always hot wires
Where is that EFI bus located?
Bob Nuckols' Aeroelectric Connection: "As a rule of thumb we try to avoid long runs of always hot wire fused at more than 7A. This is a crash-safety issue. If your E-Bus really needs a feeder protected at more than 7A, consider adding a power relay..." (rev 12A says in Appendix Z Page Z-6 under Figure Z-32)
In the Aeroelectric List I found: "Always hot wires are either crew controlled (relay or contactor) -OR- protected at low levels on the order of 7A fuse or 5A breaker. If you are attaching wires to the battery and they have lengths greater than the 6-inch rule of thumb then the design goal for low magnitude protection applies. In other words, a battery bus is located next to the battery. Any other location makes it something else."
Also an always hot wire can get you in trouble while working on the aircraft if you don't disconnect the negative battery terminal first.
The S704-1 20A relay sold by B&C has coil current of only 0.1A.
Bob Nuclols puts a "current limiter" in the alternator B lead so if there is a hard short at the alternator the current limiter will open. A fat wire shorted to aluminum sheetmetal will reportedly clear itself by burning the aluminum away like EDM machining but shorted to something thicker like alternator or engine case can conduct hundreds of amps. http://www.aeroelectric.com/articles/anl/anlvsjjs.html
Note also that Bob adds a starter contactor close to the battery contactor so there will not be an always-hot fat wire running to the starter.
Just my 2 cents as a Nuckols believer... flame on!
... I have been considering running an AWG 6 "fat wire" to the switches for the EFI bus. According to Nuckolls he feels it does not require fusing.
Where is that EFI bus located?
Bob Nuckols' Aeroelectric Connection: "As a rule of thumb we try to avoid long runs of always hot wire fused at more than 7A. This is a crash-safety issue. If your E-Bus really needs a feeder protected at more than 7A, consider adding a power relay..." (rev 12A says in Appendix Z Page Z-6 under Figure Z-32)
In the Aeroelectric List I found: "Always hot wires are either crew controlled (relay or contactor) -OR- protected at low levels on the order of 7A fuse or 5A breaker. If you are attaching wires to the battery and they have lengths greater than the 6-inch rule of thumb then the design goal for low magnitude protection applies. In other words, a battery bus is located next to the battery. Any other location makes it something else."
Also an always hot wire can get you in trouble while working on the aircraft if you don't disconnect the negative battery terminal first.
The S704-1 20A relay sold by B&C has coil current of only 0.1A.
Bob Nuclols puts a "current limiter" in the alternator B lead so if there is a hard short at the alternator the current limiter will open. A fat wire shorted to aluminum sheetmetal will reportedly clear itself by burning the aluminum away like EDM machining but shorted to something thicker like alternator or engine case can conduct hundreds of amps. http://www.aeroelectric.com/articles/anl/anlvsjjs.html
Note also that Bob adds a starter contactor close to the battery contactor so there will not be an always-hot fat wire running to the starter.
Just my 2 cents as a Nuckols believer... flame on!
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