Cable Wire Resistance

gromike · May 22, 2024

So, I have been buying silicone insulated wire on Amazon for my battery builds. I'm wondering about the ampacity of these generic Amazon wires. I see there are 2 grades. For 10 awg that would be grade 1 at 49 amps, and grade 2 at 61 amps.
My question is how do you know what grade these wires are, or if they actually have the copper in them to carry the load they might be listed for. I'd be happy with the 10 awg silicone wire that I bought if it's truly rated for 49a (grade 1).

kuromaku · May 23, 2024

are you talking about wire graded by IEC-60137? i've only seen them applied to magnet wire used for magnetics windings, but if so, the grades are intended to be a controlling feature to determine insulation (voltage) breakdown resistance between windings. i guess as a side effect of the thicker insulations, one could push the temperature rating a bit, but lacking a technical datasheet for the wire you have, the easiest way would probably be to measure the OD with a micrometer and see if it meets the dimensions published for that gauge.

scianiac · May 23, 2024

First make sure you are buying copper wire, there is a lot of cheap aluminum wire being sold on amazon. Then yeah, just measure the wire bundle OD and compare.

The current ratings are all arbitrary in many ways, any "rating" is based on some standard that just picks variables. You can put way way more than 61 amps though 10awg and it will just get warmer and suffer more losses, the current at which the wire will fail, that is the silicone wire will decompose is insanely higher than that. So what are we really picking here, it's most likely acceptable losses. So take your average current and find the resistance in the system based on the wire size and length and find the voltage drop and in turn the power loss. Then you can get an idea of it's acceptable or not, if it's a high percentage of your power use the loss of efficiency means you probably want larger wires, if it's quite minimal you're good. You could do the same with peak current but we're often only there for a short time so total energy loss is not a ton.

jonyjoe303 · May 28, 2024

When I first started buying wire I was buying the cheapest which was usually copper clad wire CCA (they usually call it speaker wire), that wire corrodes easily, the one to buy is pure copper OFC wire (oxygen free wire) they call it welding wire or primary wire. Now I only buy OFC wire its heavier high quality, even the small 18 gauge wire I sometimes use , if its OFC will easily handle its rated amps.
The copper clad wire I wouldnt recommend for any high amp applications, I had many failed at the solder joints mostly from the corrosion.
I never notice grade 1 or 2 on any of the specs, all I go by is pure copper OFC and avoid any wire that is labeled as speaker wire.

Cali Yang · May 28, 2024

scianiac said:
First make sure you are buying copper wire, there is a lot of cheap aluminum wire being sold on amazon. Then yeah, just measure the wire bundle OD and compare.

The current ratings are all arbitrary in many ways, any "rating" is based on some standard that just picks variables. You can put way way more than 61 amps though 10awg and it will just get warmer and suffer more losses, the current at which the wire will fail, that is the silicone wire will decompose is insanely higher than that. So what are we really picking here, it's most likely acceptable losses. So take your average current and find the resistance in the system based on the wire size and length and find the voltage drop and in turn the power loss. Then you can get an idea of it's acceptable or not, if it's a high percentage of your power use the loss of efficiency means you probably want larger wires, if it's quite minimal you're good. You could do the same with peak current but we're often only there for a short time so total energy loss is not a ton.

Very good answer

Cable Wire Resistance

gromike

1 kW

kuromaku

100 mW

scianiac

1 kW

jonyjoe303

100 W

Cali Yang

1 mW

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