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E-Bus Fuse Size

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user9253

Joined: 28 Mar 2008
Posts: 1923
Location: Riley TWP Michigan

Posted: Wed Oct 31, 2018 4:35 pm Post subject: E-Bus Fuse Size

A pilot recently experienced an instrument panel blackout at night.  When he turned on the E-Bus switch, the panel briefly came back on, but soon went black again. Luckily the weather was good and he landed safely.  You can read about it here.

http://www.vansairforce.com/community/showthread.php?t=165520

The E-Bus was protected by 15 amp fuses.  Evidently the second and third owners of the aircraft connected more loads to the E-Ebus, eventually overloading it.

If two fuses are connected in series, even if one is bigger, either one or both could blow in case of hard ground fault.

 Should the E-Bus have main fuses?

If so, then how much larger should the main fuse be than a branch circuit fuse?

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Nov 01, 2018 6:20 am Post subject: E-Bus Fuse Size

At 07:35 PM 10/31/2018, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>



 A pilot recently experienced an instrument panel blackout at night. 	


     What was the failure that took down his main

     bus?



  	  Quote: 	
		    When he turned on the E-Bus switch, the panel briefly came back on, but soon went black again. Luckily the weather was good and he landed safely.  You can read about it here.

  http://www.vansairforce.com/community/showthread.php?t=165520

 The E-Bus was protected by 15 amp fuses.  Evidently the second and third owners of the aircraft connected more loads to the E-Ebus, eventually overloading it. 	


    Yup . . . ignorance is your worst enemy . . .

    sometimes the foundation for fatal mistakes.



  	  Quote: 	
		  If two fuses are connected in series, even if one is bigger, either one or both could blow in case of hard ground fault.

  Should the E-Bus have main fuses?

 If so, then how much larger should the main fuse be than a branch circuit fuse? 	


    The z-figures are too often treated as "the

    way to set up my airplane" . . . they are

    ARCHITECTURE drawings that consider options

    for minimizing risk under various failure modes.



    The values for wire and fuses are exemplar,

    not necessarily applicable to any one builder's

    project.



    The very FIRST step in planning the ship's

    final configuration is to do a LOAD ANALYSIS.

    It's real simple. The web-page at



  https://tinyurl.com/9rt6ymn



    offers two type of tools. One based on paper-

    pencil-pink-pearl technology. The other uses

    Excel. Either method gets the job done. I prefer

    the paper/pencil approach . . . it fits in the

    3-ring binder of shop notes.



    There is a form that can be downloaded from



  http://www.aeroelectric.com/PPS/Load_Analysis/Blank_Form.pdf



    You need one page for EACH bus in the aircraft.

    Just how many busses is driven by choice of

    architecture. Devices fed by those busses

    is driven by your "plan-b" analysis for dealing

    with single failures of any electro-whizzie.



    The sums of running loads for each bus are

    critical to calculating ship's endurance mode

    loads and sizing the battery to meet endurance

    mode design goals.



    These pages do another good thing. They

    are the INDEX for a page-per-system wire book.

    Each fuse/breaker on a bus gets sized, paired with

    appropriate wire and tagged as to what page

    that system's wiring details will be found.



    Once the e-bus running loads are established,

    ONLY THEN does one have sufficient information to

    size the normal and alternate feed protection.

    One COULD take the uber-conservative approach

    and wire these paths with say 10AWG wire protected

    with MAX40 fuses . . . or you can use data

    described in the load-analysis to size the

    wire/protection with at least 100% headroom

    based on running loads.



    Those are BUS feeders and need to be ROBUST with

    respect to total running loads on the bus. The

    original e-busses had typical running loads on

    the order of 3-4 amps. But as endurance mode

    support (SD-8 etc) got bigger, the constellation

    of e-bus hardware went up too.



    Had the original builder of this aircraft provided

    such information with the sale of his project,

    the future owners would at least possess information

    necessary for well crafted modifications to

    their aircraft. I've done my share of

    b*#$$n and m(#$&g about the uber-regulated

    TC aircraft environment but the hat-dance-

    of-paperwork associated with this topic

    in TC aircraft has solid foundation.



    When modifying the airplane, tho shalt

    not mess with the aerodynamics, bust

    the edges of the envelope for weight/

    balance. You will validate structural integrity

    of the installed device -AND- it's

    attach points. Lastly . . . revisit

    the electrical load analysis for validation

    of performance and FMEA.



    I'm pleased that this incident didn't have

    a sad outcome. It's a good thing that we

    learn from his experience. 



    Feel free to cross post this narrative

    to the Van's support forums.



 



 

 

   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1923
Location: Riley TWP Michigan

Posted: Thu Nov 01, 2018 9:09 am Post subject: Re: E-Bus Fuse Size

 	  Quote: 	
		  What was the failure that took down his main bus? 	


