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Would you install a ANL 50amp fuse

ron sterba

Well Known Member
Was considering installing a fuse holder on my 9A firewall with a 50 amp fuse that would feed my main buss in the cockpit. This fuse holder would be installed near my Master relay, on the engine side of the firewall. Has anybody done this? What kind of fuseholder/ block would you use. I saw one on a firewall once that was about 3" long in black color & with a plastic clear cover. It had a 50 amp fuse. I believe they call them ANL fuse? Quarter inch hole on one end and a "U" shape on the other. My condition inspection is due shorty. Any ideas always appreciated. Thanks

Ron in Oregon RV9A N421HJ just one away from the Honda Jet and a whole lot more fun to fly! Course unless you are in a hurry.
 
I have three 80 amp ANLs, one from the B+ PP 70 amp alt, another one to feed the plane after contactor, and one at the backup 20 AH battery.
 
resettable/replaceable in flt?

It sounds like this would be a serious failure if it occurred in flt. I think I would want it accessible if it blew in flt.
 
It is common practice to put these on the firewall so you don't have a hot, unprotected B-lead running directly into the cockpit, as was practiced for many years.

If you have a 60 amp alternator, use an 80 amp limiter. I have never had one blow. They are very slow to blow, not like a CB or normal fuse, and are there to mainly protect against a dead short.

I highly recommend using one. Have been doing it for many years, as have others.

Vic
 
Plus one on everything Vic says.

It is common practice to put these on the firewall so you don't have a hot, unprotected B-lead running directly into the cockpit, as was practiced for many years.

If you have a 60 amp alternator, use an 80 amp limiter. I have never had one blow. They are very slow to blow, not like a CB or normal fuse, and are there to mainly protect against a dead short.

I highly recommend using one. Have been doing it for many years, as have others.

Vic
 
I have a plane &power 60amp alternator I used a 60amp ANL, is that the wrong amperage?
 
I have a plane &power 60amp alternator I used a 60amp ANL, is that the wrong amperage?

Should be ok - have a look at the specific data sheets for that fuse, it will show the time to open vs current.

I used this brand - it shows as a minimum opening time at full rated of about 4 hours..., max opening time at rated of infinity. They are designed to be matched to the alternators. 120s opening time minimum, 30 minutes maximum, at 135% of rated.

http://www.littelfuse.com/~/media/automotive/datasheets/fuses/passenger-car-and-commercial-vehicle/bolt-down-fuses/littelfuse_mega_datasheet.pdf

That brand is about $7 plus a couple dollars shipping from Digikey.
 
I do not think that Bob Nuckolls recommends a fuse ( or ANL limiter) on the power supply from the master to the main bus. He states his reasons for this in the AeroElectric Connection Manual. He does however recommend one be used at the firewall end of the alternator B lead. This "fuse" must obviously be rated beyond the maximum current output of the alternator. This "fuse" is to protect the alternator (and the B-lead running from the alternator) in the event that there is a short to ground in the diodes at the alternator resulting in a full battery current surge to the alternator.

Having said that I do believe there are obvious very real pitfalls in discussing these type of electrical architecture decisions on VansAirforce without reference to an actual drawing. Too easy for novices to get confused.
 
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I do not think that Bob Nuckolls recommends a fuse ( or ANL limiter) on the power supply from the master to the main bus.

I can think of both pros and cons, but tell us why Bob doesn't like it.

He does however recommend one be used at the firewall end of the alternator B lead. This "fuse" must obviously be rated beyond the maximum current output of the alternator. This "fuse" is to protect the alternator (and the B-lead running from the alternator) in the event that there is a short to ground in the diodes at the alternator resulting in a full battery current surge to the alternator.

It just protects the airplane. The B-lead is running through the engine compartment, an area full of hot and vibrating things. Short the B-lead through worn or melted insulation, or break it away from the B-terminal, and it can short to almost anything in the compartment with full battery amps.
 
Should be ok - have a look at the specific data sheets for that fuse, it will show the time to open vs current.

