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Building fusible links for FAT wires

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jcohen@post.com

Joined: 10 Mar 2022
Posts: 17

Posted: Fri Feb 10, 2023 2:10 pm Post subject: Building fusible links for FAT wires

In order to reduce the number of studs with nuts that could loosen in my Z101, I decided to use Fusible links 12AWG and 14AWG for my Pri and Aux Alternator Fault wires, 8AWG and 10AWG respectively. The AeroElectric Connection Article "How to Build Fusible Links" states this is for 22AWG and 24 AWG Fuse links only. 



So my question is, what is different in constructing larger FAT wire fusible links? And where can I purchase short lengths of Silicone covered Fiberglass Sleeving? It seems that is not sold by Spruce or B&C....

_________________
Jeff

Eric Page

Joined: 15 Feb 2017
Posts: 260

Posted: Fri Feb 10, 2023 2:22 pm Post subject: Re: Building fusible links for FAT wires

Search eBay for "silicone fiberglass sleeve". It's similar to fire sleeve, but available in thin-wall versions and small diameters.

Ceengland

Joined: 11 Oct 2020
Posts: 394
Location: MS

Posted: Fri Feb 10, 2023 2:28 pm Post subject: Building fusible links for FAT wires

On 2/10/2023 4:10 PM, jcohen(at)post.com wrote:

 	  Quote: 	
		   



 In order to reduce the number of studs with nuts that could loosen in my Z101, I decided to use Fusible links 12AWG and 14AWG for my Pri and Aux Alternator Fault wires, 8AWG and 10AWG respectively. The AeroElectric Connection Article "How to Build Fusible Links" states this is for 22AWG and 24 AWG Fuse links only.



 So my question is, what is different in constructing larger FAT wire fusible links? And where can I purchase short lengths of Silicone covered Fiberglass Sleeving? It seems that is not sold by Spruce or B&C....



 --------

 Jeff

Primary difference is the energy (heat) released if they 'blow'. This 
	


makes containing the event a lot harder with big links. The ideal 

solution is to just use off-the-shelf fusible link wire to make the 

links. Amazon has vendors with a good selection.

https://smile.amazon.com/s?k=fusible+link+wire&crid=2RG3WCVSNEZWS&sprefix=fusible+link+wire%2Caps%2C219&ref=nb_sb_noss_1



You can solder and heatshrink, or just use quality crimp terminals to 

join the link to the regular wire.



Charlie



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_________________
Charlie

johnbright

Joined: 14 Dec 2011
Posts: 166
Location: Newport News, VA

Posted: Fri Feb 10, 2023 2:39 pm Post subject: Re: Building fusible links for FAT wires

FLW 6" long and 4 awg smaller than the B lead, PICO brand is common; available from 10 to 20 awg.



Is the main alternator 60A... if so I would go with 6 awg B lead.

_________________
John Bright, RV-6A, at FWF, O-360
Z-101 single batt dual alt SDS EM-5-F.
john_s_bright@yahoo.com, Newport News, Va
N1921R links

jcohen@post.com

Joined: 10 Mar 2022
Posts: 17

Posted: Fri Feb 17, 2023 11:48 am Post subject: Re: Building fusible links for FAT wires

Now that I am having fun building fusible links for my Pri and Aux Alternator wires, I am using off the shelf Pico fusible link wire (12AWG and 14AWG) to build my FAT wire  links, should I still cover the wire with Fiberglass Sleeving? How does the off-the shelf FAT wire fusible link normally respond when it operates/ burns?  If the link can flame and is not covered by fiberglass sleeve, shouldn't the physical routing be considered, like not routing near/below the battery or other components?



My thought is, if one event causes the fusible link to operate ( burn), couldn't a flame from a FAT wire take out a nearby critical component (like the Master in Z101) and cause a second failure?