Bob, thanks for your reply.

Sorry that I did not explain the failure well.  It was not the main power bus that lost power.  It was the E-Bus.  The E-bus was wired per AeroElectric diagrams with two power inputs, one from the main bus and one from the battery.  Both inputs had 15 amp fuses.  The fuses blew because of builder error: too heavy of a load.

When two fuses are in series, what should the fuse ampacity ratio be to be sure that only the smaller fuse blows and not both?  2 to 1, or 5 to 1, or 10 to 1, or what?

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Nov 01, 2018 5:53 pm Post subject: E-Bus Fuse Size

At 12:09 PM 11/1/2018, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>



 

 > What was the failure that took down his main bus?



 Bob, thanks for your reply.

 Sorry that I did not explain the failure well.  It was not the main power bus that lost power.  It was the E-Bus.  The E-bus was wired per AeroElectric diagrams with two power inputs, one from the main bus and one from the battery.  Both inputs had 15 amp fuses.  The fuses blew because of builder error: too heavy of a load.

 When two fuses are in series, what should the fuse ampacity ratio be to be sure that only the smaller fuse blows and not both?  2 to 1, or 5 to 1, or 10 to 1, or what?



 --------

 Joe Gores

 	


  Joe, the complete answer will take a bit . . . but

  I'll get to it. In the mean time, I've been massaging

  the history of the e-bus. It is clear that the

  spirit, design goals and intent for e-bus configuration

  have evolved several generations over the past 30 years.



  I'm considering an update to the idea that removes

  all risks for not having considered the pesky details

  of fuse physics.  Let's graduate the e-bus up

  to the same design philosophy as bus structures

  in most other aircraft.



  http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z36P1.pdf

 

  The design cited above would support all practical

  e-bus loads from a LongEz to any heavy-hauler in the

  OBAM aviation world. While beefier than the Long-Ez

  needs, weight penalty is small and besides, its

  all in the nose where the canard pushers need

  the ballast anyhow.



  The bus is still crew controlled for crash safety

  and protected by a current limiter that meets the

  spirit and intent of protection for bus feeders

  while being totally immune to nuisance tripping

  by the opening of any subordinate protection.



  Next pass through the z-figures will show this

  configuration.



  Comments welcome . . .



 

   Bob . . .

rick(at)beebe.org
Guest

Posted: Thu Nov 01, 2018 5:55 pm Post subject: E-Bus Fuse Size

If two fuses are         really in series I would think the smaller one would almost         always blow first and then the second wouldn't have power on it         any more. In this incident, the fuses were really in parallel         and he actively switched from the main feed to the alt feed.         Since the load was still higher than 15 amps the second one blew         as well. Had he turned some things off before switching he         probably would have been just fine. A realization he has come         to, btw. Along with the realization that he really needs to         decipher the wiring and re-assign devices to the appropriate         buss.     

--Rick

          

     On 11/1/2018 1:09 PM, user9253 wrote:

     

      	  Quote: 	
		          	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com> (fransew(at)gmail.com)

          	  Quote: 	
		  What was the failure that took down his main bus?

	
       

Bob, thanks for your reply.

Sorry that I did not explain the failure well.  It was not the main power bus that lost power.  It was the E-Bus.  The E-bus was wired per AeroElectric diagrams with two power inputs, one from the main bus and one from the battery.  Both inputs had 15 amp fuses.  The fuses blew because of builder error: too heavy of a load.

When two fuses are in series, what should the fuse ampacity ratio be to be sure that only the smaller fuse blows and not both?  2 to 1, or 5 to 1, or 10 to 1, or what?



--------

Joe Gores





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=484227#484227

user9253

Joined: 28 Mar 2008
Posts: 1923
Location: Riley TWP Michigan

Posted: Thu Nov 01, 2018 7:11 pm Post subject: Re: E-Bus Fuse Size

What I meant by being in series are the input fuse to the E-bus and one of the E-Bus loads.  My concern is what will happen in case a load circuit shorts to ground.  For a fraction of a second, the current arcing across a fuse will exceed the fuse value.  That high arcing current could be enough to blow an upstream fuse, even if that upstream fuse has a higher current rating.  Ever notice that circuit breakers in a home service entrance panel are labeled "10K Amps" even though the breaker size is 15 or 20 amps?  The reason is that when the circuit breaker trips with a dead short, the current arcing across the opening contacts is only limited by the power company's ability to provide it.  Thus the circuit breaker is capable of withstanding very high arcing current up to 10K amps for a fraction of a second without blowing itself apart.

