Under voltage protection is provided for bus-bars, rectifiers, transformers etc. IEC 61439 is a standard developed by the International Electrotechnical Commission (IEC) that covers design verification for low-voltage electrical products and assemblies. The IEC 61439. GE Multilin provides protective relays that support all busbar protection techniques, including overcurrent, high-impedance differential, and percentage (low-impedance) differential. The following points should be considered when selecting the correct busbars: REG terminal type (twin terminal or cage terminal), number of poles, device. Busbar protection (BBP): Protection intended to detect and operate to clear faults on a busbar.