Hubbell ground fault and circuit tester with straight blade. This unit is designed to measure the trip level of GFCI portables, receptacles, or breakers within any range from 2 to 7 mill amperes, or the leakage in portable tools or appliances within a leakage range of 1 to 7 mill amperes It can be used on any AC circuit of 110 to 130V. While conventional 3 wire grounding is essential to electrical safety on board any boat, it cannot protect against minute line-to-ground faults that cannot activate protective devices such as fuses or circuit breakers. Conventional overcurrent protection.