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Breaker Wiring From Fuse Block

mfleming

mfleming

Well Known Member
Patron
Well, if that title doesn't confuse you, nothing will :D

My electrical system uses mostly fuses.
The way the fuse block is wired is, the fat wire from the battery contactor goes to the the big post on the fuse block.

BUT, I elected to use a couple of pullable breakers for the flaps & trim.

I'm thinking I just run the appropriate sized wire from the big post on the main bus fuse block to the breakers.

The question is: Do I protect this relatively short wire? AND if so, how?
 
In your situation, the "little" wire is just replacing what would have been the "big" wire running to a circuit breaker bus bar (the typical setup). The main supply wire isn't normally protected in that scenario so I see no problems with what you suggested.
 
Fat wire

Some builders protect the "fat wire" with an ANL fuse between contactor and fat wire.
 
wirejock said:
Some builders protect the "fat wire" with an ANL fuse between contactor and fat wire.
Click to expand...

True. There's also an argument for using a Class T rather than an ANL for the guys running LiPOs. However, I would guess that running the "fat" wires unprotected is still the most common method in both the certified and experimental world.
 
Just me

I chose to have a 35 amp anl at the firewall. And all wires after the anl that go to the breakers / fuses have a fusing current at 35 amps x 1.5. From the breakers /fuse, that wire is small and only rated for the value of the fuse/ breaker. This scheme means that any shorts will blow the upstream fuse / breaker / anl and not smoke the wire. This is the best way, I think, to keep wires from generating smoke if they short. It is not usually a problem when the aircraft is new, but rather as the aircraft ages.
 
how about a fuse link like some Z schematics show for the alternator CB

mfleming said:
... I elected to use a couple of pullable breakers for the flaps & trim.

I'm thinking I just run the appropriate sized wire from the big post on the main bus fuse block to the breakers.

The question is: Do I protect this relatively short wire? AND if so, how?
Click to expand...

Hi Michael,

I know you are using Z101 as a template. Why not protect the wire from from the main bus to the panel-mounted CBs with a fuse link the same way Z101 does with the alternator field breaker? Z101 shows store-bought 20 awg fuse link wire for the alternator field and you could use that for the trim motor and flap motor CBs also.
 
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ANL Current Limiter is more robust than a Fuse

PilotjohnS said:
I chose to have a 35 amp anl at the firewall. And all wires after the anl that go to the breakers / fuses have a fusing current at 35 amps x 1.5...
Click to expand...

I don't know the history/technical background of these things called ANL Current Limiters, except they seem to have originated at Bussmann, but, importantly, they are more robust than the typical things called Fuses.

A "35A" ANL doesn't melt until 80+ A.

An ANL's multiple of melting current to rated current goes down as rating goes up but for the smaller ones, the 35 to 60 A ANL's we use, it's over 2.
.
 

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  • Bussmann ANL melt curve.jpg
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My preference as an Electrical Engineer is to protect the wire. Since this wire is coming from the fuse block to feed multiple breakers, why not protect the wire with a suitably sized fuse in the fuse block? That way if the wire shorts, or the bus on the breakers shorts, the fuse will blow and protect both the wire and aircraft. I hate it when a short starts melting the aluminum aircraft!

Cheers
 
DRMA said:
My preference as an Electrical Engineer is to protect the wire. Since this wire is coming from the fuse block to feed multiple breakers, why not protect the wire with a suitably sized fuse in the fuse block? That way if the wire shorts, or the bus on the breakers shorts, the fuse will blow and protect both the wire and aircraft. I hate it when a short starts melting the aluminum aircraft!

Cheers
Click to expand...

This is what I did for two or three items that needed it. I upsized the short wire allowing a larger fuse to be used, the smaller breaker then controls the smaller downstream wire. So if there was ever a fault it will trip the breaker not the fuse first. If it trips the larger fuse or the breaker and fuse at the same time I got bigger problems that don’t need reset in flight.

Just to emphasize, if a larger fuse is used than the breaker the wire must be sized properly!
 
DRMA said:
My preference as an Electrical Engineer is to protect the wire. Since this wire is coming from the fuse block to feed multiple breakers, why not protect the wire with a suitably sized fuse in the fuse block? That way if the wire shorts, or the bus on the breakers shorts, the fuse will blow and protect both the wire and aircraft. I hate it when a short starts melting the aluminum aircraft!

Cheers
Click to expand...

jcarne said:
This is what I did for two or three items that needed it. I upsized the short wire allowing a larger fuse to be used, the smaller breaker then controls the smaller downstream wire. So if there was ever a fault it will trip the breaker not the fuse first. If it trips the larger fuse or the breaker and fuse at the same time I got bigger problems that don’t need reset in flight.

