Today's Message Index:
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1. 07:56 AM - Same rating for fuses and circuit breakers? (Mickey Coggins)
2. 11:28 AM - Re: Same rating for fuses and circuit breakers? (user9253)
3. 12:14 PM - Re: Re: Same rating for fuses and circuit breakers? (Art Zemon)
4. 12:41 PM - Re: Re: Same rating for fuses and circuit breakers? (Rick Beebe)
5. 12:53 PM - Re: Re: Same rating for fuses and circuit breakers? (Charlie England)
6. 01:51 PM - Re: Re: Same rating for fuses and circuit breakers? (Kelly McMullen)
7. 02:12 PM - Re: Same rating for fuses and circuit breakers? (user9253)
8. 02:34 PM - Re: Same rating for fuses and circuit breakers? (Robert L. Nuckolls, III)
9. 02:36 PM - Re: Re: Same rating for fuses and circuit breakers? (Robert L. Nuckolls, III)
10. 02:57 PM - Re: Re: Same rating for fuses and circuit breakers? (Robert L. Nuckolls, III)
11. 05:43 PM - Re: Re: Same rating for fuses and circuit breakers? (Robert L. Nuckolls, III)
12. 07:13 PM - Re: Re: Same rating for fuses and circuit breakers? (Sebastien)
13. 07:13 PM - Re: Re: Same rating for fuses and circuit breakers? (Dick Tasker)
Message 1
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Subject: | Same rating for fuses and circuit breakers? |
Hi,
I'm curious if we should use the exact same rating for fuses as are
recommended for circuit breakers.
I have all fuses with one CB as recommended by the AEC, and for most
devices they say something "protect with a 1 amp circuit breaker". My
understanding is that fuses are "faster", so more likely to blow in a case
where a CB might not have time to react - could be I have this wrong. Is
there a recommendation to use the exact same value of fuse as recommended
for circuit breakers, or should we increase the fuse size?
Thanks for any tips.
Mickey Coggins
Message 2
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Subject: | Re: Same rating for fuses and circuit breakers? |
Here is my opinion:
Use the same size.
Do not use fuses smaller than 3 amps. 3 amp fuses and larger are available from
Van's that glow when blown.
If a fuse nuisance blows for loads that have a high momentary current, use the
next larger size. Of course the wire must be able to carry the current.
The nice thing about fuses is that it is easy to change amp rating.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=483988#483988
Message 3
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Subject: | Re: Same rating for fuses and circuit breakers? |
Joe,
Why do you say not to use a fuse smaller than 3 amps? My backup
ASI/altimeter came with installation instructions calling for a 1 amp slow
blow fuse
<https://www.digikey.com/product-detail/en/littelfuse-inc/0218001.HXP/F2419-ND/777135>.
I splurged the $1.02 and installed it.
-- Art Z.
On Tue, Oct 23, 2018 at 1:52 PM user9253 <fransew@gmail.com> wrote:
>
> Here is my opinion:
> Use the same size.
> Do not use fuses smaller than 3 amps.
>
--
https://CheerfulCurmudgeon.com/
*"We do not see the world as it is. We see the world as we are."*
Message 4
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Subject: | Re: Same rating for fuses and circuit breakers? |
I think he means because you can't get the glow-when-blown fuses smaller
than 3amp. A 3amp fuse is able to protect a 24-gauge wire so I'm not
sure there's any reason to use smaller fuses. I don't have any wires
smaller than that in my plane anyway. That said, there's nothing wrong
with using smaller if a manufacturer calls for it and you don't mind
that it doesn't light up.
--Rick
On 10/23/2018 3:11 PM, Art Zemon wrote:
> Joe,
>
> Why do you say not to use a fuse smaller than 3 amps? My backup
> ASI/altimeter came with installation instructions calling for a 1 amp
> slow blow fuse
> <https://www.digikey.com/product-detail/en/littelfuse-inc/0218001.HXP/F2419-ND/777135>.
> I splurged the $1.02 and installed it.
>
> -- Art Z.
>
> On Tue, Oct 23, 2018 at 1:52 PM user9253 <fransew@gmail.com
> <mailto:fransew@gmail.com>> wrote:
>
> <fransew@gmail.com <mailto:fransew@gmail.com>>
>
> Here is my opinion:
> Use the same size.
> Do not use fuses smaller than 3 amps.