I used this brand - it shows as a minimum opening time at full rated of about 4 hours..., max opening time at rated of infinity. They are designed to be matched to the alternators. 120s opening time minimum, 30 minutes maximum, at 135% of rated.

http://www.littelfuse.com/~/media/automotive/datasheets/fuses/passenger-car-and-commercial-vehicle/bolt-down-fuses/littelfuse_mega_datasheet.pdf

That brand is about $7 plus a couple dollars shipping from Digikey.

This is interesting since I was getting ready to start a thread "Is the ANL Fuse Obsolete?"

This is talking about the type of fuse/limiter, not having a fuse.

A decade ago the ANL fuses were everywhere and I remember I got mine from Home Depot. All common sizes in cards hanging on an aisle wall.

Update - apparently Buss has stopped making them and the are now considered obsolete, having been replaced by smaller devices such as the ones linked to above.

I blew one during final assembly of my -6A (my fault, not any equipment) and the only one I could get locally was expensive and 100 Amps only. Ebay still has them but even my local friendly ACE store couldn't special order them.

The usual auto use for these type of devices is for the drivers with high power (ie very loud :) ) audio systems. I think we need to find out what is popular with them them and get a new standard for our firewalls.

Meantime, if you have an existing ANL fuse buy a few spares now on Ebay.
 
What you described works fine. B&C specialty has pictures of them on their website.

http://www.bandc.aero/anlcurrentlimiterbase-1.aspx


Vic
Hello VIC, whoa that's a great response guys. Gee been flying for a year without a fuse in-o to the main buss from the Master relay. Vic I did order that holder and 60 amp ANL fuse , thanks BIC! They didn't have a 50 amp so I went with a 60 amp. I want to thank all you builders for your input, been very helpful.
 
Alternator B-lead fuse

I also used the littlefuse - very nice product.

img_9452-1024x768.jpg


More pictures of my installation here:

http://www.rv8.ch/alternator-b-lead-install-with-littelfuse-midi-inline-80amp-fuse/
 
Not to pick on Alex's photo, but if you use a device like this, be sure it's mounted where vibration and/or stress won't kill it. Most of them are intended to be mounted in a stable holder of some sort; the fuse link isn't structural for itself. (The one in Alex's pic might well be intended for unsupported use; I don't know.)

Another option, especially for alternator B-leads and medium-current feeds into the cockpit, is a fabricated fusible link. Any wire can be protected by a short length of wire 4 gauge numbers smaller, ~4-6 inches long. EX: an 8 gauge wire can be protected with a 12 gauge fusible link. The upside is that the link can be soldered in. There are fewer joints to potentially fail, and it will never 'blow' unless there's a truly catastrophic fault (the only reason this sort of protection is included).

Nuckolls used to recommend them, until the high current, small, bolt-in links became common. Car makers have used them for decades in the engine compartment.

With electrically dependent engines getting more common, they are worth a look.

You can buy made-for-the-job fuselink wire in the larger sizes, or you can roll your own using tefzel wire and either woven fiberglass sheathing as a flash container, or for small gauge stuff, I've been using silicone tubing. (Destructive tested 22 gauge as a fusible link for 18 gauge.)
 
Not to pick on Alex's photo, but if you use a device like this, be sure it's mounted where vibration and/or stress won't kill it. Most of them are intended to be mounted in a stable holder of some sort; the fuse link isn't structural for itself. (The one in Alex's pic might well be intended for unsupported use; I don't know.)

Another option, especially for alternator B-leads and medium-current feeds into the cockpit, is a fabricated fusible link. Any wire can be protected by a short length of wire 4 gauge numbers smaller, ~4-6 inches long. EX: an 8 gauge wire can be protected with a 12 gauge fusible link. The upside is that the link can be soldered in. There are fewer joints to potentially fail, and it will never 'blow' unless there's a truly catastrophic fault (the only reason this sort of protection is included).

Nuckolls used to recommend them, until the high current, small, bolt-in links became common. Car makers have used them for decades in the engine compartment.

With electrically dependent engines getting more common, they are worth a look.

You can buy made-for-the-job fuselink wire in the larger sizes, or you can roll your own using tefzel wire and either woven fiberglass sheathing as a flash container, or for small gauge stuff, I've been using silicone tubing. (Destructive tested 22 gauge as a fusible link for 18 gauge.)

