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Long and short hot feeders

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jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Tue Jun 01, 2010 9:36 am Post subject: Long and short hot feeders

I have used Littlefuse modular fuse holders to make up a fuse panel. This presents the problem of all the fuse holders having a short 6-10" wire to reach the bus. 



Are they short enough to ignore (like the * denoted wires in the Z-figures) or are fuselinks appropriate here?

I also want to bring the battery bus up close to the fuse panel so that the batt bus fuses can be displayed in the panel. The # 12-14 hot feeder wire is about 24". Putting a mini-contactor at the battery end seems to defeat the purpose of the always-hot  batt bus, but from previous kicks in my rear, I'm hesitant to say "fuselink" here. 



But I guess I can't help myself!



I'm confused about where fuselinks are appropriate and where they aren't. It seems like a hot feeder is an appropriate place because I want the feeder hot and be able to handle inrushes without interruption. But if there's a dead short on it I want it to fail before all the arcing sets something on fire or melts adjacent infrastructure.

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jun 01, 2010 11:02 am Post subject: Long and short hot feeders

At 12:36 PM 6/1/2010, you wrote:

 	  Quote: 	
		  



I have used Littlefuse modular fuse holders to make up a fuse panel. 

This presents the problem of all the fuse holders having a short 

6-10" wire to reach the bus.


	


   Why so long?



 	  Quote: 	
		  Are they short enough to ignore (like the * denoted wires in the 

Z-figures) or are fuselinks appropriate here?

I also want to bring the battery bus up close to the fuse panel so 

that the batt bus fuses can be displayed in the panel. The # 12-14 

hot feeder wire is about 24". Putting a mini-contactor at the 

battery end seems to defeat the purpose of the always-hot  batt bus, 

but from previous kicks in my rear, I'm hesitant to say "fuselink" here.



But I guess I can't help myself!



I'm confused about where fuselinks are appropriate and where they 

aren't. It seems like a hot feeder is an appropriate place because I 

want the feeder hot and be able to handle inrushes without 

interruption. But if there's a dead short on it I want it to fail 

before all the arcing sets something on fire or melts adjacent infrastructure.


	


   Fusible links are recommended ONLY where depicted

   on the z-figures. Check the archives for lots

   of discussion.



   I'm mystified as to the value in building a distribution

   component that has so many crafted joints and detail

   parts. Off-the-shelf fuse blocks were originally proposed

   for their cost of ownership savings over the legacy

   breaker panel configurations.



   But it seems you're driving your parts count up

   markedly along with $time$ invested to construct

   and maintain it.

   Bob . . .

jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Tue Jun 01, 2010 1:29 pm Post subject: Re: Long and short hot feeders

Bob,



Re length:

That's how far away my fuse panel is from the buss. Understand that the modular fuseholders are single fuse holders that you can clip together to make any size fuseholder you desire. You can fit more fuses in the same space as the off-the-shelf blocks.



see http://www.littelfuse.com/data/en/Data_Sheets/155_153PCMount.pdf 



They allowed me to fit all my fuses into available space. I wanted to be able to see the panel because I intend to use the ATO fuses with a blown indicator light.



So yes, there are two additional crafted connections on the  pigtail to the bus. And yes it's a lot more work to make a panel to accomodate the modular system. And yes, the modular cost savings over a pre-configured plug'n play panel is negligible. And yes none of this makes any sense, except that I like the look of the panel that I made.

  

So would fusible links be appropriate for the pigtails?

jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Tue Jun 01, 2010 2:08 pm Post subject: Re: Long and short hot feeders

Bob,



In your FAQ on the AC, you say:

"Fusible links are used when you have a

single leadwire to protect where it is VERY unlikely that it will ever see a serious fault and/or

where the

ultimate in circuit reliablity is needed."



Additionaly you speak of using fusible links to "extend the bus..."



It seems that running a wire from the battery to a remote battery buss meets the fusible link appropriate useage you've discussed. But your caveat about not adding fusible links to Z-figures gives me pause. I'm not comfortable second guessing your expertise.



