PPE is required for voltage testing, i.e., "00" or "0" voltage rated gloves with leather protectors, plus voltage rated test equipment. This also means the proper category. CAT I, II, III, IV. The closer to the utility source the higher the category instrument required for safe testing.
See NFPA 70E Table 130.7(9)(a) for Panel Board Rated at 240V and Below for PPE required.