Good point regarding support. Mine is very well supported top and bottom (the top is mounted to a copper bar, which is in turn mounted to a block with the current sensing shunt). I would not mount one without support on both ends.
 
Being a auto, med, heavy truck tech, it can be frustrating trying to find and identify a burnt fusible link in a harness, some will burn the insulation, and some won't, one or two in a plane you built and know where they are is a different story. They were installed in vehicles a long time ago to deal with current start up induced load, (the start up current would blow a fuse rated for the running current) old heavy HVAC fan motors ECT. :rolleyes:
 
Bob Nuckols on protecting "fat" wires

I can think of both pros and cons, but tell us why Bob doesn't like it.

In working on my electrical system design I reference Aeroelectric Connection and Aeroelectric List. I assembled some notes on Bob Nuckols' opinion regarding circuit protection of "fat" wires, from Aeroelectric List, below.

Note there is protection in the cockpit in terms of being able to shut off the master relay and being able to remove alternator field current. And of course every connection is a potential failure.

=======================

Bob quotes the FARs:

Sec. 23.1357 Circuit protective devices.

(a) Protective devices, such as fuses or circuit breakers, must be installed in all electrical circuits other than--
(1) Main circuits of starter motors used during starting only; and
(2) Circuits in which no hazard is presented by their omission.

(b) A protective device for a circuit essential to flight safety may not be used to protect any other circuit.

(c) Each resettable circuit protective device ("trip free" device in which the tripping mechanism cannot be overridden by the operating control) must be designed so that--
(1) A manual operation is required to restore service after tripping; and
(2) If an overload or circuit fault exists, the device will open the circuit regardless of the position of the operating control.

(d) If the ability to reset a circuit breaker or replace a fuse is essential to safety in flight, that circuit breaker or fuse must be so located and identified that it can be readily reset or replaced in flight.

(e) For fuses identified as replaceable in flight--
(1) There must be one spare of each rating or 50 percent spare fuses of each rating, whichever is greater; and
(2) The spare fuse(s) must be readily accessible to any required pilot.

=========================

Some quotes from Bob:

“I'll direct your attention to paragraph (a)(2) which speaks to battery feeders and feeders to main power distribution busses that are typically the largest wires in the airplane and are not subject to being "smoked" by downstream faults. You can comfortably leave out the fuse you've cited.

A 12AWG wire is probably too small to be a bus feeder. When wiring with truly "fat" wires (6AWG or larger) they're not at high risk for burning due to shorts or overloads. Take a look at the wiring diagrams for any single engine TC aircraft and you'll find that few if any will incorporate fuses or current limiters in these pathways. This philosophy is echoed in the FARS…

Faulted robust wires generally arc to ground and burn their faults clear. Further, they're easily installed with attention to mechanical details such that faults to ground are as probable as losing one's propeller due to bolt failure.

The Z-figures are crafted with this philosophy in mind supported by a confidence in nearly 100 years of field history. I'll suggest that none of your fat wires should be smaller than 6AWG and that protection beyond what is illustrated in the Z-figures is no-value-added weight, cost and complexity.”

=====================
 
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All good points and we can wire these flying machines how we like, but one point that Dan brought up and one I agree with is the ANL to the alternator, If....the B+ lead came off in flight at the alternator, you would no know you had a flopping around stick arch wire burning everything it touches, and if it made a good contact, where would the reverse current load go? would it burn out the stud and disc in the master relay? or worse, This is not a short piece of copper bar bolted down hard, this wire goes a long way from the firewall through the engine mount to a vibrating fan twister, some of these alternator wires are 8-6 ga and will carry a lot of current to cause damage if not protected. I have one, to each their own. :D
 
Just to be clear, Nuckolls' writings/drawings include a protection device at the battery end of the alternator B-lead.

The 'fat wires' mentioned are the very heavy gauge lines from the battery to the main contactor, and to the starter.
 
Fat wires

Just to be clear, Nuckolls' writings/drawings include a protection device at the battery end of the alternator B-lead.