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Nov 01, 2018 7:24 pm Post subject: E-Bus Fuse Size

At 12:09 PM 11/1/2018, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>



 

 > What was the failure that took down his main bus?



 Bob, thanks for your reply.

 Sorry that I did not explain the failure well.  It was not the main power bus that lost power.  It was the E-Bus.  The E-bus was wired per AeroElectric diagrams with two power inputs, one from the main bus and one from the battery.  Both inputs had 15 amp fuses. 	


   The normal feed path normally doesn't

   have circuit protection. The e-bus and

   main bus should be located adjacent to

   each other and tied together through

   the back-feed prevention diode with 

   SHORT leads as shown in Z-13/8. Loss

   of bus due loss of feeder should never have

   occurred.



   The only time we need protection in the

   alternate path is when the alternate feed

   path control is a panel mounted switch.



   Wire in the alternate feed path is relatively

   small but protected with fuse that's pretty

   stiff compared to the RUNNING loads on

   the bus. I've shown 15A in most of the

   drawings but upsized to 30A in Z02.



   For the incident in question, any weakness

   in the feeder protection should have been

   rooted out with flight testing . . . an

   activity that is MANDATED for one-off

   mods in TC aircraft.



   When you have an alternate feed path

   relay, that path becomes a crew-controlled

   inter-bus feeder. With the relay located

   at the battery the feeder can be made cold

   for crash safety, then we can upsize both

   the feeder and it's protection. 

   



  	  Quote: 	
		    The fuses blew because of builder error: too heavy of a load.

 When two fuses are in series, what should the fuse ampacity ratio be to be sure that only the smaller fuse blows and not both?  2 to 1, or 5 to 1, or 10 to 1, or what? 	


   It's a bit more complicated than that. Fuses,

   indeed ALL thermally actuated protective

   devices, have an actuation time constant that

   varies inversely as the square of current.



   This is a rough figure of merit that lets

   you compare fuses of the same 'rating' but

   of different design philosophy. For example,

   a 5A "slow blow' fuse has a higher fusing

   constant than its 'fast blow' cousin of the

   same 5A rating.



   As a general rule we don't operate thermal

   devices at more than 75% of their rating

   so that pre-heating of the thermal element

   is minimized. A thermal device may stay

   closed at 80% of rating but since it's already 

   warmed up, response interval to a step rise

   in current is much faster.



   In the case of a fuse protected feeder to

   an e-bus, normal e-bus loads WILL induce

   some heating in the feeder protection thus

   pushing the fusing response down the curve.

   As I suggested earlier, operating with a

   bus feeder fuse 2x the normal running loads

   is probably sufficient but protecting with

   an extra robust (3x) or LONG time constant

   device (like a current limiter) is certainly

   an option.



   The short answer to your question is:

   The ability of upstream protection

   to hold against a downstream fault cleared

   by lighter protection is a function of

   fusing-time depression induced by pre-heating

   due to normal running loads.  You can

   size by rules of thumb but VERIFY with

   operational testing.



   It was a failure to operationally test combined

   with poorly thought out modifications to

   recommended architecture that brought

   down a nearly new LA4 and got some people

   hurt.



   See:



  http://www.aeroelectric.com/Reference_Docs/Accidents/N811HB/02_N11HB_Configuration.wmv

 

   http://www.aeroelectric.com/Reference_Docs/Accidents/N811HB/01_Fuse%20vs%20Breaker.wmv

 

  



 

 

   Bob . . .

skywagon185(at)gmail.com
Guest

Posted: Fri Nov 02, 2018 7:33 am Post subject: E-Bus Fuse Size

Joe,

 . . . didn't you mean "parallel" instead of series. . . ??



On Wed, Oct 31, 2018 at 5:40 PM user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

 

 A pilot recently experienced an instrument panel blackout at night.  When he turned on the E-Bus switch, the panel briefly came back on, but soon went black again. Luckily the weather was good and he landed safely.  You can read about it here.

 http://www.vansairforce.com/community/showthread.php?t=165520

 The E-Bus was protected by 15 amp fuses.  Evidently the second and third owners of the aircraft connected more loads to the E-Ebus, eventually overloading it.

 If two fuses are connected in series, even if one is bigger, either one or both could blow in case of hard ground fault.

  Should the E-Bus have main fuses?

 If so, then how much larger should the main fuse be than a branch circuit fuse?

