Matronics Email Lists :: View topic - EBUS Circuit Protection

Matronics Email Lists
Web Forum Interface to the Matronics Email Lists

Get Email Distribution Too! FAQ Search Memberlist Usergroups Register

Profile Log in to check your private messages Log in

EBUS Circuit Protection

Matronics Email Lists Forum Index -> AeroElectric-List

View previous topic :: View next topic

Author Message

paul.zimmer00(at)gmail.co
Guest

Posted: Sun Nov 11, 2012 5:57 pm Post subject: EBUS Circuit Protection

I didn't include circuit protection for my EBUS, that is powered through a B&C Essential bus diode.  The best explanation for not doing so is that it seemed unnecessary at the time I was designing the electrical system, and protection was not called for in the Z-12 drawing after which my electrical system in based.  I am second guessing myself now, especially given the documentation that comes with the EBUS diode shows a breaker (not to exceed 25A).  

  

As far as I can reason, the only purpose for circuit protection would be to protect the diode itself.  If the diode was not present and the bus bar that is the EBUS was simply an extension of the Main bus, circuit protection between the bus bars would not be called for.

  

Would you recommend adding circuit protection between EBUS and main bus?  Will the Essential Bus Diode open if its current rating is sufficiently exceeded, or will it allow current to pass (albeit in both directions)?  It seems that circuit protection would be a good thing since you would have no good way to tell if the diode had been compromised (unless of course it opened after being sufficiently abused). 

  

Thanks in advance for your help.

 

Paul 

 

  [quote][b]

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Nov 12, 2012 7:25 am Post subject: EBUS Circuit Protection

At 07:55 PM 11/11/2012, you wrote:

I didn't include circuit protection for my EBUS, that is powered 

through a B&C Essential bus diode.  The best explanation for not 

doing so is that it seemed unnecessary at the time I was designing 

the electrical system, and protection was not called for in the Z-12 

drawing after which my electrical system in based.  I am second 

guessing myself now, especially given the documentation that comes 

with the EBUS diode shows a breaker (not to exceed 25A).



As far as I can reason, the only purpose for circuit protection would 

be to protect the diode itself.  If the diode was not present and the 

bus bar that is the EBUS was simply an extension of the Main bus, 

circuit protection between the bus bars would not be called for.



Would you recommend adding circuit protection between EBUS and main 

bus?  Will the Essential Bus Diode open if its current rating is 

sufficiently exceeded, or will it allow current to pass (albeit in 

both directions)?  It seems that circuit protection would be a good 

thing since you would have no good way to tell if the diode had been 

compromised (unless of course it opened after being sufficiently abused).



Thanks in advance for your help.



    The legacy philosophy for circuit protection

    in airplanes says fuses and breakers are to prevent

    fire/smoke from wires. That doesn't mean that some

    system designer/integrator might deduce

    an alternate or supplemental requirement for

    a particular style and placement of protection.

    An example would be the use of a circuit breaker upstream

    of a crowbar ov module where the breaker not only

    protects wires, it's a component of a rapid response

    disconnect for alternator field power.



    In light of these assertions, the need for wire

    protection in the e-bus normal feed path is

    predicated on lengths of wires. The legacy philosophy

    for leaving protection out is predicated on a length

    of the at-risk path. The rule of thumb which guided

    such decisions at my places of employment was that

    path length of 6" or less does not require protection.



    It has always been my assumption that an e-bus and

    main bus structure would be located very close to

    each other and the diode wires were short.

    Perhaps I should have put the "6 inches or less"

    flag (*) on those wires.



    Power diodes almost always fail shorted. An easy

    test during pre-flight is to close the alternate

    feed path switch to power up for getting your ATIS

    or clearance delivery . . . or just to test the

    alternate path switch. If the diode is shorted, the

    whole panel will light up  . . . not just e-bus

    appliances.



    I've seen diodes fail open, but never in the passive

    sense that would tend to hide their condition from

    external inspection. These diodes literally exploded

    leaving two wire stubs waving in the breeze. The

    fat diode used for the normal feed path isolation

    is not likely to fail with such fanfare . . . which

    leaves shorting as the only, easily tested risk.



    The short answer to your question is "no" assuming

    the wires are short.



   Bob . . .

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

Display posts from previous:

	Matronics Email Lists Forum Index -> AeroElectric-List	All times are GMT - 8 Hours
Page 1 of 1

Jump to:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum