Fuse Size

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Fuse Size

Postby Capebuild » Mon Oct 04, 2021 12:59 pm

I'm trying to figure out what size fuse to use for a certain circuit.

On the circuit will be:
2 porch lights - draw .15 amps each (total .3 amps)
2 reading lights-draw .2 amps each (total .4 amps)
2 interior puck lights-draw .18amps each (total .36 amps)
2 galley puck lights-draw.18 amps each (total .36 amps)

for a grand total on the circuit (if all were on at the same time) = 1.42 amps

The wiring to all the fixtures is 14 AWG.

I was going to use a 5 amp fuse. Does that seem a reasonable size fuse for this circuit

thank you for the help.

John
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Re: Fuse Size

Postby DrewsBrews » Mon Oct 04, 2021 1:37 pm

5A seems appropriate for 14ga wire. Could go a little less based on your loads, but I think values less than 5A are harder to find and probably not necessary.
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Re: Fuse Size

Postby flboy » Mon Oct 04, 2021 2:07 pm

5a is fine, but remember the fuse is to protect the wiring. 14awg can handle up to 15A, but a smaller fuse is better in this case when you have a much lighter load.

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Re: Fuse Size

Postby MtnDon » Mon Oct 04, 2021 4:22 pm

flboy is correct about why we use fuses and breakers. They are used to keep the wiring from heating and melting the insulation, and maybe starting a fire. If you develop a short somewhere in the circuit any size fuse, up to the rated capacity for the wire, will blow and protect the wire. So theoretically any size fuse that is larger than the maximum possible current draw, but smaller than the maximum rating for the wire will work and be safe.

However, there is one other design factor that should be considered. This will usually only be a factor when maximum current draws must be considered, as in supplying power to some larger high current device(s), or if wire runs are long. In a low voltage (such as 12 VDC) we should also consider the wire length along with the maximum possible current use in order to keep the voltage drop down to 3% or less. If too much current is drawn through too long a wire the voltage sags, sometimes badly, and that can lead to problems.

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Re: Fuse Size

Postby Socal Tom » Mon Oct 04, 2021 4:25 pm

I agree with all that was said above, however I've been known to cheat, and stick with using only 10 and 15A fuses that way I reduce the number of spares to carry.
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Re: Fuse Size

Postby DrewsBrews » Tue Oct 05, 2021 7:36 am

Yeah always nice to try and condense the fuses down to a few of common values.. Makes it easy to keep a bunch of spares on hand for troubleshooting out in camp, and still have the option to hit up local stores for the common values.

Speaking of spares and troubleshooting. That reminds me it would be good to look around for all the screws used to attach/assemble things and be sure to at least have a screw driver on hand for all the head types.
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Re: Fuse Size

Postby MtnDon » Tue Oct 05, 2021 8:45 am

DrewsBrews wrote:
Speaking of spares and troubleshooting. That reminds me it would be good to look around for all the screws used to attach/assemble things and be sure to at least have a screw driver on hand for all the head types.


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Re: Fuse Size

Postby Capebuild » Tue Oct 05, 2021 3:54 pm

Thank you all for the replies and help. I only have 5 circuits with 3 of them being on 5 amp fuses. The other 2, my fridge and 12 volt receptacles, are on 10 amp circuits. The circuit I had asked about in my original post, I suppose I could use a 3 amp fuse for that (I went ahead and ordered some) but to start out, I'll use the 5 amp fuses and see how it goes.
Thanks again.

John
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