AWG cable current rating without voltage/length indication - Page 1
Forum section: electronics / beginners

author: Yaroooo
author_rank: Regular Contributor
timestamp: October 20, 2021, 09:09:49 am
content: Hello,I'd like to ask why on most table is indicated only current rating. I mean, doesn't cable dissipate power that is a relation between current and voltage? Also is missing length of the reference cable.In example, on Reference image there's AWG 10 rated for 15A. At which voltage (maybe 110 or 220?) and length (maybe 1m?) ?And is this an indication of when cable gets hot or melts?Reference:

author: Yaroooo
author_rank: Regular Contributor
timestamp: October 20, 2021, 09:23:24 am
content: To my question about cables, I want to add a question about connectors.This one for example:AM-1009Lhttps://www.tme.eu/Document/2be4e3e05d9ba90946bd61c466eee7d8/AM-1009L%20SPEC.pdfHave a rated current of 70A , I suppose at 500V right? Since it's rated voltage.While rated current mean about 30° of temp. increase, what max current mean?

author: elekorsi
author_rank: Regular Contributor
timestamp: October 20, 2021, 09:49:05 am
content: Current capacity has nothing to do with voltage. The cable will have the same resistance at 24V or at 230V. Total power losses on the cable can be calculated from current and resistance.Lenght is important if you want to calculate the voltage drop. You select the cable by:-current carying capacity (protection elements)-allowed voltage drop at max current-short circuit current acceptance (to high resistance (too low short circuit current) and the fuse/circuit breaker will not switch off in required time in case of short circuit)

author: Nusa
author_rank: Super Contributor
timestamp: October 20, 2021, 10:23:50 am
content: Quote from: Yaroooo on October 20, 2021, 09:23:24 amYou'd probably have better luck educating yourself if you found example datasheets in a native language you can read. Don't expect the provided english translations of Chinese to make sense. The 70A is for instantaneous current, which is not the same thing as the 32A rated current. Google that if you want to try understanding that, but rated current is the number you use as a don't-exceed value. The voltage rating of an insulated wire is the rating of the insulation, the wire itself doesn't care about voltage. Length is not directly mentioned because it's not long enough to be a significant factor, unless you're stringing long wires between buildings. For instance, a 10 awg solid copper wire should ballpark around 1 ohm of resistance per 1000 feet at a nominal temperature. You can find charts for this stuff if you're in the lineman business.

author: David Hess
author_rank: Super Contributor
timestamp: October 20, 2021, 09:17:52 pm
content: The voltage does not affect loss, only the current and resistance does.There is a separate table for the wire size required for a given current and distance which depends on the maximum allowed voltage drop. Longer cables require larger wire size because otherwise the voltage drop becomes too great.

author: TimFox
author_rank: Super Contributor
timestamp: October 20, 2021, 09:53:14 pm
content: Currentsafetyratings for wire diameters are a function of allowable temperature rise. As the wire length increases, at a given current value, the power dissipation increases linearly with the length, but the thermal conduction away from the metal increases approximately linearly. These ratings depend on installation (in cable, in conduit, free air, transformer winding, etc.), but the safety rating ordinarily does not guarantee voltage drop, which must be calculated separately.

author: wizard69
author_rank: Super Contributor
timestamp: October 25, 2021, 09:11:38 pm
content: Quote from: TimFox on October 20, 2021, 09:53:14 pmTim has this right. If the cable is going into a regulated environment, for example installations covered by the NEC (National Electric Code), you need to follow those regulations. I'm a bit rusty with code so I will avoid specifics but common wire sizes, like 14 and 12 AWG have current limits set by the NEC. Other sizes require that you take into account a large number of factors to arrive at the current carrying capacity.In short if you have a covered installation you need to make sure you are compliant with the latest NEC requirements.

author: Jwillis
author_rank: Super Contributor
timestamp: October 27, 2021, 06:47:28 pm
content: Quote from: Yaroooo on October 20, 2021, 09:09:49 amCopper wire can handle much higher currents than it's AWG rating . For instance with the 10 AWG wire 15A rating is actually only 4.5% of its fusible (Wire melting current) rating . 10 AWG copper will fuse (melt) at 333A .As for the amount of power dissipated by the wire you can calculate it as P (power dissipated) = I2(current) × R (resistance)Since 10AWG wire has a resistance of 0.9989/ 1000ft(304m) @ 20oC . 1m of 10AWG wire would dissipate about .003W . Which is insignificant for 10 AWG wire .For electronics your main concern is voltage drop over long distances . So you would select your wire based mainly on it's resistance over a specified distance .The thicker (lower the Gauge ) the less resistance it will have over a specified distance . Of course current carrying capacity is important as well , but as the example shows you have plenty of leeway .Generally you don't want more than 10oC increase over ambient but a little more shouldn't be problem .The NEC is not used as a reference for electronics or automotive . The AWG current rating is for chassis wiring only and not civil structural wiring . So don't get the two confused . Never use the AWG current rating when referencing the NEC for house wiring.The NEC recommended voltage drop of a feeder plus a branch is 5% and 1% for sensitive equipment . These are recommendations only .

author: TimFox
author_rank: Super Contributor
timestamp: October 27, 2021, 06:59:38 pm
content: Your idiosyncratic punctuation (space in front of period) makes your calculation hard to understand.Are you calculating the power dissipation in 1.0 m of AWG 10 at 15 A, or in 0.1 m (4 in), or at some other current?1.0 m of AWG 10 (0.0033 ohms) would dissipate 0.74 W at 15 A and 0.1 m would dissipate 0.074 W.The NEC (National Electrical Code) for civil structural wiring is a fire-prevention code (from the NFPA).AWG (American Wire Gauge) is a wire gauge, defining the diameter of the wire, used for copper wire.The reference in a copper wire table states, as a footnote to the 55 A current rating for AWG 10,"Maximum current for chassis wiring. Data from Handbook of Electronic Tables and Formulas for American Wire Gauge. The maximum current for power transmission is less."

author: Trader
author_rank: Frequent Contributor
timestamp: October 27, 2021, 07:37:26 pm
content: Quote from: Yaroooo on October 20, 2021, 09:23:24 amI have this connector, avoid it, that middle part isn't fixed and have a very bad contact.

author: Jwillis
author_rank: Super Contributor
timestamp: October 27, 2021, 10:41:56 pm
content: Quote from: TimFox on October 27, 2021, 06:59:38 pmOh sorry Tim . Your right my math is way out to lunch . Not feeling well at all today . Should have passed on the thread completely. Damage done.Anyway I wanted to convey that the off the net AWG current ratings are not the same as the NEC current ratings for same gauge wire , The 15A rating is for bundled wires and the chassis rating is for single wire . But the Ampacities of Insulated Conductors From NEC Table 310.16 (2020 edition) for 10 AWG wire are 30A for 65oC , 35A for 75oC and 40A for 95oC with certain recommendations as stated in the notes.Notes:1. Section 310.15(B) shall be referenced for ampacity correction factors where the ambient temperature is other than 30 C (86 F).2. Section 310.15(C)(1) shall be referenced for more than three current-carrying conductors.3. Section 310.16 shall be referenced for conditions of use.*Section 240.4(D) shall be referenced for conductor over current protection limitations, except as modified elsewhere in the Code.But its best for people to refer the actual Code which entails much more than the current capabilities .Just wanted to reassure that wire won't suddenly burst into flame and melt if the AWG current rating is exceeded by a small margin.I apologize for the confusion.