John

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jun 01, 2010 3:37 pm Post subject: Long and short hot feeders

At 05:08 PM 6/1/2010, you wrote:

 	  Quote: 	
		  



Bob,



In your FAQ on the AC, you say:

"Fusible links are used when you have a

single leadwire to protect where it is VERY unlikely that it will 

ever see a serious fault and/or

where the

ultimate in circuit reliablity is needed."


	


    Yes. In this regard, they are very much like

    the ANL current limiters. Exceedingly robust

    but weak link in the electron chain . . .

 	  Quote: 	
		  Additionaly you speak of using fusible links to "extend the bus..."


	


   but ONLY in the configuration depicted. This

   is a special case for using a circuit breaker

   upstream of a crowbar ov module when the bus

   is a distribution point for fuses. If the

   crowbar module is installed in an aircraft

   with a classic breaker panel, then the "extended"

   bus is not needed and the breaker gets installed

   right next to its brothers and sisters.



   If you have an array of fuses or breakers used

   to distribute power in the aircraft, then the

   BUS is located right at the upstream side of

   that fuse or breaker. This is how you get the low

   parts count and compact assembly. We don't

   bring an array of wires off a bus to fuse(s)

   or breaker(s) and  hence to the protected loads.



   If you're going to assemble your own fuse block,

   then what you've proposed will FUNCTION as

   advertised . . . but it's not something that

   anyone in the business would recommend.



 	  Quote: 	
		  It seems that running a wire from the battery to a remote battery 

buss meets the fusible link appropriate useage you've discussed.


	


    Absolutely not. Always hot wires are either

    crew controlled -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.



 	  Quote: 	
		    But your caveat about not adding fusible links to Z-figures gives 

 me pause. I'm not comfortable second guessing your expertise.


	


   The wires you propose are simply wires. There is

   no useful purpose in calling them or designing them

   to be "fusible links".  Wire it up and it WILL

   function.

   Bob . . .

jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Tue Jun 01, 2010 9:43 pm Post subject: Re: Long and short hot feeders

Aargh! 

I hate arguing with common sense and good design when I've spent all that time making that cute little panel. 



But your reasoning is hard to refute.



Honestly I got so caught up in making this cool fuse panel and getting 30 fuses in a tight pattern that I overlooked the fact that I was going to have a whole nest of hot wires to deal with.



Just have to get used to not being able to see my fuses and comfort myself with fewer parts count and fewer constructed joints. And ditto on the battery bus. It's moving back to the battery.



Again thanks for taking the time to explain all this. I makes it a little easier to throw that fuse panel into the trash.



John

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jun 02, 2010 7:33 am Post subject: Long and short hot feeders

At 12:43 AM 6/2/2010, you wrote:




Aargh!



I hate arguing with common sense and good design when I've spent all 

that time making that cute little panel.



But your reasoning is hard to refute.



Honestly I got so caught up in making this cool fuse panel and 

getting 30 fuses in a tight pattern that I overlooked the fact that I 

was going to have a whole nest of hot wires to deal with.



Just have to get used to not being able to see my fuses and comfort 

myself with fewer parts count and fewer constructed joints. And ditto 

on the battery bus. It's moving back to the battery.



Again thanks for taking the time to explain all this. I makes it a 

little easier to throw that fuse panel into the trash.



    You're not alone. EVERY finely tuned recipe for success was

    preceded by many if not thousands of experiments that were

    discarded.



    Thomas Edison was often referred to as the "master experimenter"

    in recognition of his patience and persistence in the conduct

    of his craft. Charles Kettering, ditto.



    I cannot begin to deduce the magnitude of my own efforts that

    that ultimately went into the trash . . . the reason being

    that those experiences were discarded both physically and

    intellectually. But when the effort was successful, the

    work product went into useful service and the recipe for

    success went into the intellectual archives for future

    reference.



    I recall visiting an estate sale about 20 years ago that

    included a lot of goodies from a ham radio operator that

    had departed this earthly plane. While digging through a pile

    of stuff, I was startled to see a familiar device. It was

    a vacuum tube electronic code keyer that I built for another

    ham perhaps 25 years earlier . . . I don't know how many times

    it changed hands but it was still functional. Further, I

    could still draw a schematic for the thing.