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=484131#484131

 

 

 

 

 

 

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Nov 02, 2018 8:16 am Post subject: E-Bus Fuse Size

At 10:12 PM 11/1/2018, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>



 What I meant by being in series are the input fuse to the E-bus and one of the E-Bus loads.  My concern is what will happen in case a load circuit shorts to ground.  For a fraction of a second, the current arcing across a fuse will exceed the fuse value.  That high arcing current could be enough to blow an upstream fuse, even if that upstream fuse has a higher current rating.  Ever notice that circuit breakers in a home service entrance panel are labeled "10K Amps" even though the breaker size is 15 or 20 amps?  The reason is that when the circuit breaker trips with a dead short, the current arcing across the opening contacts is only limited by the power company's ability to provide it.  Thus the circuit breaker is capable of withstanding very high arcing current up to 10K amps for a fraction of a second without blowing itself apart. 	


    That's not a concern.



    Consider the ac power distribution in your house.



    A hand-held appliance may have some small protective

    device inside it . . . then you move up the chain to

    a breaker in your entry box. There may be a mains

    breaker upstream in the same box. There are probably

    fuses in the transformer behind your house. The

    neighborhood distribution system has yet more upstream

    fuses. From there on up the chain, fuses are generally

    replaced with circuit breakers all the way back to

    the power plant.



    Any one of those protective devices can be faulted

    without opening the upstream protection . . .

    IN SPITE of whatever pre-heating may be present

    due to other running loads sharing the same

    feeder.



    You can be sure that the I(squared)t fusing

    constant for every device is much greater than

    any downstream device, much less than any upstream

    device.



    The protection architecture behaves gracefully

    irrespective of the system's source impedance . . .

    which sets the maximum, instantaneous fault

    current.



    The thing that made our fuse choices more critical

    was the fact some devices were fed by upstream

    devices of the same class . . . i.e. plastic

    automotive fuses. This is not inherently a bad

    thing but it does take some careful design 

    combined with verification testing.



    I slipped up in not evolving the protection

    philosophy along with step with expanded design

    goals for the e-bus.  This placed the uninformed

    builder at risk for the 'Dark E-bus Syndrome'.



    Going foreward with Z36 should eliminate that

    risk.



 

 

   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1923
Location: Riley TWP Michigan

Posted: Fri Nov 02, 2018 9:18 am Post subject: Re: E-Bus Fuse Size

 	  Quote: 	
		  Joe,  . . . didn't you mean "parallel" instead of series. . . ?? 	


No, I meant series.  There is a fuse protecting the E-Bus and there are individual loads on the E-Bus each protected by a fuse.  The fuse for the whole E-bus and a load fuse are in series.  The fuse protecting the whole E-Bus needs to be chosen so that a hard short to ground on an individual load does not blow both the load fuse and the main E-Bus fuse.  Bob has addressed this issue with his proposed Z-36 using a MANL30 protecting a heavy duty E-Bus.  Builders keep adding more and more loads to an E-bus that was originally designed for minimum loads.

  A person I know was working on an apartment kitchen range outlet.  He stuck a screwdriver in where it should not have been and tripped not only the circuit breaker for the range, but also the main breaker for the whole building.  He had to get the apartment manager to unlock the utility room and reset the building main breaker.

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Nov 02, 2018 9:51 am Post subject: E-Bus Fuse Size

 	  Quote: 	
		    A person I know was working on an apartment kitchen range outlet.  He stuck a screwdriver in where it should not have been and tripped not only the circuit breaker for the range, but also the main breaker for the whole building.  He had to get the apartment manager to unlock the utility room and reset the building main breaker. 	


   Defective or mis-applied breaker . . . it's

   a fundamental design REQUIREMENT to prevent fault

   effects from propagating outward or upward

   in a complex system.



 

   Bob . . .

skywagon185(at)gmail.com
Guest

Posted: Fri Nov 02, 2018 12:12 pm Post subject: E-Bus Fuse Size

. . . you are certainly right; I didn't consider that you were talking about "branches". 

My email gets staged with the earlier first and I did not see your follow-up until I had already stepped on my xxx with a reply. "Must remember to read the entire thread. . .🙄 "



On Fri, Nov 2, 2018 at 10:25 AM user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

 

 

 > Joe,  . . . didn't you mean "parallel" instead of series. . . ?? 

 

 No, I meant series.  There is a fuse protecting the E-Bus and there are individual loads on the E-Bus each protected by a fuse.  The fuse for the whole E-bus and a load fuse are in series.  The fuse protecting the whole E-Bus needs to be chosen so that a hard short to ground on an individual load does not blow both the load fuse and the main E-Bus fuse.  Bob has addressed this issue with his proposed Z-36 using a MANL30 protecting a heavy duty E-Bus.  Builders keep adding more and more loads to an E-bus that was originally designed for minimum loads.

   A person I know was working on an apartment kitchen range outlet.  He stuck a screwdriver in where it should not have been and tripped not only the circuit breaker for the range, but also the main breaker for the whole building.  He had to get the apartment manager to unlock the utility room and reset the building main breaker.

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=484248#484248

 

 

 

 

 

 

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