[InFlight]

You may be able to find 40 amp slip rings, but all the ones I've seen are large and very expensive.

Both the M1330 and the MW1440 (4 wires, 30 amp per contact) both use 12 gage wire. Thus the wire size meets the R38 requirement for 40 amps.

R 37 states that you may use up to a 40 amp breaker for motor controllers, thus a 30 amp breaker to match the contacts is thus also permitted and fully compliant.

For a 40 amp rating; It seems like it could be permissible (R39) to splice two contacts in parallel (w/ MW1440) to achieve the 40+ amp load rating. Would be a good area for a rule interpretation, as it would make slip rings a more available and useable device.

[U]R39 Branch circuits 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/rated elements.[/u]

Probably enough hijacking of this Swerve Drive thread on encoders and slip rings.