_________________
Jeff

Ceengland

Joined: 11 Oct 2020
Posts: 394
Location: MS

Posted: Fri Feb 17, 2023 1:41 pm Post subject: Building fusible links for FAT wires

On 2/17/2023 1:49 PM, jcohen(at)post.com wrote:

 	  Quote: 	
		   



 Now that I am having fun building fusible links for my Pri and Aux Alternator wires, I am using off the shelf Pico fusible link wire (12AWG and 14AWG) to build my FAT wire  links, should I still cover the wire with Fiberglass Sleeving? How does the off-the shelf FAT wire fusible link normally respond when it operates/ burns?  If the link can flame and is not covered by fiberglass sleeve, shouldn't the physical routing be considered, like not routing near/below the battery or other components?



 My thought is, if one event causes the fusible link to operate ( burn), couldn't a flame from a FAT wire take out a nearby critical component (like the Master in Z101) and cause a second failure?



 --------

 Jeff

Hi Jeff,
	




If you're buying purpose-built fuse-link wire, the insulation should be 

designed to contain the 'event'. Look at the difference in both material 

and thickness of the insulation. It's probably good practice to avoid 

bundling the short segment of fuselink wire into a larger bundle, but 

there usually wouldn't be any need to do that, anyway. If you have 

serious doubts/questions, then make yourself a test rig and test a 

segment (common sense protections for yourself and other stuff obviously 

applies).



The fiberglass sleeving trick is typically used for the small gauge 

links that are user-fabbed from regular small gauge wire that has 

typical aircraft insulation.



Charlie



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_________________
Charlie

jcohen@post.com

Joined: 10 Mar 2022
Posts: 17

Posted: Fri Feb 17, 2023 2:08 pm Post subject: Re: Building fusible links for FAT wires

 	  Ceengland wrote: 	
		  On 2/17/2023 1:49 PM, jcohen(at)post.com wrote:

 	  Quote: 	
		   



 Now that I am having fun building fusible links for my Pri and Aux Alternator wires, I am using off the shelf Pico fusible link wire (12AWG and 14AWG) to build my FAT wire  links, should I still cover the wire with Fiberglass Sleeving? How does the off-the shelf FAT wire fusible link normally respond when it operates/ burns?  If the link can flame and is not covered by fiberglass sleeve, shouldn't the physical routing be considered, like not routing near/below the battery or other components?



 My thought is, if one event causes the fusible link to operate ( burn), couldn't a flame from a FAT wire take out a nearby critical component (like the Master in Z101) and cause a second failure?



 --------

 Jeff

Hi Jeff,

	




If you're buying purpose-built fuse-link wire, the insulation should be 

designed to contain the 'event'. Look at the difference in both material 

and thickness of the insulation. It's probably good practice to avoid 

bundling the short segment of fuselink wire into a larger bundle, but 

there usually wouldn't be any need to do that, anyway. If you have 

serious doubts/questions, then make yourself a test rig and test a 

segment (common sense protections for yourself and other stuff obviously 

applies).



The fiberglass sleeving trick is typically used for the small gauge 

links that are user-fabbed from regular small gauge wire that has 

typical aircraft insulation.



Charlie



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This email has been checked for viruses by Avast antivirus software.

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Thank you Charlie. I will bench test  the link to understand more of how the link reacts.  Would there be any downside to attaching the 6” link at the B terminal of the pri alternator , rather than at the terminal on the starter contactor as depicted on Z101? That could help with fire proximity issues with contactors and/or battery. That implementation still protects the entire wire the same way, even when the protection is on the other “end” , right?

