Snap Action Breaker Values for the Motors?

[ChuckDickerson]

IIRC there has always been a section in the manual that lists what values (20A, 30A, 40A) must be used with certain motors. The CIMs and FP we could run at 40A, the others were either 20A or 30A. I have read the relevant sections of the manual a couple of times now and don't find these values defined. Am I just missing it? Can someone point me to these rules?

[Kevin Sevcik]

You don't see them because they aren't there. I can't actually recall the last year there was such a rule. Prior to 2006 at least.

At any rate, fusing/breaker protection is primarily to protect the wire, since it can melt, catch fire, etc. So the manual actually lists what size wire you must use for a circuit off a particular breaker. Or vice versa. Protecting the motor is on your own look out. If you want to power a globe motor off a jaguar with a 40A breaker, you're welcome to. It's somewhat foolish and likely to fry the motor if it stalls, but it won't catch fire, so it isn't FIRST's concern.

[Al Skierkiewicz]

Kevin,
The Globe will catch fire under those circumstances as the varnish melts off the wire in the armature and the short wires feeding the motor go incandesent. As in past years,
<R46> All active Power Distribution Board branch circuits shall be protected from overload with an appropriate value auto resetting Snap Action circuit breaker (from the Kit Of Parts or identical equivalent).
A. Each speed controller branch circuit must be protected by one and only one 20-amp, 30-amp, or 40-amp circuit breaker on the Power Distribution Board. No other electrical load can be connected to the breaker supplying this circuit.

This rule allows teams to use their discretion on electrical design. I have seen teams use 20amp breakers on CIM motors. However the limiting factor is knowing what the stall current on a motor is and designing your system accordingly. Although the stall current on a CIM motor is 129 amps, it rarely should draw that much. Combined with the operating spec of the breaker, 40amp breakers are appropriate in that application. Please review R54 as well so that motor loads are not connected to devices that will be damaged if used together.

[MrForbes]

Al, do the lead wires that are part of the CIM and Globe motors need to be protected by an appropriate sized breaker?

[Al Skierkiewicz]

There is nothing in the rules that concern these motors directly. The leads on the CIM motors are #12 and are short enough that I recommend (and Wildstang employs) mounting the speed controllers close to the motors and then use only the motor leads to connect to the controller. In this way a second set of connections is eliminated and thus a second point of failure. The Globe motors have a much smaller guage, #18 or #20 as I remember.