The 'fat wires' (post 18) mentioned are the very heavy gauge lines from the battery to the main contactor, and to the starter.

My understanding is:

The lead from the battery contactor to the main bus is a long "fat" wire.

The starter contactor is there to disconnect in case of a problem downstream from it.

One of Bob Nuckols' stories:

"Bottom line is that you're many, many times more likely to have a bad day in the cockpit for reasons far removed from a hard ground fault on your 6AWG bus feeder wire. . . and THAT because you didn't conduct due diligence in its installation.

In the case of the bus feeder, the risks are not so much to the wire as to the thing the wire touches.

Case in point: C90 twin turboprop on short final experiences disconnect of elevator cables. Pilot uses trim commands and power to execute go-around, assesses the condition and successfully lands the airplane with rudder, trim and power.

Pulling up floorboards in the cockpit revealed a 40A protected feeder to the windshield de-ice inverter had been mis-positioned against the elevator control cable during a maintenance operation. Over what had to be many hours of operation, motion of the cable wore through the insulation bringing the cable into contact with the hot wire. The arcing and sparking was of insufficient intensity to come to attention of crew in spite of the fact that it was going on virtually under their feet.

The copper wire was barely damaged. The breaker never popped while the elevator cable eventually eroded through and parted. Compare thermal properties of copper versus steel . . . this explains why the best steel safes have intermediate layers of copper in their construction. It's EASY to burn through steel . . . next to impossible on copper.

This narrative explains the high order probability that even if you DID get your 6AWG feeder faulted to ground, it's most likely to be a soft fault that burns a hole in your airplane while doing little damage to the wire . . . and certainly far short of getting it to smoke and/or open a fuse/breaker.

Adding 'protection' to this pathway doubles the number of joints in the pathway and adds nothing demonstrable in terms of fault response . . . which is why the spam-can builders don't do it either.

... Bob Nuckolls ..."
 

Yes, they are still around, but I could only find 100A and 200A ones for around $25 or more each in all of Tucson.

This compares to the past when they were simply items on the rack at Home Depot, Lowes and ACE hardware.

If you are building new I would go to a smaller, and currently more popular, size fuse such as the midi one listed earlier.

If you have ANL fues installed in your RV, then go to your local West Marine store (yes, they have them in AZ, but no 50A stock in all of Phoenix) or order on-line and have one or two in hand in your hangar. :)
 
Yes, they are still around, but I could only find 100A and 200A ones for around $25 or more each in all of Tucson.

This compares to the past when they were simply items on the rack at Home Depot, Lowes and ACE hardware.

If you are building new I would go to a smaller, and currently more popular, size fuse such as the midi one listed earlier.

If you have ANL fues installed in your RV, then go to your local West Marine store (yes, they have them in AZ, but no 50A stock in all of Phoenix) or order on-line and have one or two in hand in your hangar. :)

Did you try B&C Specialties?

http://www.bandc.aero/anlcurrentlimiters40athrough130a.aspx
 
Skylor I did purchase both the holder and fuse at B & C. THEY ARE ON THERE WAY BY WAY OF THE FASTEST DELIVERY UNITED STATES POSTAL SERVICE.
RON IN oregon RV9A
 
Fat Wires

John,

I confess; I didn't copy & paste the entire book. :)

As (I thought) someone had already pointed out, bus feeders are protected by their contactors, and fusing them adds failure points.
 
This narrative explains the high order probability that even if you DID get your 6AWG feeder faulted to ground, it's most likely to be a soft fault that burns a hole in your airplane while doing little damage to the wire . . . and certainly far short of getting it to smoke and/or open a fuse/breaker.
... Bob Nuckolls ..."

Shorting a 6AWG to ground is "...far short of getting it to smoke and/or open a fuse breaker."

