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Questions about circuit protection

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bakerocb

Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA

Posted: Sat Jan 02, 2010 9:13 am Post subject: Questions about circuit protection

1/2/2010



Hello Matthew Schumacher, You wrote: "I think I will just get fuse blocks 

per your recommendation for the reasons you mention, but also because 

problems with a fuse can be remedied in the air quickly and easily."



If you are thinking of replacing fuses in the air to trouble shoot and solve 

an electrical problem please think again. There are several disadvantages. 

Some are:



1) Your airplane's Operating Limitations (part of its airworthiness 

certificate) will require you to equip the aircraft in accordance with 14 

CFR 91.205 if you fly at night or IFR.



Paragraph 91.205 (c) (6) says: "One spare set of fuses, or three spare fuses 

of each kind required, that are accessible to the pilot in flight."



This means that, by regulation, if you design your airplane so that you have 

access to those fuse blocks in flight then you must also have available to 

you all those spare fuses while in flight. Do you want to create that burden 

/ nuisance / danger?



2) Trouble shooting an electrical system in flight by fumbling around to 

locate and then insert the appropriate fuse is not a good idea, particularly 

at night or IFR when you should be concentrating on flying the airplane.



So fuse blocks are a good idea, but where you locate them has some 

operational and safety implications. Please read some more of Bob Nuckolls' 

philosophy regarding electrical problems / failures in flight.



'OC' Says: "The best investment we can make is the effort to gather and 

understand knowledge."



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



Time: 07:42:35 PM PST US

From: Matthew Schumacher <schu(at)schu.net>

Subject: Re: AeroElectric-List: Questions about circuit protection.

First, thank you very much for looking at my stuff Bob.  I greatly

appreciate it and have donated to keep this list going...



..................................... big skip 

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



I know that fuses/breakers/fuselinks protect the wiring, what I was

missing was the part about problems with one component spreading to

others instead of being isolated.  I think I will just get fuse blocks

per your recommendation for the reasons you mention, but also because

problems with a fuse can be remedied in the air quickly and easily.



Thanks again,

schu

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bakerocb

Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA

Posted: Sun Jan 03, 2010 8:32 am Post subject: Questions about circuit protection

1/3/2009



Hello Again Matthew Schumacher, You wrote:



1) "Are you saying that if I put the fuses under the panel where they aren't 

accessible then my airplane will still meet 14 CFR 91.205 (c) and that I 

won't need to carry spares?"



Yes. That is exactly what the regulation is saying. If the pilot does not 

have access, while in flight,  to the location of fuses installed in the 

aircraft's electrical system then there is no 91.205 regulatory requirment 

to carry any spare fuses.



 2) "I would read "that are accessible to the pilot in flight" to mean that 

the fuse panel is accessible to the pilot,......."



That is correct.



3) "..........not the fusees since who cares if you can get to the fuses if 

you can't get to the panel."



Again correct. Your reasoning, and the reasoning of the regulation, is that 

if you cannot get access to the location of the fuses installed in the 

electrical system while in flight then there is no reason for the pilot to 

carry, and have access to, spare fuses while in flight.



Now the wise pilot would carry some spare fuses, as well as some other spare 

items or tools (which can be discussed at length), so that he may perform 

some limited trouble shooting / repair work if needed on the ground at some 

away from home location in order to get back to home base or some other 

location where he might be able to effect a more permanent repair.



'OC' Says: "The best investment we can make is the effort to gather and 

understand knowledge."



PS: If one is designing and manufacturing a 14 CFR Part 23 type certificated 

aircraft the regulations / requirements for fuse location in the aircraft's 

electrical system are found in

Part 23.1357 (d) which says:



"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."



But experimental amateur built aircraft are not required, per se, to comply 

with 14 CFR Part 23.



If we build our experimental amateur built aircraft's electrical system in 

accordance with the philosophy that things can fail and that we have a plan 

B back up that will allow graceful degradation and continued safe flight to 

an acceptable landing site then no fuse in our electrical system would be 

"essential to safety in flight".

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



Time: 11:09:21 AM PST US

From: Matthew Schumacher <schu(at)schu.net>

Subject: Re: AeroElectric-List: Questions about circuit protection

bakerocb(at)cox.net wrote:

 	  Quote: 	
		   If you are thinking of replacing fuses in the air to trouble shoot and

 solve an electrical problem please think again. There are several

 disadvantages. Some are:



 1) Your airplane's Operating Limitations (part of its airworthiness

 certificate) will require you to equip the aircraft in accordance with

 14 CFR 91.205 if you fly at night or IFR.



 Paragraph 91.205 (c) (6) says: "One spare set of fuses, or three spare

 fuses of each kind required, that are accessible to the pilot in flight."



 This means that, by regulation, if you design your airplane so that you

 have access to those fuse blocks in flight then you must also have

 available to you all those spare fuses while in flight. Do you want to

 create that burden / nuisance / danger?


	




Hold on, back the truck up.  Are you saying that if I put the fuses

under the panel where they aren't accessible then my airplane will still

meet 14 CFR 91.205 (c) and that I won't need to carry spares?



I would read "that are accessible to the pilot in flight" to mean that

the fuse panel is accessible to the pilot, not the fusees since who

cares if you can get to the fuses if you can't get to the panel.



schu

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