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Bob.Bower(at)hdrinc.com
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 Posted: Mon Jul 21, 2014 12:56 pm Post subject: Z13 fusible link, circuit breaker, same circuit? |
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Something puzzles me . . .
Drawing Z-13/8 rev T dated 1/17/2014 shows both a 22AWG fusible link and a 5A circuit breaker between the main bus and terminal 5 of the Bat/Alt DC Power switch. When the Bat/Alt DC Power switch is closed and the alternator is making power, the 5A circuit breaker will open if the crowbar over voltage protection module connected to terminal 4 of the Bat/Alt DC Power switch, senses an over voltage condition and grounds the circuit. This functionality I understand.
The wire between the fusible link and the circuit breaker is called out as 18AWG, thus the four size smaller 22AWG fusible link makes sense to me. Three questions:
<![if !supportLists]>1. <![endif]>What is the function of the 22AWG fusible link in this circuit?
<![if !supportLists]>2. <![endif]>Shouldn’t the wire from the 5A circuit breaker to the Bat/Alt DC Power switch and the wire from the Bat/Alt DC Power switch terminal 4 to the voltage regulator terminal A also be 18AWG?
<![if !supportLists]>3. <![endif]>Alternatively, assuming the 20AWG wire is sufficient to carry the load, shouldn’t all wires in this circuit be 20AWG and the fusible link be 16AWG, i.e. 4 sizes smaller?
Thanks in advance for unpuzzling me.
[quote][b]
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JOHN TIPTON
Joined: 17 Sep 2006
Posts: 239
Location: Torquay - England
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| Posted: Mon Jul 21, 2014 1:49 pm Post subject: Z13 fusible link, circuit breaker, same circuit? |
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Just to clarify:
Question 3 : four sizes smaller than 20awg, is 24awg, not 16
John
Sent from my iPad
----x--O--x----
On 21 Jul 2014, at 09:55 pm, "Bower, Bob" <Bob.Bower(at)hdrinc.com (Bob.Bower(at)hdrinc.com)> wrote:
[quote] <![endif]--> <![endif]-->
Something puzzles me . . .
Drawing Z-13/8 rev T dated 1/17/2014 shows both a 22AWG fusible link and a 5A circuit breaker between the main bus and terminal 5 of the Bat/Alt DC Power switch. When the Bat/Alt DC Power switch is closed and the alternator is making power, the 5A circuit breaker will open if the crowbar over voltage protection module connected to terminal 4 of the Bat/Alt DC Power switch, senses an over voltage condition and grounds the circuit. This functionality I understand.
The wire between the fusible link and the circuit breaker is called out as 18AWG, thus the four size smaller 22AWG fusible link makes sense to me. Three questions:
1. What is the function of the 22AWG fusible link in this circuit?
2. Shouldn’t the wire from the 5A circuit breaker to the Bat/Alt DC Power switch and the wire from the Bat/Alt DC Power switch terminal 4 to the voltage regulator terminal A also be 18AWG?
3. Alternatively, assuming the 20AWG wire is sufficient to carry the load, shouldn’t all wires in this circuit be 20AWG and the fusible link be 16AWG, i.e. 4 sizes smaller?
Thanks in advance for unpuzzling me.
| Quote: |
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lectric-List"">http://www.matronics.com/Navigator?AeroElectric-List
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[b]
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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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| Posted: Tue Jul 22, 2014 9:55 am Post subject: Re: Z13 fusible link, circuit breaker, same circuit? |
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| Quote: | | What is the function of the 22AWG fusible link in this circuit? |
The wire (if very long) between the main power bus and the circuit breaker needs to be protected against short circuits. A fusible link provides this protection. The circuit breaker does not offer protection because short circuit current in this wire will not pass through the circuit breaker. A fuse can not be used because, in case of over voltage, a fuse will blow before the circuit breaker trips.
| Quote: | | Shouldn't the wire from the 5A circuit breaker to the Bat/Alt DC Power switch and the wire from the Bat/Alt DC Power switch terminal 4 to the voltage regulator terminal A also be 18AWG? |
No, 20 AWG wire can carry 5 amps allowed by the circuit breaker.
| Quote: | | shouldn't all wires in this circuit be 20AWG and the fusible link be 16 AWG, i.e. 4 sizes smaller? |
If the fusible link is made from smaller wire, it might mechanically break or it might burn open before the 5 amp breaker trips. So leave it at 22 AWG. The wire attached to the fusible link must be 4 sizes bigger, thus 18 AWG. 20 AWG is adequate downstream from the circuit breaker because it is protected by the circuit breaker.
(I edited my original posting.)
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