuse used to protect it. For instance an electric turn and bank is fused at 1 amp but only draws 0.25 amps while running (more at start up). So your concern of having 30 amps worth of circuit breakers is perhaps not an accurate assessment of the real current the supply wire will see, the actual load may be less.
The 7 Amp fuse for the Ebus on the Z11 drawing is not a mistake. The drawings are meant as a guide, you are free to modify and use them as your situation and mission profile dictate. Keep in mind the Ebus alternate feed diode can only handle so much current as well.
The wire size shown on the drawing is a guide as well, probably not a mistake there either. The amount of stuff connected to the bus (main as well as Ebus) dictates the wire size. If you load up on the Ebus the wire used to supply it must be sized to handle the current. Check AC43.13 for the wire size chart. Have you done an electrical load analysis for the equipment you plan to install? Of course the installed equipment has an effect on the wiring, are you IFR or VFR, electronic ignition or mags?
Do you really need a hot battery bus? I've wired a friends plane with only an Ebus and a Main Bus and it works fine, simple is better. It's fused with an inline 10 amp fuse at the battery, wired with 14 gauge wire and the Ebus circuit breakers are on the panel next to the main bus ones.
Hope this helps.
Phil

[William]

Originally Posted by AME at Large

The info you are looking for and the one alluded to I believe, is the AeroElectric Connection. It's a big site with lots of wiring info and a book of the same name on the subject. See here; http://www.aeroelectric.com/
The most important part of the book in my opinion is the Appendix in the back. That is where you will find the drawings like the Z11 and several others but be sure to read the notes on the drawings first, lots of good info there. AC43.13 has a good wiring section as well.
As for your questions, I would not mount a plastic fuse block on the engine side of the firewall, but that is just me. Others may have more experience in the matter.
There is a difference between the actual load of the device and the rating of the circuit breaker/fuse used to protect it. For instance an electric turn and bank is fused at 1 amp but only draws 0.25 amps while running (more at start up). So your concern of having 30 amps worth of circuit breakers is perhaps not an accurate assessment of the real current the supply wire will see, the actual load may be less.
The 7 Amp fuse for the Ebus on the Z11 drawing is not a mistake. The drawings are meant as a guide, you are free to modify and use them as your situation and mission profile dictate. Keep in mind the Ebus alternate feed diode can only handle so much current as well.
The wire size shown on the drawing is a guide as well, probably not a mistake there either. The amount of stuff connected to the bus (main as well as Ebus) dictates the wire size. If you load up on the Ebus the wire used to supply it must be sized to handle the current. Check AC43.13 for the wire size chart. Have you done an electrical load analysis for the equipment you plan to install? Of course the installed equipment has an effect on the wiring, are you IFR or VFR, electronic ignition or mags?
Do you really need a hot battery bus? I've wired a friends plane with only an Ebus and a Main Bus and it works fine, simple is better. It's fused with an inline 10 amp fuse at the battery, wired with 14 gauge wire and the Ebus circuit breakers are on the panel next to the main bus ones.
Hope this helps.
Phil

Hi Phil thanks for the response. I'm currently setup for day/night vfr with mags, but plan on adding one electronic ignition in the near future which is why I was leaning towards the battery bus. You got my attention with by passing the battery bus and wiring the ebus directly off of the battery with a inline fuse, but I'm concerned about a dead battery if I forget to turn off one of the items on the ebus. Has this been a issue for your friends plane?

thanks,
Bill

[AME at Large]

It's not really an issue. The Ebus is only directly powered from the battery when the Alternate Feed switch is on. In normal operation it gets it's power through the Ebus diode and the switch is off.
Even if it was left on there is ample indication that the switch is on as the items on the Ebus include the pitch trim with LED indicator, turn and bank, EIS instrument and Comm 1.
Adding a wire or a circuit for electronic ignition while in the planning stages is always a good idea.
The architecture of the Ebus is similar to a dual fed bus like on larger planes. Lots of them have two means of powering critical electrical system stuff with diode isolation. Usually power sources are a main and standby generator but using the alternator and battery on a small plane will suffice. It's still better than most Cessna, Piper, Beech spamcans.
Phil

[az_gila]

If you have 37 amps of breakers on the E-Bus, perhaps there are too many items on it?

My theory is that only items needed to safely go to the next airport are needed in a worse case flight mode - in your case night VFR.

[tim2542]

Originally Posted by az_gila

If you have 37 amps of breakers on the E-Bus, perhaps there are too many items on it?

My theory is that only items needed to safely go to the next airport are needed in a worse case flight mode - in your case night VFR.

Assuming for the moment your are building an "E"ndurance Bus 'ala Bob Knuckles, you may have missed the point of having one. Like Gil said, it's for the bare essentials you need to get you on the ground safely. Something like 6-8 amps max, I think, is what Bob is talking about. The idea being to budget the electrical load vs. the amps available in a healthy fully charged battery, to match the fuel endurance.
I'm not saying you can't do it other ways, but I believe that's philosophy behind it, shed the load by shutting off the master and turning on the Ebus.
Tim

[William]

Thanks Gil and Tim; I do understand the reasoning behind the EBus. I guess I was a little over estimating the current I plan on using it for. I plan on putting my efis, com, and transponder on the Ebus. My concern is on the Z11 schematic the fuse on the Battery bus for the Ebus is only 7amps yet the shcematic also shows over 30amps worth of fuses being used off the Ebus. Why is this?

thanks,
Bill

[William]