If you have circuit conductors spliced within a box or terminated on equipment within (or supported by) a box, any equipment grounding conductors (EGCs) associated with those conductors must be connected within (or to) the box [250.148]. Exception: the EGC permitted by Sec. 250.146(D) (for isolated ground receptacle applications) doesn’t have to be connected to the box or other ECGs.
Devices used to make those connections must be suitable for the use. And the connections must conform to Sec. 250.148(A) through (E):
(A) You can make connections with devices designed for brazing, welding, or soldering per Sec. 110.14(B).
(B) Arrange the grounding connections such that disconnecting a receptacle or other device doesn’t interrupt the grounding continuity. To conform to this requirement, pigtail to the device rather than use its grounding terminal to join incoming and outgoing EGC wiring.
(C) In metallic boxes, ensure an EGC connects to a dedicated grounding screw, equipment listed for grounding, or listed grounding device.
(D) In nonmetallic boxes, ensure an EGC can connect to a fitting or device requiring grounding.
(E) Don’t use any connection that relies solely on soldering.
