OV protection, do I need one?

I am getting a 60A B&C alternator and their (external) regulator that goes with it which has a built in OV protection. I asked B&C if I should install any other crowbar/shunt for OV protection and they said not needed with their alternator but recommended with their small backup alternator (I think permanent magnet one) so I thought to check to see others are doing in this regard?
Also, looking for a 70A pull/push master CB that is reasonable in cost if anyone has any source or suggestion. I have found a 70A at spruce that is very inexpensive but it is not pull/push type.

All thoughts and suggestions are welcomed.

I would not add extra overvolt protection. I use a 40 amp CB for my system as I cannot imagine my 70 amp alternator ever having to produce that much current.

Their external regulator for the big alt has OV protection built in. If they say to install OV protection in addition to their PM alt, then I'd do it; that's an indication that the regulator for it does *not* have it built in.

Are you asking for a CB for your *master*, or for the alternator feed line? If it's for the alternator B-lead, a CB is not the best choice. There's no need to control that line with a CB. The protection for that line should be on the battery end, and the only time protection would activate would be a catastrophic short in either the wire or inside the alternator. With proper installation, both are so unlikely that a more or less permanent method would be better; either a high current fuse, or (in my opinion) better, a fusible link soldered in the battery end of the B-lead.

Here's the logic: The B-lead should be big enough to handle everything the alternator is capable of delivering, so you're not protecting the wire from the alternator. However, it'll never be big enough to survive the full current from the battery.

Charlie

Upgrade

flyinga said:

I would not add extra overvolt protection. I use a 40 amp CB for my system as I cannot imagine my 70 amp alternator ever having to produce that much current.

Click to expand...

An EarthX battery will draw as much as the alternator can produce. Keep that in mind if you ever decide to upgrade.

Voltage and current aren't the same thing.. You can't use a CB to protect for an over voltage situation.

JohnInReno said:

An EarthX battery will draw as much as the alternator can produce. Keep that in mind if you ever decide to upgrade.

Click to expand...

I was just thinking the same thing. If you have a subscription to Kitplanes there was an article about undersized alternator breaker causing an issue (December 2017 issue?)

Standard wire-wound alternators are shut down during an overvoltage event by shorting the excitation input, popping the field CB, and removing the excitation. PM alternators typically have a "controller" instead of a regulator. The controller also provides rectification of the 3 phase output of the alternator. It does not provide OV protection. The output from the controller to the aircraft bus goes through a relay, and this relay is opened by the crowbar OV module. Sometimes a PM alternator is shut down by opening 2 of the 3 phases in the output from the alternator, again with a relay. Check out the B&C wiring diagrams on their website, and also Bob Nuckolls' "Aeroelectric Connection".

I appreciate all the input.
For clarity, I had a two part question. The OV protection which B&C told me that I won't need since it is already provided by the external regulator was for voltage and the 60A CB is my master which I like to be able to completely shut down all the electrical system in an emergency situation so each (OV and CB) will serve a different purpose.

JohnInReno said:

An EarthX battery will draw as much as the alternator can produce. Keep that in mind if you ever decide to upgrade.

Click to expand...

Truth. I recently installed an EarthX ETX900 and my 70 amp alternator will show mid-40 amp charge rates at 900-1000 rpm warming up right after start for the first minute or so. The battery will take just about all you want to give it.

Mehrdad,

Unfortunately, it's not clear (at least to me) where that 60A CB will be located in the circuit.

Here are some thoughts. For a 'typical' (whatever that means...) installation, you need a high current master contactor (relay) controlled by your master switch. By high current, I mean an intermittent duty rating of at least a couple hundred amps, because your starter current will flow through that relay before it goes to the starter contactor. This master contactor is your emergency disconnect. Adding another device in that line is simply adding another failure point. Now, you can make a case for adding current protection to that wire, but the certified world almost never has it, and the percentages of problems caused by this is vanishingly small. And note that if you *do* add a pullable CB to that feed, coming into the cockpit, it won't protect the run from the battery to the CB in the instrument panel.

There are other ways to configure the system that are valid, but the above has stood the test of time counted in decades.

If this doesn't make sense, perhaps you could share more about what you're trying to achieve.

Have you obtained and read through the Aeroelectric Connection book? If not, stop. Do not pass go. Get the book, read it, and only then start your wiring process.

