Quote:
Originally posted by Mike Betts
CBP:
The amount of current a wire can take is a function of the diameter (AWG) and the type/thickness of insulation. The type of insulation determines the temperature at which the wire will fail. The thickness (among other factors) determines the voltage at which the wire will suffer a dielectric breakdown and arc over.
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Thanks Mike,
the type of insulation affects the current capability as interpreted by the electrical safety councils and the National Electrical Code (which in turn is driven by the insurance companies) and is mostly determined by it's melting point or the point at which the temperature of the wire is sufficient to melt the insulation and contact another conductor. The safety devices (breakers) must therefore open the circuit before the wire reaches that temperature based on known current heating, wire size and whether the conductors are in conduit or in free air. Since all wiring to motors on our robots are protected by 30 amp circuit delayed action circuit breakers, it follows that wiring should be capable of all characteristics of that type of protection. Using #16 wire to feed a Globe seems like an OK thing to do unless you consider that a moving part, pinching the wires might cause a short in the wire. It is conceivable that a #16 wire would set itself on fire before the breaker would open. Hence the rule.
Now many of you are going to bring up that the drill motor has #16 wires supplied and it has 129 amps at stall. Well, check the small printing on the wire and you will see that the insulation has a melting point of 105 C.
Many teams are reporting heating of the drill motors. As pointed out in these forums on many occasions and in the Robot docs, the drill motors are not designed to get rid of heat at low RPM. If you design your drive system such that maximum current is drawn at low RPM or near stall, the wire and the motor will reach temperatures at which the wiring, the brush assy, the soldered connections and/or the motor will fail. You must get the operating RPM on the motor into a more efficient range.