Interesting. I like the logic, but this may call for an experiment ;)
 
I like the ANL for what I am using it for, and the clamp force of the nut and stud on the fuse ends. For example, I have seen a lot of problems with power feeds on International trucks that use a standard size ATO 40 amp fuse to power the ECM, what I have seen is the clamp force and contact size of the holder on the fuse blades is inadequate for the amount of current, over time this contact area gets compromised and causes all kinds of problems, first its intermittent, (hard to find), and then an open circuit at the contact points. I like the overkill of the ANL for what it is powering.....for me, no electrons.....no fan. :rolleyes:
 
Previously I said:

Shorting a 6AWG to ground is "...far short of getting it to smoke and/or open a fuse breaker."

Interesting. I like the logic, but this may call for an experiment ;)

I have huge respect for Bob's work, and like many of you, consider his AEC manual an essential bookshelf reference. However, in retrospect I do find some fault in his logic regarding circuit protection on a main bus feed.

The cautionary tale involved a 40A feeder which came into shorted contact with an elevator cable. Eventually the cable parted, without blowing the fuse, the supposed lesson being whatever component a robust cable shorts against is likely to burn up (burn an open) before the fuse can blow. That is undoubtedly true when the victim is not robust. However, does it hold true if the victim is a motor mount, or the stainless firewall, or some other component with significant mass?

Now consider time vs fuse opening ("before it can blow"). Alex posted a link to some sample fuse specifications, where it states the expected open time is 1 second at 200% of rated load. We're talking about a battery-fed short, which can dump very large currents, so 200% or more can be expected. There is more than enough amps available to pop the fuse.

Assume we do insert circuit protection at the main bus feeder source, properly sized for the wire...say 60A max for a #6 wire. Now let's short that wire somewhere in the cockpit. if the short burns an immediate open in less than one second, great. We'll get a flash and a few sparks and maybe some dirty drawers, but smoke should be limited and it probably won't release enough energy to serve as an ignition source for fibers and plastics. This is what Bob speaks of when he describes why the certified airplanes don't have circuit protection on bus feeds.

Should the short not burn open, given a typical Nuckolls wire plan the pilot is expected (1) overcome his surprise, (2) close the essential bus switch, and (3) open the master switch. No argument; it should work. However, how fast does it work? Is it likely to be less than one second? That's all the time the above passive circuit protection would have required, with no pilot action at all.

(BTW, remember Bob's cautionary tale leading to his introduction of the essential bus concept? The big cockpit short didn't burn open.)

Good design is the art of compromise. The key compromise to be weighed here is the addition of another set of connections (and a few ounces), vs the probability of any practical value. I would caution that blanket judgments may not be appropriate. Allow an example.

Assume a VFR RV-8 with a rear battery. We all seem to agree about the value of circuit protection on the alternator B-lead. There isn't any reason why the main bus feed can't share the same fuse...no additional connections or components.

 
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Dan, you're protecting the wrong end of the wire.

edit: I should explain the logic. The alt B lead should be sized to easily handle the max current the alt can deliver. Therefore, it can't overheat & damage insulation from alternator power. The alternator is 'self limiting', and will only do what it can to supply demand, and won't be damaged by the load. So there's no need to protect the wire from the alternator, or protect the alternator itself.

However, the battery *can* cook that wire.

2nd edit: What does the start circuit look like, with that design? Do you mount the starter contactor in the tailcone, with the battery & master? If so, you now have 2 very long #2 wires the length of the plane, instead of one (with starter contactor on the firewall). If the start contactor is on the firewall, how do you fuse the run from master to firewall (it now carries start current)?
 
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Alt

I had a problem on start up last year my GPS handheld that's mounted in panel SMOKED my batt is in back turned off my master and everything was still on on main buse still powered up with master off.Turned engine off everything on panel shut off,sit there puzzled as to what just happened always thought the alt had to have power from batt to produce power not so in this case it was sending power to buse and self exciting I had a 5 amp breaker to the b lead.Now I have a toggle in line with 5 amp breaker and it shuts off alt.Check to make sure if you shut off master with engine running main buse shuts off.Im sure I'm the only dummy that's wired buse wrong not wanting to run two long #2 wires to rear of plane and it was exciting enough on ground would have been really exciting in the air.
Bob
 
B lead is the high current wire; you probably have the 5a breaker wired to the I terminal on an internally regulated alt.

What you described is common with IR alts.
 
You did notice the wire size notations?