I normally try to avoid telling people there's only one way to do something. But having watched some of the advice given on this forum about electrical stuff, I can tell you that it is about as reliable as political info on Facebook. If you don't already have some basic background in herding electrons, you are at great risk depending only on this forum for electrical advice. I'll be the 1st to tell you I don't know everything about electrons, but I have had several previous lives making my living at it and a lot of advice here is just bad, and some demonstrates complete ignorance. Sorry to be so blunt, but someone needs to say it.

Charlie

Bavafa said:

I am getting a 60A B&C alternator and their (external) regulator that goes with it which has a built in OV protection. I asked B&C if I should install any other crowbar/shunt for OV protection and they said not needed with their alternator but recommended with their small backup alternator (I think permanent magnet one) so I thought to check to see others are doing in this regard?
Also, looking for a 70A pull/push master CB that is reasonable in cost if anyone has any source or suggestion. I have found a 70A at spruce that is very inexpensive but it is not pull/push type.

All thoughts and suggestions are welcomed.

Click to expand...

I believe in Bob Nuckols' designs.

But who am I? And who is anyone else on a forum?... that's a problem. But we do know who Bob is.

I'm not knowledgeable about Vertical Power so I can't speak to that but if you are not using Vertical Power and you are planning B&C 60A main and 8A auxiliary alternators, what could be better than Z13/8? (Except replacing the main alternator's Ford regulator with B&C and deleting the main alternator's crowbar since it is incorporated into the B&C regulator.)

Z13/8 show's a crowbar on the 8A auxiliary alternator and it's a small cost at $40.

That CB in the main alternator's B lead? Bob says no; use a current limiter.

https://drive.google.com/file/d/19vu8KCJ8UNvPf6yP5PMRef2DWwaqTbOp/view

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

Begin rant...

People say I built it this way and that way and never had a problem; but that's anecdotal; you can cross the street without looking and say that.

I see a lot of advice and proposals on this forum that make me think electrical architecture is a big problem for the safety of EAB aircraft, expecially if they are electrically dependent. If you are using self-powered ignition and an engine-mounted fuel pump you can have an electrical problem and at least the engine will keep running.

Communicating electrical proposals using words alone is asking for misunderstandings with important consequences.

BTW, anecdotally, but in more than one instance in my limited experience, I have seen loose wire crimps, which of course could bring down an electrically dependent airplane. I believe not only electrical design but also execution are opportunities to improve EAB safety.

We know who Bob Nuckols is. And we know he speaks Failure Mode and Effects Analysis. So isn't it wise to know what we don't know and consult an expert, for free, in Aeroelectric Connection? As far as I can tell, the FMEAs, or similar, behind Bob's circuits are not available so if you make changes you may create failure modes that are surprising, unknown, and bad.

... end rant

johnbright said:

So isn't it wise to know what we don't know and consult an expert, for free, in Aeroelectric Connection? As far as I can tell, the FMEAs, or similar, behind Bob's circuits are not available so if you make changes you may create failure modes that are surprising, unknown, and bad.

... end rant

Click to expand...

Right....

and if anyone, ever, for any reason, wants to change anything, that's bad and they shouldn't do that. That's why we still drive flintstone vehicles, right?

Bob's a brilliant guy, don't get me wrong - but he's not the only one and he didn't come down the mountain with Moses. There are other ways that work too. Don't get me wrong, I'm not picking on Bob here, or you or anyone else - just the idea that we should "always do it that way because it's always been done that way." That's a pile of something that will just show up as asterisks here.

Greg,

I suspect you're misinterpreting what we are saying. By way of analogy:

Let's say I didn't know how to fly. Now, there's a well established body of knowledge on flying and learning how to fly, along with people who are both knowledgeable and experienced to help me learn. And there are various methods of actually learning. Should I just elect to learn how to fly alone, or consult someone who has no clue about what makes a plane fly?

Nothing wrong with trying something different, but this stuff can be life/death. If one wants to try new stuff, it would pay to begin with a foundation of what does and doesn't work.

Charlie
(Mazda Renesis FWF in progress. Different enough?)

rv7charlie said:

Mehrdad,

Unfortunately, it's not clear (at least to me) where that 60A CB will be located in the circuit.