Just to emphasize, if a larger fuse is used than the breaker the wire must be sized properly!
Click to expand...

This is what I was thinking of doing, although I only have 2 fuse slots left in the main fuse bus block.

I guess I would size a wire for the 2 breakers and then put in an appropriately sized fuse.

Wasn't sure if this was considered a thing....having a fuse and breaker in series.
 
mfleming said:
This is what I was thinking of doing, although I only have 2 fuse slots left in the main fuse bus block.

I guess I would size a wire for the 2 breakers and then put in an appropriately sized fuse.

Wasn't sure if this was considered a thing....having a fuse and breaker in series.
Click to expand...

I’m sure someone will be along at some point to argue it but it works just fine and is even in some Knuckolls drawings. I would do it again.
 
mfleming said:
... Wasn't sure if this was considered a thing....having a fuse and breaker in series.
Click to expand...

I collect Bob Nuckolls quotes... here's one:

"If you extend the bus with a wire up to the breaker, it should be protected. If you use a fuse in the fuse block, then because of the much faster response time of a fuse, a 15A fuse might open faster than a 5A breaker . . . so we use a fusible link with a time constant that is greater than a breaker to protect that wire segment.

Bob . . ."​
 
jcarne said:
I’m sure someone will be along at some point to argue it but it works just fine and is even in some Knuckolls drawings. I would do it again.
Click to expand...

I've only noticed a fuse in series with a circuit breaker on one Z schematic, Z01.
  • That was a preliminary schematic Bob Knuckolls put out for discussion in 2020 where he showed a 30A fuse for the feeder to the 5A alternator field CB.
  • During that time Bob said "... I'm still wrestling with the notion of driving the crowbar ov breaker bus extension through a ATC fuse on the fuseblock. I cannot guarantee that every future builder would use a breaker having I(squared)t characteristics small enough to avoid popping that fuse."

Later in 2020, Z01 became Z101 which is at rev B showing a 20 awg fuse link protecting the feeder to the 5A alternator field CB. Bob was trying to avoid having to fabricate the 22 awg fuse link of legacy Z schematics, Tefzel wire inside fiberglass tube. Turns out the smallest fuse link wire available in small quantities is 20 awg so Bob went with that. Summit Racing has Pico brand. FYI if there is a rubber flag molded onto a fuse link wire it is a non-functional label.
.
 
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The problem with having 2 fuses in series is that in the case of a short circuit, both fuses could blow, even though the first fuse is much bigger. Then every thing down steam of the big fuse no longer works. That is why many planes are wired without a fuse protecting the main feeder. Good workmanship reduces the chances of the main feeder shorting out. The pilot can always shut off the battery contactor.
 
johnbright said:
I collect Bob Nuckolls quotes... here's one:

"If you extend the bus with a wire up to the breaker, it should be protected. If you use a fuse in the fuse block, then because of the much faster response time of a fuse, a 15A fuse might open faster than a 5A breaker . . . so we use a fusible link with a time constant that is greater than a breaker to protect that wire segment.

Bob . . ."​
Click to expand...

Yes he does seem to prefer fusible links. This would be a good option too. A better one now that I think about it.

johnbright said:
I've only noticed a fuse in series with a circuit breaker on one Z schematic, Z01. That was a preliminary schematic Bob put out for discussion in 2020 where he showed a 30A fuse for the feeder to the 5A alternator field CB.

Later in 2020, Z01 became Z101 which is at rev B showing a 20 awg fuse link protecting the feeder to the 5A alternator field CB.
.
Click to expand...

There is that one and I was also referencing his use of multiple fuses in series in certain situations. The old Z-13 I believe had one. Point was that many people think that if circuit protection is in series the world is going to end. There are certainly times where it's not right but it's not a blanket.

Mich48041 said:
The problem with having 2 fuses in series is that in the case of a short circuit, both fuses could blow, even though the first fuse is much bigger. Then every thing down steam of the big fuse no longer works. That is why many planes are wired without a fuse protecting the main feeder. Good workmanship reduces the chances of the main feeder shorting out. The pilot can always shut off the battery contactor.
Click to expand...

Very true and he has a good video showing this. However in my mind it still wouldn't bother me in certain cases. If something is shorted/overloaded to that point it doesn't need reset in the air. Just my thinking. I'm assuming the OP wants pullables to shut them down if necessary? Would be better to have them separate.