_________________
Jeff

Ceengland

Joined: 11 Oct 2020
Posts: 394
Location: MS

Posted: Fri Feb 17, 2023 2:30 pm Post subject: Building fusible links for FAT wires

On 2/17/2023 4:08 PM, jcohen(at)post.com wrote:

 	  Quote: 	
		   

 Ceengland wrote:

> On 2/17/2023 1:49 PM, jcohen(at)post.com wrote:

>

>>   

>>

>>   Now that I am having fun building fusible links for my Pri and Aux Alternator wires, I am using off the shelf Pico fusible link wire (12AWG and 14AWG) to build my FAT wire  links, should I still cover the wire with Fiberglass Sleeving? How does the off-the shelf FAT wire fusible link normally respond when it operates/ burns?  If the link can flame and is not covered by fiberglass sleeve, shouldn't the physical routing be considered, like not routing near/below the battery or other components?

>>

>>   My thought is, if one event causes the fusible link to operate ( burn), couldn't a flame from a FAT wire take out a nearby critical component (like the Master in Z101) and cause a second failure?

>>

>>   --------

>>   Jeff

>> Hi Jeff,

>>

>

> If you're buying purpose-built fuse-link wire, the insulation should be

> designed to contain the 'event'. Look at the difference in both material

> and thickness of the insulation. It's probably good practice to avoid

> bundling the short segment of fuselink wire into a larger bundle, but

> there usually wouldn't be any need to do that, anyway. If you have

> serious doubts/questions, then make yourself a test rig and test a

> segment (common sense protections for yourself and other stuff obviously

> applies).

>

> The fiberglass sleeving trick is typically used for the small gauge

> links that are user-fabbed from regular small gauge wire that has

> typical aircraft insulation.

>

> Charlie

>

> -- 

> This email has been checked for viruses by Avast antivirus software.

> www.avast.com



 Thank you Charlie. I will bench test  the link to understand more of how the link reacts.  Would there be any downside to attaching the 6â€ link at the B terminal of the pri alternator , rather than at the terminal on the starter contactor as depicted on Z101? That could help with fire proximity issues with contactors and/or battery. That implementation still protects the entire wire the same way, even when the protection is on the other â€œendâ€ , right?



 --------

There is a downside to placing it at the alternator. Remember, the fuse 
	


(whether CB, link, or actual fuse) is there to protect the wire. The 

alternator B lead wire should be big enough to handle the highest 

current the alternator can create (usually a small percentage higher 

than its 'rated' output), so there's no need to protect the wire from 

the alternator. The danger to the B lead is from the *battery*. So the 

fusing device should be on the 'dangerous' end, to protect the wire. (It 

is confusing, when you have devices at both ends that are both capable 

of producing current.)



Charlie

_________________
Charlie

johnbright

Joined: 14 Dec 2011
Posts: 166
Location: Newport News, VA

Posted: Fri Feb 17, 2023 3:54 pm Post subject: Re: Building fusible links for FAT wires

 	  jcohen(at)post.com wrote: 	
		  ... I will bench test  the link to understand more of how the link reacts.  Would there be any downside to attaching the 6” link at the B terminal of the pri alternator , rather than at the terminal on the starter contactor as depicted on Z101? That could help with fire proximity issues with contactors and/or battery. That implementation still protects the entire wire the same way, even when the protection is on the other “end” , right? 	




The way I express it is the protection (relay, contactor, fuse, current limiter, CB, fusible link) should be as close as possible to the power source which in this case is the battery. The battery can put out hundreds of amps and the alternator can only put out its rating (plus a little more if it's cold) so it is not capable of damaging itself or the B lead.



Suppose the alternator B leads gets pinched to ground somehow... one wants the fuselink to open before the battery self-destructs.



I don't imagine a melted B lead fuselink will create enough fire to burn the contactor case. Bob Nuckolls shows the fuselink at the contactor for a reason. I look forward to your experiment of burning one. A 12 awg wire will burn at ~235A and a 14 awg at ~166A.



BTW, what is the rating of your alternator?

_________________
John Bright, RV-6A, at FWF, O-360
Z-101 single batt dual alt SDS EM-5-F.
john_s_bright@yahoo.com, Newport News, Va
N1921R links

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Feb 17, 2023 4:52 pm Post subject: Building fusible links for FAT wires

 	  Quote: 	
		  Suppose the alternator B leads gets pinched to ground somehow... one wants the fuselink to open before the battery self-destructs. 	