Here are some thoughts. For a 'typical' (whatever that means...) installation, you need a high current master contactor (relay) controlled by your master switch. By high current, I mean an intermittent duty rating of at least a couple hundred amps, because your starter current will flow through that relay before it goes to the starter contactor. This master contactor is your emergency disconnect. Adding another device in that line is simply adding another failure point. Now, you can make a case for adding current protection to that wire, but the certified world almost never has it, and the percentages of problems caused by this is vanishingly small. And note that if you *do* add a pullable CB to that feed, coming into the cockpit, it won't protect the run from the battery to the CB in the instrument panel.

There are other ways to configure the system that are valid, but the above has stood the test of time counted in decades.

If this doesn't make sense, perhaps you could share more about what you're trying to achieve.

Have you obtained and read through the Aeroelectric Connection book? If not, stop. Do not pass go. Get the book, read it, and only then start your wiring process.

I normally try to avoid telling people there's only one way to do something. But having watched some of the advice given on this forum about electrical stuff, I can tell you that it is about as reliable as political info on Facebook. If you don't already have some basic background in herding electrons, you are at great risk depending only on this forum for electrical advice. I'll be the 1st to tell you I don't know everything about electrons, but I have had several previous lives making my living at it and a lot of advice here is just bad, and some demonstrates complete ignorance. Sorry to be so blunt, but someone needs to say it.

Charlie

Click to expand...

Hi Charlie,
I appreciate the good advice here. Somehow either I am not writing clearly here or things get misinterpreted (not by you necessarily)

The 70A CB that I am planning on installing would be between the alternator and the rest of the electronic, including the battery. Essentially, I want to limit the draw from the alternator, either by the battery, avionics or combination of both. I don’t know if that is a smart/recommended or simply needed precaution but this is what I had in my old plane and was recommended then. It was a way of protecting the draw from the alternator by the combination of electronics in the plane. I also had a 40A “avionics CB” which was feeding my avionics bus but I am eliminating that this time as my logic tells me that each of the avionics is on its own CB and the combination of all are below my wiring size.
If it helps explaining my understanding of using CB, I am aiming to protect the wiring rather than the equipment therefore I want to limit how much current can flow thru each given size wire.

If you see a flaw in my logic or have a recommendation, I love to hear it.

BTW, I am planning on only the one alternator and not a backup/standby alternator.

johnbright said:

I believe in Bob Nuckols' designs.

But who am I? And who is anyone else on a forum?... that's a problem. But we do know who Bob is.

I'm not knowledgeable about Vertical Power so I can't speak to that but if you are not using Vertical Power and you are planning B&C 60A main and 8A auxiliary alternators, what could be better than Z13/8? (Except replacing the main alternator's Ford regulator with B&C and deleting the main alternator's crowbar since it is incorporated into the B&C regulator.)

Z13/8 show's a crowbar on the 8A auxiliary alternator and it's a small cost at $40.

That CB in the main alternator's B lead? Bob says no; use a current limiter.

https://drive.google.com/file/d/19vu8KCJ8UNvPf6yP5PMRef2DWwaqTbOp/view

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

Begin rant...

People say I built it this way and that way and never had a problem; but that's anecdotal; you can cross the street without looking and say that.

I see a lot of advice and proposals on this forum that make me think electrical architecture is a big problem for the safety of EAB aircraft, expecially if they are electrically dependent. If you are using self-powered ignition and an engine-mounted fuel pump you can have an electrical problem and at least the engine will keep running.

Communicating electrical proposals using words alone is asking for misunderstandings with important consequences.

BTW, anecdotally, but in more than one instance in my limited experience, I have seen loose wire crimps, which of course could bring down an electrically dependent airplane. I believe not only electrical design but also execution are opportunities to improve EAB safety.

We know who Bob Nuckols is. And we know he speaks Failure Mode and Effects Analysis. So isn't it wise to know what we don't know and consult an expert, for free, in Aeroelectric Connection? As far as I can tell, the FMEAs, or similar, behind Bob's circuits are not available so if you make changes you may create failure modes that are surprising, unknown, and bad.

... end rant

Click to expand...

Hi John,
I am not planning on using the 8A standby alternator. If I mistakenly gave that impression, my bad.

I am surprised no one has mentioned this, so I will.

In the Aeroelectric, the only recommended protection, on the high current feeder from a non PM Alternator - is an ANL current limiter sized for your alternator. These can be thought of as very slow blow fuses. You will not get nuisance trips from them. If they go you have a real problem somewhere. You can reference Bob's Z13 drawing as one example that probably mimics the exact B&C hardware you describe.

