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Wire Gauges

Old 08-29-2016, 11:08 PM
  #1  
Suprawill1
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Default Wire Gauges

It appears to me that the largest wires in my set-up are 10awg and the smallest may be 14awg. The larger coming from the 6S lipo and leading into the 100A ESC. The smaller leading from the motor of the RC Lander 70mm EDF.
I have an electrical friend that is wondering how the heck 80A is being pulled through these size wires. Is he or I missing something?
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Old 08-29-2016, 11:51 PM
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dereckbc
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Not really a question of what he is missing, rather a different set of standards or lack of them. .

I assume he is like me from the world of NEC aka National Electrical Code from NFPA. Electrical codes for buildings, structures, homes, ect... 100 Amps in his world requires a minimum 2 AWG copper. About the size of your index finger in diameter. Cable Insulation used in building Power and Lighting Cable has a Temp rating of 75 to 90 C. In addition the NEC is very Conservative with Cable Current Capacity. They have to be, otherwise thousands would die via electrical fires. That is how and why they are put in place.

Model Airplanes do not have any Industry Electrical Codes that I am aware of. They use cable Insulation Types with higher Temp ratings like MTW rated for 140 C. That means they can run cables hotter, and since distances or so short voltage and power losses are acceptable limits. Basically taking the wire to the edge of the thermal limits and playing with fire.

Anyway Electrical codes vary among the Industry. Buildings use NEC which is what your friend uses. Autos use SAE. and Marine ABYC. RC Models unknown, and that is throwing your buddy because wire sizes vs maximum current ratings to a Standard he knows. To him 10 AWG is only good for 35 amps under certain conditions, otherwise 30 amps. 100 amps on !00 AWG is Nucking Futs to him. Last thing he wants is a 300 F degree conductor in his walls.
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Old 08-29-2016, 11:52 PM
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I'm sure voltage plays a factor. You're running 25v versus say 110/115v or 220v.

EDIT - Dereck posted just before me. I like his response better.
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Old 08-30-2016, 02:53 AM
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Originally Posted by dereckbc View Post
Not really a question of what he is missing, rather a different set of standards or lack of them. .

I assume he is like me from the world of NEC aka National Electrical Code from NFPA. Electrical codes for buildings, structures, homes, ect... 100 Amps in his world requires a minimum 2 AWG copper. About the size of your index finger in diameter. Cable Insulation used in building Power and Lighting Cable has a Temp rating of 75 to 90 C. In addition the NEC is very Conservative with Cable Current Capacity. They have to be, otherwise thousands would die via electrical fires. That is how and why they are put in place.

Model Airplanes do not have any Industry Electrical Codes that I am aware of. They use cable Insulation Types with higher Temp ratings like MTW rated for 140 C. That means they can run cables hotter, and since distances or so short voltage and power losses are acceptable limits. Basically taking the wire to the edge of the thermal limits and playing with fire.

Anyway Electrical codes vary among the Industry. Buildings use NEC which is what your friend uses. Autos use SAE. and Marine ABYC. RC Models unknown, and that is throwing your buddy because wire sizes vs maximum current ratings to a Standard he knows. To him 10 AWG is only good for 35 amps under certain conditions, otherwise 30 amps. 100 amps on !00 AWG is Nucking Futs to him. Last thing he wants is a 300 F degree conductor in his walls.
The answer I was looking for! Thanks!
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Old 08-30-2016, 02:55 AM
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Originally Posted by crxmanpat View Post
I'm sure voltage plays a factor. You're running 25v versus say 110/115v or 220v.

EDIT - Dereck posted just before me. I like his response better.
That's what I originally thought but according to him, voltage plays no part. Only current determines cable thickness or resistance.
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Old 08-30-2016, 03:21 AM
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Originally Posted by Suprawill1 View Post
That's what I originally thought but according to him, voltage plays no part. Only current determines cable thickness or resistance.
Voltage plays some part, but that has to do with how THICK the Insulation is vs Operating Voltage. Low voltage cables are rated 300 volts with thin inulsation, where as building power conductors are 600 volts and higher with thicker insulation. If you were to look at say Medium Voltage cable like 4160 volts, the insulation is very thick.