Michael, looking back on your original post I see it is flaps and trim, the latter is something I would not like to live without. Definitely doable but wouldn't be the funnest thing. Personally I would either run that wire off of a fusible link as it isn't going to nuisance trip like a fuse might. Double personally, I would separate those two circuits as I regard trim control as being too important to be paired with something else. Got any lights you can gang together to free up space? I'm no electrical engineer so take this at face value. I'm just glad your cranking the project out! :)
 
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Fuse/Breaker coordination is typically part of the design of industrial and high power electrical systems, in order to avoid upstream devices tripping prior to downstream devices. I'm not sure if the required current/time curves are published for our low current fuses and breakers however.

One possible solution would be to use a slow-blow fuse in your fuse block ahead of the wire going to the circuit breakers. If you are using an automotive blade type fuse block, you might consider one of these fuses: https://www.mouser.com/Circuit-Prot...NUZNFzbMpmqOqvvpeE29mwmCY-itR3w8aAn1JEALw_wcB

Regards
 
DRMA said:
Fuse/Breaker coordination is typically part of the design of industrial and high power electrical systems, in order to avoid upstream devices tripping prior to downstream devices. I'm not sure if the required current/time curves are published for our low current fuses and breakers however.

One possible solution would be to use a slow-blow fuse in your fuse block ahead of the wire going to the circuit breakers. If you are using an automotive blade type fuse block, you might consider one of these fuses: https://www.mouser.com/Circuit-Prot...NUZNFzbMpmqOqvvpeE29mwmCY-itR3w8aAn1JEALw_wcB

Regards
Click to expand...

This looks like an easy substitution for a fusible link...might be the ticket
icon14.gif
 
mfleming said:
This looks like an easy substitution for a fusible link...might be the ticket
icon14.gif
Click to expand...

The link from post #16 is to maxi size blade fuses. Seems like standard size blade fuses are not available slow blow.

I'm not saying a slow blow fuse is a proper solution. What's wrong with a fuse link?
.
 
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johnbright said:
The link from post #16 is to maxi size blade fuses. Seems like standard size blade fuses are not available slow blow.

I'm not saying a slow blow fuse is a proper solution. What's wrong with a fuse link?
.
Click to expand...

Fuse links are a bit of a mystery to me. Maybe if I had a more thorough understanding on how to make them, I might consider them.
 
mfleming said:
Fuse links are a bit of a mystery to me. Maybe if I had a more thorough understanding on how to make them, I might consider them.
Click to expand...

Here is link on how to make them. You can buy the material from B&C if I remember correctly.

You will need a larger size though so perhaps John can explain the sizing better.

They are very easy to make!

http://www.aeroelectric.com/articles/fuselink/fuselink.html

They are just a smaller wire that will burn open inside of a protectant sleeve. They are essentially acting as a fuse in a way.

Edit: looking at B&C website this one may be perfect for you. Not sure of your amp requirement though.

https://bandc.com/product/fusible-link-kit-20-16-awg/
 
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mfleming said:
Fuse links are a bit of a mystery to me. Maybe if I had a more thorough understanding on how to make them, I might consider them.
Click to expand...

The short story:
  • Decide what size feeder a particular CB needs. If it's less than 16 awg, up it to 16 awg because fuselink wire is not available smaller than 20 awg.
  • Pick a store-bought fuse link wire 4 awg smaller than the feeder and buy it from Summit Racing. Go to Summit and search "pico fusible link".
  • Crimp a ring terminal on one end of a 6" length of the fuselink wire and use a crimp butt splice to attach the feeder to the other end.

Those are good links Jereme posted.
  • Bob Nuckolls developed the fiberglass tubing over Tefzel wire method of fusible link construction and B&C sells kits. The fiberglass tubing contains the fire if the fuse link is ever called upon.
  • One kit, FLK-1, is described as 24-20. I guess that means they give you 24 awg wire and you use it to protect a 20 awg feeder. 24 awg fuse link wire is shown on some Z schematics at the alternator shunt.
  • The other kit, FLK-2, is described as 20-16. I guess that means they give you 20 awg wire and you use it to protect a 16 awg feeder. It would be easier to buy purpose-made fuse link wire since it is availabe 20 awg.
  • Many Z schematics show a 22 awg fuse link for an 18 awg feeder to the 5A alternator field breaker. I imagine B&C would put together a kit with 22 awg wire.
  • Fuse links are always 4 awg smaller than the protected wire.
  • Fuse links are normally 6" long.
  • The fiberglass tubing appears to be McMaster PN 2573K41, white.

