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art(at)zemon.name
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 Posted: Thu Mar 03, 2016 3:03 pm Post subject: Selecting a Fuse |
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This is good stuff. I appreciate all of the opinions.
Here is a "fer instance:" I have an autopilot servo which averages 0.9A and, at max torque, draws 1.71A. It sounds like I might select a fuse this way:
- I need 10' of wire.
- The manufacturer recommends 18-20 AWG wire. Using 20 AWG wire, 1.7A (at) 14V will drop 0.3V in 10'. That seems OK to me.
- Then, rather than fuse to the max current that 20 AWG can carry, I might try a 2A fuse. If that nuisance blows, I could try either 3A or 2A slow-blow.
Reasonable?
Thanks,
-- Art Z.
On Thu, Mar 3, 2016 at 8:26 AM, user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:
| Quote: | --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>
I agree with kenryan. Fuse sizes in a table are the maximum fuse sizes. There is nothing wrong with using a smaller fuse size as long as it does not nuisance blow. If the wire size is increased to reduce voltage drop over a long distance, the fuse size does not need to be increased. |
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http://CheerfulCurmudgeon.com/"If I am not for myself, who is for me? And if I am only for myself, what am I? And if not now, when?" Hillel
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JimT
Joined: 27 Feb 2006
Posts: 22
Location: Auburn, ME
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| Posted: Thu Mar 03, 2016 3:11 pm Post subject: Selecting a Fuse |
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The next question is how many types of wire do you want to buy? A roll of 18ga will serve most purposes,some as overkill. It is minimally stiffer to handle.
The weight increase for the plane is neglibable. Decreases the number of connecter sizes to buy
Jim Timoney
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lm4(at)juno.com
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| Posted: Thu Mar 03, 2016 3:30 pm Post subject: Selecting a Fuse |
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I'll take a shot at this.The N. electrical code requires you to to size the wire to 125% of its ampacity and then size the fuse at 80% of that, or less. Again its over size the wire for the load and under size the fuse to protect the wire. If you want to protect the appliance, put protection at the appliance.
Larry
On Mar 3, 2016, at 6:02 PM, Art Zemon wrote:
| Quote: | This is good stuff. I appreciate all of the opinions.
Here is a "fer instance:" I have an autopilot servo which averages 0.9A and, at max torque, draws 1.71A. It sounds like I might select a fuse this way:
- I need 10' of wire.
- The manufacturer recommends 18-20 AWG wire. Using 20 AWG wire, 1.7A (at) 14V will drop 0.3V in 10'. That seems OK to me.
- Then, rather than fuse to the max current that 20 AWG can carry, I might try a 2A fuse. If that nuisance blows, I could try either 3A or 2A slow-blow.
Reasonable?
Thanks,
-- Art Z.
On Thu, Mar 3, 2016 at 8:26 AM, user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:
| Quote: | --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>
I agree with kenryan. Fuse sizes in a table are the maximum fuse sizes. There is nothing wrong with using a smaller fuse size as long as it does not nuisance blow. If the wire size is increased to reduce voltage drop over a long distance, the fuse size does not need to be increased. |
--
http://CheerfulCurmudgeon.com/"If I am not for myself, who is for me? And if I am only for myself, what am I? And if not now, when?" Hillel
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art(at)zemon.name
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| Posted: Thu Mar 03, 2016 4:19 pm Post subject: Selecting a Fuse |
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So actually reading AC43-13 was illuminating.
| Quote: | | 11-48. DETERMINATION OF CIRCUIT BREAKER RATINGS. Circuit protection devices must be sized to supply open circuit capability. A circuit breaker must be rated so that it will open before the current rating of the wire attached to it is exceeded, or before the cumulative rating of all loads connected to it are exceeded, whichever is lowest. A circuit breaker must always open before any component downstream can overheat and generate smoke or fire. |
I added the emphasis.
It looks like using a 2A breaker to protect a 1.7A device on a 20 AWG wire can be justified by AC43-13.
Cheers,
-- Art Z.
--
http://CheerfulCurmudgeon.com/"If I am not for myself, who is for me? And if I am only for myself, what am I? And if not now, when?" Hillel
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