I've never needed more than 3.5A for heater supply. Now that I need some more, I'm thinking more carefully about wire gauge.
I have some stranded 0.5mm^2, consisting on 16 strands of 0.02mm diameter.
Now, AWG20 is something close to 0.5mm^2.
It is usually recommended for 7 A maximum.
According to this:
Wire and Cable Ampacity Ratings | Anixter
(More current-carrying conductors in an enclosed space may result in a greater ambient temperature. The ampacity of those conductors must be derated to account for this increase in ambient heat.)
Should I derate to 45% the current capacity of the wire?
To about 3A?
This is not something to take into account the space between individual conductors, because the wire I'm talking about consists of 16 strands of 0.2mm diameter wire, which is 0.031mm^2, and 16 x 0.031 is 0.5mm^2. Same area. Same current capacity. In theory.
I'm sure many people here have wired amps with heavy filament currents (>7A). Is this wire safe for 7A ? It is silicone rubber insulated.
I have some stranded 0.5mm^2, consisting on 16 strands of 0.02mm diameter.
Now, AWG20 is something close to 0.5mm^2.
It is usually recommended for 7 A maximum.
According to this:
Wire and Cable Ampacity Ratings | Anixter
(More current-carrying conductors in an enclosed space may result in a greater ambient temperature. The ampacity of those conductors must be derated to account for this increase in ambient heat.)
Should I derate to 45% the current capacity of the wire?
To about 3A?
This is not something to take into account the space between individual conductors, because the wire I'm talking about consists of 16 strands of 0.2mm diameter wire, which is 0.031mm^2, and 16 x 0.031 is 0.5mm^2. Same area. Same current capacity. In theory.
I'm sure many people here have wired amps with heavy filament currents (>7A). Is this wire safe for 7A ? It is silicone rubber insulated.
Ampacity is concerning heating of wires only. Derating is done when ambient Temp exceeds some test limits, sheathing vs open air etc. IMO this is stuff for the electricians and fire marshals. That being said, silicone insulation is rated much higher temperature than normal insulation materials, so the copper content could be be much less on wiring sold by ampacity #'s.
I would be concerned with the voltage drop per unit length and verifying the actual amount of copper or AWG of muti-strand sillycone wire from any anonymous sources. FWIW Ive seen some discrepancies of claimed AWG here from china export products or others sold outside of the regular industrial distribution channels.
Id calculate max currents allowing for less than 2.5% V drop @ last filament run. Less drop is better right? 20AWG seems awfully light, but is probably OK for short runs. It might be prudent to de-rate hobby wire by a couple of gauges unless you measure it.
I would be concerned with the voltage drop per unit length and verifying the actual amount of copper or AWG of muti-strand sillycone wire from any anonymous sources. FWIW Ive seen some discrepancies of claimed AWG here from china export products or others sold outside of the regular industrial distribution channels.
Id calculate max currents allowing for less than 2.5% V drop @ last filament run. Less drop is better right? 20AWG seems awfully light, but is probably OK for short runs. It might be prudent to de-rate hobby wire by a couple of gauges unless you measure it.
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FWIW I run almost 8A through 22 solid. No issue, no heating. About a 12 inch run. The longer the run the thicker the wire.
Try and find the original manufacturer datasheet for the cable your have, or see if there are any markings on the insulation sheath - if so then google for a datasheet of an equivalent cable. The datasheet should have current carrying capacity for the cable. If you are under that rating then the temperature of the copper wire won't exceed the capability of the insulation for long term use.
Even for short wires, the gauge is important, because the heat dissipation is per unit length.
Most wires (datasheets) I've seen from big online electronics supplies stores don't talk about the current capacity. Voltage rating, insulation type, temperature,... but not amperage.
I think the best way to know for sure is to test them and measure the temperature rise.
Most wires (datasheets) I've seen from big online electronics supplies stores don't talk about the current capacity. Voltage rating, insulation type, temperature,... but not amperage.
I think the best way to know for sure is to test them and measure the temperature rise.
Aren't you overthinking this, just for a fun experiment how do you propose to measure this temp?
Ampacity ratings are used to make sure the electrical breakers or fuses can properly shut down on faults / overloads and not slowly cook off wires insulation into a smoldering flame.
Therefore it's not useful for steady state operation of filaments. Your tubes wont be working if your silicone wires are running @100*C rise
.
Just calculate the resistance of the copper from data sheet or ( OR measure 1 meter ) and figure the voltage drop based on your current of 7A RMS. Si Senor?
.
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super easy way to measure a wires resistance.
1)Using an ordinary lab power supply , set the current limit on the PS to 1.00A by shorting across the terminals with a fairly accurate DMM set on Amps.
2) now insert 1 meter of wire to be tested and measure the voltage drop at the ends.
using R = V/ I where I = 1 you can simply read resistance directly on the millivolt range. V = ohms /M
1)Using an ordinary lab power supply , set the current limit on the PS to 1.00A by shorting across the terminals with a fairly accurate DMM set on Amps.
2) now insert 1 meter of wire to be tested and measure the voltage drop at the ends.
using R = V/ I where I = 1 you can simply read resistance directly on the millivolt range. V = ohms /M
Well, using a constant current source (like powering the filaments of a set of tubes) and using the temperature probe of my DMM, which is fairly accurate, on a insulation stripped portion of the wire. Once the temperature raises above, let's say, 70ºC, I'd stop increasing current. Never tried. Just a quick idea.
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