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Wires going to CB question

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rparigoris

Joined: 24 Nov 2009
Posts: 780

Posted: Thu Jun 03, 2010 4:38 pm Post subject: Wires going to CB question

Reading "The Aeroelectric Connection" Chapter on Circuit Protection, stated is to not use the Circuit Breaker screws that mounts to bus to also connect inter-bus jumpers or main power feed lines. "These things should get their own 8-32 fasteners."



I have 2 question:

1) I have a mini e-bus on passenger headrest that will never see more than 15 amps. It consists of 3 P+B CBs. Can I feed this bus with ring terminal under the head of one of the CB screws that mounts to the bus?

2) I need to take off a wire from this e-bus that will immediately go to a 2 amp in line fuse to power my variometer, can I take power off e-bus through a ring terminal under the head of one of the CB screws that mounts to the bus?



This goes against what is stated in AC, but I am thinking perhaps it was stated considering there may be more amps than 10 or 1.



Bus bar is silver plated copper.



Thx.

Ron Parigoris

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nuckolls.bob(at)aeroelect
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Posted: Thu Jun 03, 2010 7:24 pm Post subject: Wires going to CB question

At 07:38 PM 6/3/2010, you wrote:

 	  Quote: 	
		  

<rparigor(at)suffolk.lib.ny.us>



Reading "The Aeroelectric Connection" Chapter on Circuit Protection, 

stated is to not use the Circuit Breaker screws that mounts to bus 

to also connect inter-bus jumpers or main power feed lines. "These 

things should get their own 8-32 fasteners."



I have 2 question:

1) I have a mini e-bus on passenger headrest that will never see 

more than 15 amps. It consists of 3 P+B CBs. Can I feed this bus 

with ring terminal under the head of one of the CB screws that 

mounts to the bus?

2) I need to take off a wire from this e-bus that will immediately 

go to a 2 amp in line fuse to power my variometer, can I take power 

off e-bus through a ring terminal under the head of one of the CB 

screws that mounts to the bus?



This goes against what is stated in AC, but I am thinking perhaps it 

was stated considering there may be more amps than 10 or 1.



Bus bar is silver plated copper.


	


    The idea for a bus bar is to offer contiguous electrical connection

    from some feeder to an array of tap-offs that feed breakers or

    fuses using techniques that minimize single points of failure.



    This design goal suggests that if you can stamp or otherwise

    fabricate a bus from a single piece of metal, the design goal

    is met. When the "bus" is two rows, then some means for inter

    connection the rows must be devised. Certainly, strapping

    between the rows with a similar piece of metal - each end

    enjoying a SOLID connection (solder, steel fastener with

    locking hardware, etc. then the design goal has been

    faithfully observed.



    Having said that, we can peek behind the breaker panel

    on a contemporary A36 Bonanza and see this:



http://aeroelectric.com/Pictures/Breakers/Breaker_Panel_Busing_1.jpg



http://aeroelectric.com/Pictures/Breakers/Breaker_Panel_Busing_2.jpg



     . . . here we observe specially fabricated inter-bus jumpers

     crafted from some rather robust material fitted on each

     end with equally robust flags that have been hard-soldered.



     These particular assemblies attach with the non-locking, threaded

     fasteners SHARED with the upstream side of a breaker. Hmmmm . . .

     they've been doing this for decades . . . if it's good for an

     A36 it's probably good for an RV7. But it DOES offer single

     points of multiple failures due to loosening of non-secured

     fasteners.



     So here the design goals I cited above were not observed. At the

     same time, out of many thousands of aircraft involved, we've

     probably not heard about a situation (if any) where the

     loosening of one non-locking screw affected several systems.

     I don't know the 'chefs' who crafted this recipe for success

     but the risks for adopting their philosophy is demonstrably low.



     I cannot offer a powerful argument for observing the former

     design goal over that used on the A36 except that it's not hard

     to do and has a logical rationale for implementation based on

     the same rationale that drove fabrication and assembly of the

     terminal-strip bus discussed in an earlier posting this

     evening.



     It's your kitchen . . .



     Bob . . .

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