John Gill Commentary 1 Chronicles 4:15

"And the sons of Caleb the son of Jephunneh: Iru, Elah, and Naam; and the sons of Elah; and Kenaz." — 1 Chronicles 4:15 (ASV)

And the sons of Caleb the son of Jephunneh
Jephunneh is not the same with Hezron, as the Targum, but another son of Kenaz, hence called the Kenezite, (Joshua 14:6) and brother of Othniel; and Caleb his son is the same that was sent one of the spies of the land of Canaan by Moses, see (Numbers 13:6) (14:6)

his sons were Iru, Elah, and Naam ;
of whom we nowhere else read:

and the sons of Elah, even Kenaz ;
another Kenaz, or rather it should be read Uknaz; so Jarchi and Kimchi.