>
>
> --
> https://CheerfulCurmudgeon.com/
>
> /"We do not see the world as it is. We see the world as we are."/
Message 5
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Subject: | Re: Same rating for fuses and circuit breakers? |
I'll jump in, because that's one of my pet peeves. First, the mfgr of a
widget shouldn't be asking the end user to supply protection for their
device. Circuit protection protects circuits; not devices. If the mfgr
thinks their device needs a 1A fuse, it should be in the device. Ever
seen a piece of consumer or industrial electronics that came with a
requirement that you supply its fusing? (They tell you the *minimum*
size circuit needed; not a spec for device protection.) Second, a 1A
fuse isn't going to protect anything; the equipment will either die
before the fuse blows, or the fuse will be blowing needlessly on a more
or less random (possibly regular) basis. That's likely why Joe said not
to use any fusing under 3A; a policy I also use.
Charlie
On 10/23/2018 2:11 PM, Art Zemon wrote:
> Joe,
>
> Why do you say not to use a fuse smaller than 3 amps? My backup
> ASI/altimeter came with installation instructions calling for a 1 amp
> slow blow fuse
> <https://www.digikey.com/product-detail/en/littelfuse-inc/0218001.HXP/F2419-ND/777135>.
> I splurged the $1.02 and installed it.
>
> -- Art Z.
>
> On Tue, Oct 23, 2018 at 1:52 PM user9253 <fransew@gmail.com
> <mailto:fransew@gmail.com>> wrote:
>
> <fransew@gmail.com <mailto:fransew@gmail.com>>
>
> Here is my opinion:
> Use the same size.
> Do not use fuses smaller than 3 amps.
>
>
> --
> https://CheerfulCurmudgeon.com/
>
> /"We do not see the world as it is. We see the world as we are."/
---
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Message 6
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Subject: | Re: Same rating for fuses and circuit breakers? |
I seem to recall there is a reason that ammeters call for a 1 amp fuse
on each lead from the shunt. It certainly isn't for wire protection,
maybe to protect the meter movement.
On 10/23/2018 12:44 PM, Charlie England wrote:
> I'll jump in, because that's one of my pet peeves. First, the mfgr of a
> widget shouldn't be asking the end user to supply protection for their
> device. Circuit protection protects circuits; not devices. If the mfgr
> thinks their device needs a 1A fuse, it should be in the device. Ever
> seen a piece of consumer or industrial electronics that came with a
> requirement that you supply its fusing? (They tell you the *minimum*
> size circuit needed; not a spec for device protection.) Second, a 1A
> fuse isn't going to protect anything; the equipment will either die
> before the fuse blows, or the fuse will be blowing needlessly on a more
> or less random (possibly regular) basis. That's likely why Joe said not
> to use any fusing under 3A; a policy I also use.
>
> Charlie
>
> On 10/23/2018 2:11 PM, Art Zemon wrote:
>> Joe,
>>
>> Why do you say not to use a fuse smaller than 3 amps? My backup
>> ASI/altimeter came with installation instructions calling for a 1 amp
>> slow blow fuse
>> <https://www.digikey.com/product-detail/en/littelfuse-inc/0218001.HXP/F2419-ND/777135>.
>> I splurged the $1.02 and installed it.
>>
>> -- Art Z.
>>
>> On Tue, Oct 23, 2018 at 1:52 PM user9253 <fransew@gmail.com
>> <mailto:fransew@gmail.com>> wrote:
>>
>> <fransew@gmail.com <mailto:fransew@gmail.com>>
>>
>> Here is my opinion:
>> Use the same size.
>> Do not use fuses smaller than 3 amps.
>>
>>
>>
>> --
>> https://CheerfulCurmudgeon.com/
>>
>> /"We do not see the world as it is. We see the world as we are."/
>
>
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Message 7
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Subject: | Re: Same rating for fuses and circuit breakers? |
One reason is to keep the number of spare fuses to a minimum. Another reason is
that glow-when-blown fuses are not readily available at less than 3 amps. Wire
sizes commonly used to wire home-built airplanes can safely carry 3 amps.
But I am not going to argue with the equipment manufacture's recommendation.
