Wire Gauge (AWG)

[zjbrannan]

I was wondering if anyone could help with determining what wire gauge I could use to wire my motors? Im using a CIM, a Fisher Price, a Banebot, and a window motor.

-Thanks!

[dez250]

[R44] Gives you a table that matches wire size to current / application. I would suggest you read over the whole section 4.1.7 of the Robot Rules to get familiar with other requirements too.

[thefro526]

Just Looked this up to order some wire.

[R44]
All active circuits shall be wired with appropriately sized wire:

Application
Minimum wire size
-40A circuit - 12 AWG (2.052mm)
-30A circuit - 14 AWG (1.628mm)
-20A circuit - 18 AWG (1.024mm)
between the PD Board and the Analog and/or Solenoid Breakouts if a common power feed is used - 18 AWG (1.024mm)

-between the PD Board and the Analog and/or Solenoid Breakouts if individual power feeds are used -20 AWG (0.8128mm)
-between the PD Board and the cRIO -20 AWG (0.8128mm)
-between the PD Board and the wireless bridge -20 AWG (0.8128mm)
-between the PD board and 5A custom circuits -20 AWG (0.8128mm)

-pneumatic valves - 24 AWG (0.5106mm)


The branch circuit may include intermediate elements such as COTS connectors, splices, COTS flexible/rolling/sliding contacts, and COTS slip rings, as long as the entire electrical pathway is via appropriately gauged conductors.

Wires that are originally attached to legal devices are part of the device and by default legal as supplied. Such wires are exempt from Rule [R44].

[Al Skierkiewicz]

Z,
The wire sizes and breaker ratings (as listed above) are matched to protect the wiring in the case of a fault. I generally recommend the use of #10 and 40 amp breakers when using the high current motors for drive systems. In the long run, the larger wire will maximize your motor performance.

[DonRotolo]

We generally go one size up (meaning #10 instead of #12) for all the recommendations, always for higher-current applications but sometimes for small stuff too.

#12 has a resistance of 0.00187 Ohms per foot. If I am using a total of six feet of it between the PDB and the motor (with a Jaguar in-between) - 3' of each color - I have 0.01122 Ohms.

We remember that V=I*R according to Ohm's Law.

If I am running 40 A to my motor, I am losing 40*0.01122 = 0.45 volts just from the wire.

Using #10 wire (0.00118 Ohms/foot) I lose .28 Volts, almost half.

[chi-town-biker]

Thanks for the advice Don. If I remember correctly the CIMs have 12 gauge wires. Just so I'm clear, you usually cut the CIM wires near the motor and solder on 10 gauge wire that you run back to the Jaguar? Or do you use a connector like a Powerpole to make the transition from 12 gauge to 10 gauge?

[Al Skierkiewicz]

chi,
It is far more simple to place the speed controller near enough to the motor that you can connect the motor wires directly to the speed controller. No splices are needed and the number of connections (failure points) are reduced.

[Bill_B]

I think the CIMs have 14 gauge leads. I sometimes wonder if the original designer of this motor knows about its extended life outside the initial specs.

[DonRotolo]

Originally Posted by chi-town-biker

Just so I'm clear, you usually cut the CIM wires near the motor and solder on 10 gauge wire that you run back to the Jaguar? Or do you use a connector like a Powerpole to make the transition from 12 gauge to 10 gauge?

If the wiring on the motor can reach the Jaguar, we just crimp on terminals. If the motor wiring doesn't reach the Jaguar - this is rare for us - we use Powerpoles with wires cut to maybe 8" (not too close, never know if you need to cut them again).

Also, the motor wires might be #14.

Wire is rated based on heat. If you put some #30 wire in liquid nitrogen, it'll happily run 20 A all day long. #14 wire in free, moving air will also handle 20 A happily enough. But since fire due to overheating wire is considered a catastrophe, conservatism is called for, and ratings are based on certain assumptions such as the wires not being in free air.

That's how CIM can put #14 wire on these motors: They know how they are likely to be used, and #14 is adequate.

[ratdude747]

the CIM wires are in fact 14 gauge. yes, that means they take "blue" crimp connectors, not "yellow" ones.

my only guess to why they only used 14 gauge for a 40A load is that it is such a short run that it "works".

[chi-town-biker]

Thanks everyone. That was helpful.

[zjbrannan]

Thanks for the help everyone!!