But when it comes to Current, it is circular mills of the conductor (diameter or cross sectional area), and Cable Insulation Temp rating.

Building Power and Lighting wire and cable insulation has lower Temperature ratings of 60, 75 and 90 Celsius. However when it comes to machinery, automotive, and marine use much higher Temperature Insulation of 140 to 190 Celsius, thus it can take more current or heat.

Keep in mind Power is the product of Voltage and Current, Power = Voltage x Current. So lets say I have 2 x 1000 watt motors. One operates @ 10 volts and one at 100 volts. The 10 volt motors requires 100 amps and some very large conductors. The 100 volt motor only takes 10 amps and much smaller wire. Both can use the exact same cable insulation of 300 volts.
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Old 08-30-2016, 03:32 AM
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Originally Posted by dereckbc View Post
Voltage plays some part, but that has to do with how THICK the Insulation is vs Operating Voltage. Low voltage cables are rated 300 volts with thin inulsation, where as building power conductors are 600 volts and higher with thicker insulation. If you were to look at say Medium Voltage cable like 4160 volts, the insulation is very thick.
Yes, my friend did mention this. You need thicker insulation for higher voltage to prevent arc-ing.
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Old 08-30-2016, 05:22 AM
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You can look up ampacity charts for wire.

I thought the same thing when I first started, but it turns out our wire is OK , but sometimes I see stuff that makes me wonder how hot our wire can get during heavy use.

Connectors can be the weak link in an electrical system, I have had Deans type connectors melt down, that is why I have switched to XT60's, not one problem since.
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Old 08-30-2016, 06:19 AM
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Originally Posted by Wildflyer View Post
You can look up ampacity charts for wire.

I thought the same thing when I first started, but it turns out our wire is OK , but sometimes I see stuff that makes me wonder how hot our wire can get during heavy use.

Connectors can be the weak link in an electrical system, I have had Deans type connectors melt down, that is why I have switched to XT60's, not one problem since.
I'm glad you mentioned that Wildflyer because I was just told that Deans are suspect and even in their good state, they only hold 65A.
I had already ordered and received my new lipo with a Deans connector and also ordered a Deans pigtail to mate it with. I now have to cut these off and reattach with something else.
I have a system that will draw 80A and have a 100A ESC to counter with so it had been mentioned that I should get the XT90s because the 60s also max at 65A. My other choice, which I am inclined to go with, is the bullet style and I think I'm going with the 5.5mm size. Those are rated at 150A.
My only question is, I'm going with the solder on style and I'm wondering if heat shrink will be sufficient insulation for 26 volts. Any thoughts?
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Old 08-30-2016, 09:41 AM
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Great post. I'm flowing similar currents in my 6S edf's. I have one that has a mix of wire sizes with the smaller size having the greatest length from the esc to the deans connector. Not good.

Was doing some brief taxi tests and noticed that the deans connector and wire from esc was quite warm. Changing it out. I agree the deans is okay to a point. Many of my 6s lipos come with EC5's. I've been using two way EC5 to Deans adaptor plugs. Rethinking.
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Old 08-30-2016, 03:20 PM
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For connectors, anything that runs 4S or lower I use T-connectors (the Hobby King Deans knockoffs). Anything over that gets EC5s.
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Old 08-30-2016, 04:05 PM
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Originally Posted by Suprawill1 View Post
My only question is, I'm going with the solder on style and I'm wondering if heat shrink will be sufficient insulation for 26 volts. Any thoughts?
More than enough,
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Old 08-30-2016, 05:58 PM
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Don't forget that 120/240 wiring may be inside conduit with no air circulation. Moving air makes a Huge difference in temperature rise of copper wire.

A while back, I ran a temperature rise test on #12 wire at a constant 90 Amps. The temperature leveled of at 180 F. With no air circulation.

Last edited by kyleservicetech; 08-30-2016 at 07:43 PM.
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Old 08-30-2016, 07:04 PM
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Originally Posted by kyleservicetech View Post
Don't forget that 120/240 wiring may be inside conduit with no air circulation. Moving air makes a Hugh difference in temperature rise of copper wire.