Evidently your ASI/Altimeter does not have any internal protection. I should
not have wrote to not use less than a 3 amps fuse. It sure doesn't hurt to use
a smaller fuse than 3 amps. But I prefer not to.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=483993#483993
Message 8
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Subject: | Re: Same rating for fuses and circuit breakers? |
At 09:54 AM 10/23/2018, you wrote:
>Hi,
>
>I'm curious if we should use the exact same
>rating for fuses as are recommended for circuit breakers.
generally, yes
>I have all fuses with one CB as recommended by
>the AEC, and for most devices they say something
>"protect with a 1 amp circuit breaker".=C2 My
>understanding is that fuses are "faster", so
>more likely to blow in a case where a CB might
>not have time to react - could be I have this
>wrong.=C2 Is there a recommendation to use the
>exact same value of fuse as recommended for
>circuit breakers, or should we increase the fuse size?
I am suspicious of installation instructions
that call for 'downsized' protection with
respect to wire size.
This has the 'look and smell' of a design
gaff . . . albeit a minor one. I was taught
to make system integration and installation
completely independent of contemporary design
rules. In this example, suppose your electro-whizzy
needs 3.2A maximum at any time. You state that in
the specs . . . and stop there.
The system integrator would be expected to gravitate
to a 22AWG feeder on a 5A breaker . . . and in this
case, a 5A fuse (de-rated to 75% per recommended
practice) would be a good choice too. But if the
box goes all the way in the tail of a Hawker 4000,
the feeder might be upsized to 20AWG just to mitigate
voltage drop issues . . . and the system integrator
might well protect that wire with a 7A breaker.
Bottom line is, it shouldn't matter.
The 1A breaker requirement sounds like there may
be some design feature INSIDE the electro-whizzy
at risk for smoke due to some internal failure;
a risk mitigated by adjusting installation
requirements.
Is there risk associated with replacing a breaker
with a fuse? Maybe . . . breakers are a low slower
than fuses and the electro-whizzy may have some
transient draw that would irritate a fuse. If
you get nuisance trips, no big deal. Put the
next bigger fuse in.
But it WOULD be interesting to talk with
the engineer that built that feature into his/her
design . . . I mean, there ARE worse things you
could do . . . like let your electro-whizzy reset
during starter inrush events.
Bob . . .
Message 9
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Subject: | Re: Same rating for fuses and circuit breakers? |
At 02:44 PM 10/23/2018, you wrote:
>I'll jump in, because that's one of my pet peeves. First, the mfgr of a
>widget shouldn't be asking the end user to supply protection for their device.
Right on!
Bob . . .
Message 10
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Subject: | Re: Same rating for fuses and circuit breakers? |
At 03:49 PM 10/23/2018, you wrote:
>
>I seem to recall there is a reason that ammeters call for a 1 amp
>fuse on each lead from the shunt. It certainly isn't for wire
>protection, maybe to protect the meter movement
Yeah, first saw them do that on the 336/337 series
airplanes at the Pawnee plant. That was the
idea . . . but the fusing constant for a AGC1
(then a 3AG1) was such that a 5A flow of current
would take about 30 milliseconds to pop the fuse.
That 1 mA meter movement would be in trouble
a lot faster than that!
Don't know if anyone tested that decision
in the lab. There were some 50mV instruments
with lower resistance (maybe 10mA?). The
1 ohm fuse has about 200 mOhms of resistance.
Two fuses in series at 10 mA gives you a 4 mV
drop at full scale . . .
But I don't think anyone really paid much
attention to the readings anyhow . . . ammeters
are not really useful flight instruments.
Bob . . .
Message 11
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Subject: | Re: Same rating for fuses and circuit breakers? |
At 04:10 PM 10/23/2018, you wrote:
>
>One reason is to keep the number of spare fuses to a minimum.
Why would you carry spare fuses in the airplane?
Bob . . .
Message 12
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Subject: | Re: Same rating for fuses and circuit breakers? |
Ha! I know the answer to this one! In case you land away from base after
the fuse blows and you have repaired whatever caused the fuse to blow and
then want to get home.
On Tue, Oct 23, 2018, 17:47 Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
> At 04:10 PM 10/23/2018, you wrote:
>
>
> One reason is to keep the number of spare fuses to a minimum.
>
>
> Why would you carry spare fuses in the airplane?
>
> Bob . . .
>
Message 13
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Subject: | Re: Same rating for fuses and circuit breakers? |
To use when you get to your destination when you troubleshoot the problem.
Dick Tasker
Robert L. Nuckolls, III wrote:
> At 04:10 PM 10/23/2018, you wrote:
>>
>> One reason is to keep the number of spare fuses to a minimum.
>
> Why would you carry spare fuses in the airplane?
>
> Bob . . .
>
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