    Wire damage is unlikely. Shorted diodes in alternator

    is more likely but still rare.



  	  Quote: 	
		  I don't imagine a melted B lead fuselink will create enough fire to burn the contactor case. 	


    The definition of any fusible circuit protection is

    "a means by which a conductor can be protected

     from catastrophic failure due to hard fault

     down stream of a potentially hazardous energy

     source."



    In our cases, potentially hazardous energy sources

    start with a battery (1000 amps) joined in relatively

    minor concert with alternator(s) (40 to 125A?).



    Circuit protection should function to clear the

    faulted feeder with MINIMAL damage to adjacent

    hardware and zero propagation to other systems.

    Oh yeah, any by-products of fault clearance activity

    should not become a hazard to occupants of the

    machine (smoke).  This applies to all vehicles

    including but not limited to rail locomotives,

    trucks and yeah, airplanes.



  	  Quote: 	
		   Bob Nuckolls shows the fuselink at the contactor for a reason. I look forward to your experiment of burning one. A 12 awg wire will burn at ~235A and a 14 awg at ~166A. 	


    The wire to be protected in this instance

    is the alternator b-lead itself. The energy

    source is the battery. The fault will most

    likely be failed rectifier in the alternator.



    I've 'smoked' a number of COTS (commercial off

    the shelf) fusible link wires. Those current

    'ratings' are irrelevant in the face of probable

    fault conditions probably exceeding 1000 amps.



    The smoke generated was not 'pleasant' but not

    debilitating and short lived. Damage to said insulation

    was remarkably minor. Fusible link insulation

    is intended to contain the effects of a fused

    wire such that damage to materials and components

    outside that insulation is minimized. See "Hypalon"

    insulation history.



  	  Quote: 	
		  BTW, what is the rating of your alternator? 	


    Relevant only to the extent of sizing b-lead

    wire conductor size to limit voltage drop

    to design goals . . . generally on the order

    of a few hundred millivolts at full load.



    I've got some videos of fusible link burns

    that I'll try to dig up . . . or perhaps

    duplicate.



    



 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Feb 17, 2023 4:55 pm Post subject: Building fusible links for FAT wires

 	  Quote: 	
		  There is a downside to placing it at the alternator. Remember, the fuse (whether CB, link, or actual fuse) is there to protect the wire. The alternator B lead wire should be big enough to handle the highest current the alternator can create (usually a small percentage higher than its 'rated' output), so there's no need to protect the wire from the alternator. The danger to the B lead is from the *battery*. So the fusing device should be on the 'dangerous' end, to protect the wire. (It is confusing, when you have devices at both ends that are both capable of producing current.) 	


    B-lead protection is ALWAYS designed to deal

    with BATTERY faults as the potentially hazardous

    condition. An alternator is physically incapable

    of opening its own b-lead protection.



    BATTERIES are always the driving consideration for

    placement and sizing of fusible links and/or current

    limiters (ANL, ANN, MANL, etc).



 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

johnbright

Joined: 14 Dec 2011
Posts: 166
Location: Newport News, VA

Posted: Fri Feb 17, 2023 6:26 pm Post subject: Re: Building fusible links for FAT wires

 	  nuckolls.bob(at)aeroelect wrote: 	
		  



  	  Quote: 	
		  BTW, what is the rating of your alternator? 	


    Relevant only to the extent of sizing b-lead

    wire conductor size to limit voltage drop

    to design goals . . . generally on the order

    of a few hundred millivolts at full load.



   Bob . . . 	




I’m just curious the OP chose 8 awg main alternator B lead. I have the impression main alternators are usually 60A with 6 awg B lead. This is an RV-7 with SDS EFI+I so current demands are higher than without EFI+I. I understand conductor sizing is not an exact science and the smaller wire will just get a little warmer and drop a little more voltage without being a safety issue.