Bob was looking to replace the home-made fuse link with store-bought fuse link wire which has insulation that will contain the fire if the fuse link is ever called upon.
  • Reason is easier fabrication although the home-made fiberglass-tubing-covered ones are not difficult.
  • 20 awg is the smallest available in small quantities.
  • Summit Racing has Pico brand.
  • If there is a rubber flag molded onto a fuse link wire it is a non-functional label.
  • This change was made in 2020 as part of Z101.
 
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My opinion, if the wire is short and easily routed and protected, why would you add multiple failure point(s)?
 
Walt said:
My opinion, if the wire is short and easily routed and protected, why would you add multiple failure point(s)?
Click to expand...

Good point IMO. If the wire is short and the builder is confident a short to ground is practically impossible.
.
 
johnbright said:
The short story:
  • Decide what size feeder a particular CB needs. If it's less than 16 awg, up it to 16 awg because fuselink wire is not available smaller than 20 awg.
  • Pick a store-bought fuse link wire 4 awg smaller than the feeder and buy it from Summit Racing. Go to Summit and search "pico fusible link".
  • Crimp a ring terminal on one end of a 6" length of the fuselink wire and use a crimp butt splice to attach the feeder to the other end.

Those are good links Jereme posted.
  • Bob Nuckolls developed the fiberglass tubing over Tefzel wire method of fusible link construction and B&C sells kits. The fiberglass tubing contains the fire if the fuse link is ever called upon.
  • One kit, FLK-1, is described as 24-20. I guess that means they give you 24 awg wire and you use it to protect a 20 awg feeder. 24 awg fuse link wire is shown on some Z schematics at the alternator shunt.
  • The other kit, FLK-2, is described as 20-16. I guess that means they give you 20 awg wire and you use it to protect a 16 awg feeder. It would be easier to buy purpose-made fuse link wire since it is availabe 20 awg.
  • Many Z schematics show a 22 awg fuse link for an 18 awg alternator field breaker feeder. I imagine B&C would put together a kit with 22 awg wire.
  • Fuse links are always 4 awg smaller than the protected wire.
  • Fuse links are normally 6" long.
  • The fiberglass tubing appears to be McMaster PN 2573K41, white.

Bob was looking to replace the home-made fuse link with store-bought fuse link wire which has insulation that will contain the fire if the fuse link is ever called upon.
  • Reason is easier fabrication although the home-made fiberglass-tubing-covered ones are not difficult.
  • 20 awg is the smallest available in small quantities.
  • Summit Racing has Pico brand.
  • If there is a rubber flag molded onto a fuse link wire it is a non-functional label.
  • This change was made in 2020 as part of Z101.
Click to expand...

Wow, the mystery is gone :D

So if I used a 14awg feeder to the breaker, I would purchase a 18awg fusible link from summit...right?
(notwithstanding the DIY version)
 
Walt said:
My opinion, if the wire is short and easily routed and protected, why would you add multiple failure point(s)?
Click to expand...

So, one of the wires goes from the main bus to the field breaker, which is a run of about two and a half feet. But its in a wire bundle and not exposed too much but the other wires.

The other runs are about eight inches away from the bus to the breaker but with twists and turns, let's say one and a half feet total.

Does that sound like wires you would be OK with without the fusible link?
 
Why complicate the installation and end up causing the short circuit that you are trying to protect
against with a fuselink. Sometimes the cure is worse than the disease. Listen to Walt.
 
mfleming said:
Wow, the mystery is gone :D

So if I used a 14awg feeder to the breaker, I would purchase a 18awg fusible link from summit...right?
(notwithstanding the DIY version)
Click to expand...

Correct... 18 awg fuselink to protect 14 awg feeder.

Pico PN 5555PT is single piece 8" long. 8123PT is 8' long for only $1 more.
.
 
mfleming said:
So, one of the wires goes from the main bus to the field breaker, which is a run of about two and a half feet. But its in a wire bundle and not exposed too much but the other wires.

The other runs are about eight inches away from the bus to the breaker but with twists and turns, let's say one and a half feet total.

Does that sound like wires you would be OK with without the fusible link?
Click to expand...

Yes, proper installation is the key to success. I don't do fusible links or protect feed wires, that's what the master contactor is for.
 
Walt said:
Yes, proper installation is the key to success. I don't do fusible links or protect feed wires, that's what the master contactor is for.
Click to expand...

I agree with you Walt.
We don't need fuses protecting fuses. Also it was mentioned earlier that if there are two fuses in series and one blows they will will both blow, this is not possible especially if one has a higher rating than the other.
 
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