These are meant to be in close proximity to all your high current feeders and the battery on the forward side of the firewall. You would use this in place of your proposed 70A circuit breaker. As others have pointed out, you would not want to bring such a high amperage feeder to your panel unprotected. The current limiter will probably outlast the airplane without ever tripping.

B&C sells them but I don't think they sell the mini versions of them that are available from lots of places on the internet. You need the holder and the current limiter. They come in all kinds of amperages and a 60 amp will work fine.

I hope this adds to the discussion without any confusion. While there are always other ways to do things, like others here, I also highly recommend the Aeroelectric drawings and articles.

rv7charlie said:

Let's say I didn't know how to fly. Now, there's a well established body of knowledge on flying and learning how to fly, along with people who are both knowledgeable and experienced to help me learn. And there are various methods of actually learning. Should I just elect to learn how to fly alone, or consult someone who has no clue about what makes a plane fly?

Click to expand...

I know of at least 2 guys who did exactly that, yes. And no, I'm not saying we all should do that - but I don't like being force-fed the idea that it's the only way.

Bob,

That's what I was saying in post #3. I have an aversion to calling them 'current limiters'; that implies a completely different function. FWIW, I prefer a fusible link in that application. It avoids mounting a fuse holder, and at least eight extra joints in the alternator line with the insertion of the fuse & holder. The link can simply be the 1st 4" of the alternator B-lead (on the battery end, of course).

Charlie

Bavafa said:

Hi Charlie,
I appreciate the good advice here. Somehow either I am not writing clearly here or things get misinterpreted (not by you necessarily)

The 70A CB that I am planning on installing would be between the alternator and the rest of the electronic, including the battery. Essentially, I want to limit the draw from the alternator, either by the battery, avionics or combination of both. I don?t know if that is a smart/recommended or simply needed precaution but this is what I had in my old plane and was recommended then. It was a way of protecting the draw from the alternator by the combination of electronics in the plane. I also had a 40A ?avionics CB? which was feeding my avionics bus but I am eliminating that this time as my logic tells me that each of the avionics is on its own CB and the combination of all are below my wiring size.
If it helps explaining my understanding of using CB, I am aiming to protect the wiring rather than the equipment therefore I want to limit how much current can flow thru each given size wire.

If you see a flaw in my logic or have a recommendation, I love to hear it.

BTW, I am planning on only the one alternator and not a backup/standby alternator.

Click to expand...

Mehrdad,

I'd respectfully submit that you're starting with the wrong premise. You don't need to protect the the electronics in your plane from excess *current*. Barring a failure in a device, it will only draw the current it needs; example: your cell phone charger in your car will only draw an amp or so from the battery, even though the battery can supply hundreds of amps. You only need to protect *the wire* from the battery if something goes wrong and too much current is asked to flow through the wire. Over *voltage* is a different animal, but we've already discussed the fact that B&C regulators have OV protection built in.

Some things to remember:
1. Standard field-wound alternators like almost everyone uses (B&C, automotive, etc) are self-limiting. You can't damage them by overloading them.

2. Alternator B-lead wire (the wire that feeds current from the alternator into the system) should be sized big enough to handle all the current the alternator can deliver.

3. With 1 & 2 in mind, you don't need to protect the alternator from anything, and you don't need to protect the wire from the alternator.

4. (This one can be hard to grasp, at first) You *do* need to protect the B-lead wire *from the battery*. Since the battery can supply hundreds of amps, and the B-lead will likely handle only 60-80 amps (depending on size/length), it should have suitable protection (fat fuse/ 'current limiter'/ fusible link) on the end that's closest to the battery. This protects the wire if you somehow have a short to ground on that wire somewhere along its path to the alternator's B terminal. To be redundant, that is the *only* reason to protect that wire.

5. (This one can also be hard to grasp) The main feed into the cockpit from the Master Contactor is typically protected by the contactor itself. Now, I'm not saying the contactor will automatically open if there's an overload. But the FAA here in the USA has had regulations in place for decades that allow the pilot to be the 'manually activated protection' for overloads on that feed line. The vast majority of certified a/c built in the USA in the last 40-50 years use this scheme. So if you have the typical master contactor near your battery, controlled by a master switch on your instrument panel, the FAA would be happy with your protection method for the wire coming into the cockpit. You're free to add a CB if you wish, but remember, it will not add any protection for the wire between the contactor & the CB, and it will not do anything to protect your avionics from the alternator. The only damage the alternator can do is from over*voltage*, which is handled by the protection built into the B&C regulator.