I did, but perhaps I misread your intent. From the text preceeding the drawing, I thought you were disagreeing with Nuckolls' idea of leaving the 'fat wires' unprotected by fusing devices, and were offering an alternative.

A healthy starting battery could potentially overheat even a #2 wire if it doesn't burn away the fault (but Nuckolls says that will likely happen with a hard fault).
 
<Bob quotes the FARs:

Sec. 23.1357 Circuit protective devices.

...................

(d) If the ability to reset a circuit breaker or replace a fuse is essential to safety in flight, that circuit breaker or fuse must be so located and identified that it can be readily reset or replaced in flight
.>

This is an interesting conundrum. On a day VFR airplane, with mags (not EI), what circuit breaker is essential to safety in flight? If I lose my EFIS, there is a backup battery, unless the failure is internal to the EFIS itself. I can land safely without it in the daytime and I don't fly at night. If the main fuse/breaker blows/trips I would not want to be able to reset it. That indicates the possibility of a serious short and if one reset it the possibility of a fire. If that goes I will land and figure it out.

I think if there is a circuit whose failure causes a dangerous situation (as opposed to a reasonable increase in workload) then the system design needs to be revisited.

On the big ships when you do safety analysis you look at the effects of a failure and categorize them as Minor, Major, Hazardous an Catastrophic. I am setting up my system so that any common electrical failure will have at most Major consequences i.e. a slight increase in work load. If the consequence is higher, then I would add additional redundancy - another alt. or another battery, whatever it took so that for my mission (day VFR), the failures are all Minor or Major. If I decided to design for night or IFR capability, then obviously a given failure that was Major on a bright clear day could become Catastrophic (say if you lose the horizon) so that drives you to more redundancy. And I would not consider resetting a breaker as an acceptable risk mitigation for a failure. I would want to be able to consider that circuit lost and have a backup.
 
Would it be ok to use a reset-able 60 amp fuse such as the ones used in watercraft? They are a very slow response fuse and are priced about the same as an ANL fuse and holder.
https://www.amazon.ca/Blue-Sea-Syst...id=1542992085&sr=1-3&keywords=40+amp+blue+sea

Many folks use a Circuit Breaker, typically panel mounted. You can look back thru this thread for all of the discussions, pros/cons.
This Blue Sea Circuit Breaker is actually better than most as its specifications more closely resemble that of an ANL fuse if you compare trip time and interrupting capacity. It is also thermal only, not magnetic or thermal/magnetic. Thermal CB's would be better in this application and I am sure why they choose this for boating as well. I couldn't find the operating temperature tolerances.
That said, you should be able to get a 60A ANL with holder and cover for about half the cost of the Blue Sea CB, but probably not from Blue Sea.
ANL fuses have a very good proven track record and I see no advantage to using a CB, even a high quality unit like the Blue Sea.
 
I used two: One from the alternator feed to the main buss, and one for the electronics buss into the cockpit, installed on the right side of the firewall, together with current measurement shunts.

i-vt6hwnX-M.jpg
 
Thanks for the quick response. I did more reading and over a 60 deg. temp swing it is approx. 12%. I'm gonna go with the ANL... why reinvent the wheel!
 
Not to get into Fuse vs CB argument, but I am old school. I have a fancy 50 amp Circuit breaker in the panel, I can pull or reset. Would I reset it if it tripped ? Likely not. However I could pull it and it would be a visual indication I had a fault or short. My preference, that is all.

The fusible links or larger inline fuses does simplify the wiring slightly. However the not reinvention the wheel method would be a CB in the panel. With that said we are experimental. Do we need to follow the FAR for certified airplanes? We need to be safe and airworthy.
 
If you choose a CB, make sure it is a quality unit with a high interupt capacity. You don?t want a CB to fail closed.
 
Not to get into Fuse vs CB argument, but I am old school. I have a fancy 50 amp Circuit breaker in the panel, I can pull or reset. Would I reset it if it tripped ? Likely not. However I could pull it and it would be a visual indication I had a fault or short. My preference, that is all.

How do you protect the wire to the panel mounted circuit breaker?
 
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