    Good education is NEVER inexpensive in terms of $time$

    and slips to schedule. But it seems to me that the most

    "expensive" lessons are best retained. By having

    this discussion on the List, we're reducing the investment

    necessary for others to benefit from simple-ideas

    that go into their own exploitation of the same recipe for

    success. If it's any consolation, your loss contributes

    to the gains of others . . . but only if it's shared.



    I've often remarked to publishers of my articles that

    they solicit articles on failures too. I always get a

    reaction of surprise and perhaps dismay. I then explain

    that it's often more useful to know what does not work

    as things that do work. It's a prophylactic against repeating

    the same failure over and over again.



    Keep at it my friend and thanks for participating.



    Bob . . .

rckol

Joined: 14 Nov 2008
Posts: 36

Posted: Thu Jun 03, 2010 1:21 pm Post subject: Re: Long and short hot feeders

John,



It looks like you are going to change course here based on Bob's advice, so this information may not be needed but, I noticed yesterday that SteinAir is selling bus bar/terminal strips with 10 terminals each on them that could probably be used to feed your fuse holders, if they were located in close proximity to your fuse holders.



http://www.steinair.com/strips.htm

_________________
rck

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jun 03, 2010 5:50 pm Post subject: Long and short hot feeders

At 04:21 PM 6/3/2010, you wrote:

 	  Quote: 	
		  



John,



It looks like you are going to change course here based on Bob's 

advice, so this information may not be needed but, I noticed 

yesterday that SteinAir is selling bus bar/terminal strips with 10 

terminals each on them that could probably be used to feed your fuse 

holders, if they were located in close proximity to your fuse holders.



http://www.steinair.com/strips.htm


	


    Hmmmm . . . I cannot imagine where those would

    be used. Further, they feature non-locking, threaded

    fasteners.



    When such devices are called for in TC aircraft (rarely)

    they look more like this . . .



http://aeroelectric.com/Pictures/Wiring_Technique/Terminal_Strip_Captive_Stud.jpg



    Note the captive treaded studs with LOCKING hardware.

    I need to go back and look up that installation in the wire

    books. In the picture above we see a mix of wire guages

    which makes me wonder if it's a ground bus. Otherwise,

    one would be hard pressed to provide appropriate

    fuse/breaker protection for the wires serviced by

    the bus.



    In any case, if one truly needs such a bus, then

    drill and tap a copper bar for at least 8-32 (10-32

    better) screws. Thread in from back side and captivate

    screws to bus bar with JB weld under head of screws

    and last few threads under head. Torque well.



    Terminal faces on wires go right against the bar and

    against each other on the stud side. Cap of with a flat

    washer and well torqued locking nut. If you need to

    insulate the assembly from ground, then some work on

    a saw and drill press will carve out a piece of

    phenolic, delrin, lexan or perhaps even some cutting board

    stock.



    Bob . . .

jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Fri Jun 04, 2010 7:49 am Post subject: Re: Long and short hot feeders

Rckol,



Thanks for the heads up.



But yes, now that I've gotten unstuck on my idea, light is streaming down from the heavens, angelic trumpets are sounding along with a chorus of Hosanna's and fuse blocks have acquired a golden glow.



All I had to do is let go of the idea of being able to see all my fuses. 



Probably will do some sort of blown fuse indicator LED instead, but that's a project for after I'm airborne.



John



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mrspudandcompany(at)veriz
Guest

Posted: Fri Jun 04, 2010 8:23 am Post subject: Long and short hot feeders

But yes, now that I've gotten unstuck on my idea, light is streaming down

from the heavens, angelic trumpets are sounding along with a chorus of

Hosanna's and fuse blocks have acquired a golden glow.



All I had to do is let go of the idea of being able to see all my fuses. 



Probably will do some sort of blown fuse indicator LED instead, but that's a

project for after I'm airborne.



John



		And that is the "Hot Feeders Long and Short of it"





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