I have to ask again, do you have a copy of the Aeroelectric Connection book? That is the shortest path I know to getting up to speed on electrical stuff in your plane.

Charlie

rv7charlie said:

Mehrdad,

I'd respectfully submit that you're starting with the wrong premise. You don't need to protect the the electronics in your plane from excess *current*.
Charlie

Click to expand...

Please see my earlier post:
If it helps explaining my understanding of using CB, I am aiming to protect the wiring rather than the equipment therefore I want to limit how much current can flow thru each given size wire.
Are we not saying the same thing?

Can some one please explain to me the difference between a current limiter and a CB? Would a current limiter throttle the current to only specific max allowed without blowing/popping like a CB does?

Bavafa said:

Please see my earlier post:
If it helps explaining my understanding of using CB, I am aiming to protect the wiring rather than the equipment therefore I want to limit how much current can flow thru each given size wire.
Are we not saying the same thing?

Click to expand...

Not sure.

The fat CB will do nothing at all for the smaller wires that run from your avionics bus to the individual radios, etc. Protection for those wires is handled by individual fuses or CBs in the bus, sized for each smaller wire.

Current path:

Battery>master contactor>wire to cockpit>fat CB>wire to avionics bus>bus with multiple fuses or CBs for avionics

Following that path, note that the only wire your fat CB will protect is the one between the CB and the avionics bus, which is already protected by the master contactor, using the pilot's finger on the master switch.

If you delete the fat CB, you get:

Battery>master contactor>wire to avionics bus>bus with multiple fuses or CBs for avionics

which for all practical purposes, is the same protection. The only thing you lose is *automated* protection from a fault in the wire between the CB and the avionics bus. Your gain is eliminating a bunch of failure points and one less very expensive CB.

If you really want automated protection on that feeder wire, add a fat fuse ('current limiter') or a fusible link at the output of the master contactor:

Battery>master contactor>fusible link>wire to avionics bus>bus with multiple fuses or CBs for avionics

This protects the feeder all the way from contactor to bus.

Charlie

Speaking of CB, fuses, fusable links, contactors, Mr. Nuckolls? figure Z-17 has no master contactor, just a switch, which is rated for 20 amps. My understanding is that a simple switch is deemed sufficient because Z-17 is designed for systems where the power draw can never exceed the rating of the switch. So, depending on the the system draw, you may or may not need a contactor/relay between the battery/alternator and the power consumers (other than the starter, of course).
Z-17 is fed by an 8 amp PM alternator, but I do not believe this is the determining factor for whether or not to use a master contactor or a switch.
Am I correct?

Bavafa said:

Please see my earlier post:
If it helps explaining my understanding of using CB, I am aiming to protect the wiring rather than the equipment therefore I want to limit how much current can flow thru each given size wire.
Are we not saying the same thing?

Can some one please explain to me the difference between a current limiter and a CB? Would a current limiter throttle the current to only specific max allowed without blowing/popping like a CB does?

Click to expand...

A current limiter (as used in this context) will not actually limit current.

A CB (circuit breaker) is a cockpit-resettable device that will trip when the current flowing through it exceeds a certain point. It does not care about voltage, only current. This is not to be confused with an overvoltage (crowbar) circuit designed to drop out the field on a malfunctioning alternator - that circuit USES a circuit breaker (on the field current) but has quite a bit more going on as well.

A fuse, or fusible link, or current limiter (as used in this discussion) are all the same thing in somewhat different forms - a physical piece of conductor that will burn itself in two if the current exceeds a certain value. Again, this device does not care about voltage, only total current. Fuses can be, but are not always, cockpit replaceable. Normally the "current limiter" type fuses discussed here are mounted on the hot side of the firewall and are not accessible in flight. None of these devices will actually control the amount of current flowing through them - they will only self-destruct if the current exceeds the critical value.

A true "current limiter" is a different animal entirely and is not used on aircraft, except for specific purposes like LED and HID light power supplies.