My notes show 8 awg rated 40A and 6 awg 54A for the 10C rise criteria. I understand this is conservative when not in a bundle.



My load analysis for four cylinder SDS EFI+I ship shows 44A with both pumps running in addition to pitot heat, seat heat, lambda sensor, landing nav and strobe lights, dual Skyview and its accessories… so in reality 8 awg is not a problem.

_________________
John Bright, RV-6A, at FWF, O-360
Z-101 single batt dual alt SDS EM-5-F.
john_s_bright@yahoo.com, Newport News, Va
N1921R links

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Feb 18, 2023 10:23 am Post subject: Building fusible links for FAT wires

 	  Quote: 	
		  My load analysis for four cylinder SDS EFI+I ship shows 44A with both

 pumps running in addition to pitot heat, seat heat, lambda sensor,

 landing nav and strobe lights, dual Skyview and its accessories…

 so in reality 8 awg is not a problem. 	


   8AWG wire has 0.63 milliOhms/ft. At 60A full alternator

   load, this would drop 60 x 0.00063 = 0.038 or 38 milliVolts

   per foot of b-lead. A trivial significance even if you

   were able to achieve this unlikely operating load.



   You are correct, this single conductor hanging out in the air

   would not be at risk for compromise in your proposed

   configuration.



   My drawings tend to show 4AWG throughout the FAT wire

   matrix because it works in the full constellation of

   situations. It minimizes the need to scrounge up

   little chunks of assorted wire sizes, terminals and

   crimp tools just to satisfy some design goal for

   'optimizing' wire sizes . . . especially since 'optimal'

   has no industry wide definition. The weight penalties

   for a slightly oversized wire are very small

   while the fabrication and procurement benefits for

   'one size fits all' are significant.



   My '87 pick-em-up truck has an 10AWG b-lead feeder.

   Alternators for that truck could be as beefy as 90A!



   Hmmmm . . . 90A x 0.001 ohms/ft x 2 feet is 0.180

   volts . . . ho hum. The wire is hanging out in a big

   breeze.



   Speaking of crimp tools . . .



   A few years ago I snapped up a Harbor Freight

   offering for a hand-held, hydraulic crimping

   tool that came with a set of hex dies. The

   dies proved to be next to useless . . . too

   large of step between the graduation of sizes.

   Took the thing back to HF.



   A new kid on the block has appeared on Amazon,

   et. als. with a more granular selection of hex

   dimensions. I'm doing some test crimps on various

   combinations of materials and developing a

   process by which the OBAM aircraft builder's

   probability of reliable crimps is very high.



   Here's one of many examples:



  https://tinyurl.com/2e8evels



   There are offerings with more than 9 die

   sets but these tend to add big honk'n

   dies for wire that your airplane could

   could not lift!



   Watch this space . . .



 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

Ceengland

Joined: 11 Oct 2020
Posts: 394
Location: MS

Posted: Sat Feb 18, 2023 10:47 am Post subject: Building fusible links for FAT wires

 	  Quote: 	
		             A new kid on the block has appeared on Amazon,

           et. als. with a more granular selection of hex

           dimensions. I'm doing some test crimps on various

           combinations of materials and developing a

           process by which the OBAM aircraft builder's

           probability of reliable crimps is very high.

         

           Here's one of many examples:

         

                    https://tinyurl.com/2e8evels

         

           There are offerings with more than 9 die

           sets but these tend to add big honk'n

           dies for wire that your airplane could

           could not lift!

         

           Watch this space . . .

         

                

             Bob . . .

            	
     I've got a similar unit; biggest issue for me was that the dies are     labeled in metric sizes, with no cross reference. So when I was     using it I had to 'guestimate' which die set to use. Looks like the     current selection has a cross reference.

     

     Charlie

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Charlie

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