The Eaton Cutler-Hammer 21-Terminal Load Center Ground Bar is designed for use with Challenger, Eaton and Westinghouse load centers. Ground bars are required in all panels (main service panels include ground and neutral). To be sure you're selecting the correct ground bar, divide the number of circuits in the panel by 2 and pick the closest numbered ground bar. For example, a 20 circuit panel would require a GBK10P.