No lawyer or expert here.....but....right in the CFRs (legal vs ABYC standard)
"The use of twist-on type
wire nuts is permitted under the following conditions:"
46 CFR 183.340 and 46 CFR 111.60-17
§ 111.60-17 Connections and terminations.
(a) In general, connections and terminations to all conductors must retain the original electrical, mechanical, flame-retarding, and, where necessary, fire-resisting properties of the cable. All connecting devices must be suitable for copper stranded conductors.
(b) If twist-on type of connectors are used, the connections must be made within an enclosure and the insulated cap of the connector must be secured to prevent loosening due to vibration.
(c) Twist-on type of connectors may not be used for making joints in cables, facilitating a conductor splice, or extending the
length of a circuit.