46 CFR §111.60-17

1. (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.
2. (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.
3. (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.