Question for confirmation. It is my understanding that fuse 18 (15A unswitched) feeds the red/black wire and fuse 19 (20A switched aux) feeds the blue wire. If this is the case, why are the wires labeled 10A and 3A do not exceed?
Fuse 18 and 19
- Thread starter Bargain Box
- Start date
OP
I confirmed with a meter I have the correct wires. Just wondering about the amperage limits. Fuse 19 also feeds the cigarette lighter which would explain the limit there. Just wondering why they limit the 15A unswitched circuit to 10A when the fuse is 15A...
OP
My confusion is that if the wire is only rated at 10A then the fuse should not exceed that. Fuses protect the wires, not the other way around. That is where my curiosity lies.
I would interpret the sticker as a limit for the circuit, not for the wire itself. And just because some UL or NEC table somewhere says a certain size wire is rated for a certain amperage doesn't mean it's always followed. It's common for manufacturers to perform their own testing in the actual configuration and use the smallest wire they can get to stay under the allowable temperature.
OP
Now you are talking my language! With no labels on the wire it's hard to know the limit of the wire. I'm guessing they are trying to protect the end user with that stamp.
It should also be noted that wires are not rated for a certain amperage based on size alone. They are rated for a certain amperage based on size (cross-section and material, actually) as well as length. Ampacity gets simplified to wire gauge, but copper is different than aluminum, stranded different than solid, and length also determines ampacity size it brings a different voltage drop/heat build up.
That said, auto manufacturers are generally conservative in this space, so I would be stunned to see too small a wire for the fuse. If, in reality, the circuit only carries 3 amps, then perhaps they would use a 22 gauge wire, but I would also expect to see a 3A fuse married to it, not a higher amp fuse and a label on the wire.
I don't recall the wires in question - do they provide power to any other items? If so, then you would need to subtract the rated vaue of the items already attached from the fuse amount to get the "remaining" amperage available to you.
Doug
That said, auto manufacturers are generally conservative in this space, so I would be stunned to see too small a wire for the fuse. If, in reality, the circuit only carries 3 amps, then perhaps they would use a 22 gauge wire, but I would also expect to see a 3A fuse married to it, not a higher amp fuse and a label on the wire.
I don't recall the wires in question - do they provide power to any other items? If so, then you would need to subtract the rated vaue of the items already attached from the fuse amount to get the "remaining" amperage available to you.
Doug
OP
This was the exact mindset driving this question. See my previous post about the 20A sharing the cigarette lighter. The 15A however does not appear to feed anything else. There is no real problem as I was just looking for a low amp place to tie in a circuit. Problem solved. Curiosity just got the best of me about the ratings on the wire tags.
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