A while back, I ran a temperature rise test on #12 wire at a constant 90 Amps. The temperature leveled of at 180 F. With no air circulation.
Good observation.
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Old 08-30-2016, 07:47 PM
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Forgot to mention on that temperature rise test at 90 Amps. My APP connector terminals also hit the same 180 F.

The Deans connector at the same current melted the solder on the connector. Obviously that's way over the current rating of the Deans units.

I'm running 130 Amps through my Castle Creations 6.5 mm connectors. They don't even get warm.
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Old 08-30-2016, 08:08 PM
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Also interested in those EC5 connectors. Just like any other types, there are knock offs of these too. What is the brand name of the genuine EC5s?
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Old 08-30-2016, 08:37 PM
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EC connectors are an E-flite product. There are three sizes; EC2, EC3, and EC5.
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Old 08-30-2016, 08:42 PM
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Thanks Turner!
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Old 08-30-2016, 08:44 PM
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dereckbc
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Originally Posted by kyleservicetech View Post
They don't even get warm.
No connection should ever be warm. Otherwise there is a problem.
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Old 08-30-2016, 09:06 PM
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Suprawill if your friend is shocked at the size of wire used in model flight, show him some EC3 Connectors and tell him they are good for 60 Amps. He should turn as white as a sheet. This is one area where the limits are beyond reasonable risk IMO.

Its all about contact surface area, A NEMA 5-15P found on every 120 volt device you have is rated for 15 amps, and it has more surface area and mass than any of the connectors.

A 60 Amp Plug / Receptacle for a NEC code compliant device would weigh as much as the plane.

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Old 08-30-2016, 09:22 PM
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Originally Posted by dereckbc View Post
Suprawill if your friend is shocked at the size of wire used in model flight, show him some EC3 Connectors and tell him they are good for 60 Amps. He should turn as white as a sheet. This is one area where the limits are beyond reasonable risk IMO.

Its all about contact surface area, A NEMA 5-15P found on every 120 volt device you have is rated for 15 amps, and it has more surface area and mass than any of the connectors.

A 60 Amp Plug / Receptacle for a NEC code compliant device would weigh as much as the plane.

I know, right? I believe your initial explanation has him headed in the right direction.
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Old 08-30-2016, 09:32 PM
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I am also looking for 3.5mm bullet motor extension wires, preferably 14awg. It seems that when I find this gauge, they only come in pairs instead of triplets. Don't all these EDF motors have 3 leads?
Most that have 3 wire extensions are 16-18awg. Isn't the motor pulling most of the current in these set-ups?
You've got 10 gauge coming from the battery and into the ESC, then my 100A ESC has what looks like 12 gauge going to the motor but the motor on this RC Lander EDF with 80A draw has 3.5mm bullet connectors with what looks like 14 gauge wires and all I can find for 3.5mm bullet extensions are 16-18 gauge?
Maybe I'm starting to sound like my NEC friend but can someone enlighten me?
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Old 08-31-2016, 12:05 AM
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Leads to the motor getting warm possibly but just how hot do the wires inside the motor get?
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Old 08-31-2016, 12:15 AM
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Originally Posted by quorneng View Post
Leads to the motor getting warm possibly but just how hot do the wires inside the motor get?
I would guess hot enough to not want to exacerbate that condition by starving it with under-gauged wires. (creating more heat)
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Old 08-31-2016, 12:51 AM
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Originally Posted by quorneng View Post
Leads to the motor getting warm possibly but just how hot do the wires inside the motor get?
That is difficult to measure. The usual method is to measure the motor winding resistance, both hot and cold. Standard formulas exist to calculate temperature rise.

That does call for a precision microohmmeter. Problem is, these small motors cool off very rapidly after power is reduced after landing.

One way to measure it would be to use a thermocouple type thermometer with the sensor stuck into the motor windings. Difficult to do when the model is in flight.

Somewhere I've got a photo of a Hacker A40-10L motor and a 3/4 HP 120 VAC motor. That 120 VAC motor outweighs the Hacker motor by perhaps 20 times. Both have the same horsepower.

But without that 50 MPH airflow, the Hacker might melt it's windings at constant full power.
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