Kalibr said:

Speaking of CB, fuses, fusable links, contactors, Mr. Nuckolls’ figure Z-17 has no master contactor, just a switch, which is rated for 20 amps. My understanding is that a simple switch is deemed sufficient because Z-17 is designed for systems where the power draw can never exceed the rating of the switch. So, depending on the the system draw, you may or may not need a contactor/relay between the battery/alternator and the power consumers (other than the starter, of course).
Z-17 is fed by an 8 amp PM alternator, but I do not believe this is the determining factor for whether or not to use a master contactor or a switch.
Am I correct?

Click to expand...

You're correct. There are some certified a/c that are wired the way you describe. But they are typically quite simple with very little in the way of electrical loads.

Some builders, especially ones who are using electrically dependent engines and wish to minimize battery consumption if there's an alternator failure, have used that technique. The master contactor's coil can draw one to two amps continuous; a not-insignificant load. I used a contactor for my general avionics needs, but the engine bus (electrically dependent engine) is wired:

battery>fusible link>hi-current switch>engine bus
(The engine bus can also be powered from the avionics bus, as a backup to the switched feed.)

But most a/c these days need a simple, but higher current, supply than can [not] be easily designed without that master contactor. If the battery is in the back and the motor is in the front, you need some way to disconnect that 'fat wire' near the battery in an emergency. Evolution has picked the master contactor as the best compromise in most installations.

Charlie, thanks!

What the B-lead CB is for-

The proper place for the CB rated to carry the alternator’s full output is as near as possible to the point where the B-lead connects to the main bus. Its primary purpose is to protect everthing else on your main bus from direct shorts that might occur in the cable between it and the alternator itself, or internal shorts within the alternator. Even if you shut down the field, that cable remains hot with battery power all the way to, and to a degree into, the alternator anytime the master switch is on. One very good alternative is to use a circuit interruptor(big-*** fuse) located right at the master contactor output side. This keeps all wiring between the alternator and bus forward of the firewall, but it has to be physically replaced if it ever blows.

rv7charlie said:

Not sure.

The only thing you lose is *automated* protection from a fault in the wire between the CB and the avionics bus. Your gain is eliminating a bunch of failure points and one less very expensive CB.

Charlie

Click to expand...

Bingo... this is actually what I am aiming to have, *automated* as I would not be able to detect the problem and mitigate it in time to protect the wire and possible start of a fire.

I believe now we are on the same page.

Not yet.

If you want automated protection (for any wire; not just this one), the protection needs to be at the source.

The alternator B lead protection needs to be where ever it ends up at/near the firewall (master contactor, etc).

If you want to protect the wire between the master contactor and cockpit electronics, that protection needs to be at the output of the master contactor. Using a circuit breaker in the panel doesn't meet that requirement, since it leaves the run between the contactor and the circuit breaker unprotected.

If this isn't clear, then either draw it out, or mock it up using string and something to represent the battery and each component that will be in the system. Place your finger on various places on the string (representing wire) and pretend your finger is a short to ground. Look back from that point toward the battery and find the protection.

Charlie

Charlie,
Once I get a chance, I will draw it to confirm but for now and in short and barrowing your method:
From Battery -> master solenoid -> bottom pin of 70A CB -> bottom Pin of 70A CB to continue main bus
From Alt -> upper pin of 70A CB

With this scenario, once I turn up my master, I get juice to my bus... as soon as the alternator is spinning, the juice is added to the bus and battery.

I can isolate the battery by turning of master (not automatic thru a CB)
I can isolate the alt by pulling the 70A CB (automatic thru the CB) or simply pulling it

The 70A CB main job is to protect the wire that runs from the Alt to the bus

See if that makes any sense.

It'll work. But if this is an RV, and the battery is on the firewall, then the master contactor is a lot closer to the alternator than the instrument panel. A more conventional method of routing the B lead is to tie the B lead to the load side of the master contactor. If you place a big fuse (commonly called 'current limiter') or a fusible link between that terminal and the B lead, you've got your protection for the B lead.

Here's the logic for placing it there. You've saved as much as several feet of relatively heavy wire, required to get past the firewall and to the instrument panel. And since this is such a high reliability area of the electrical system, the need to access the protection for that line while in flight is virtually non-existent. If that protection 'blows', there's a serious problem that can only be dealt with on the ground.

But yes, your plan will work.

Charlie