Hioki FT6380-50 Clamp-On Earth Resistance Tester

Earth resistance by clamping the earth conductor, with a slim 20 mm jaw

The Hioki FT6380-50 is a clamp-on earth tester that measures the earth resistance of a multi-grounded system by clamping on the earth cable, with no auxiliary spikes to drive and no need to disconnect the earth. Hioki states clearly that it is for multi-grounded systems only. Its two cores perform voltage injection and current measurement: a defined voltage is injected into the loop, the resulting current is measured, and the loop resistance is calculated from the two.

The jaw is the practical feature. Hioki describes super slim jaws of 20 mm at the narrowest point, which can be opened with two fingers and clamped around cables in tight places, with a maximum measurable conductor diameter of 32 mm. There is no wait after switching on and no zero calibration. Magnetic shields between the two cores remove leakage flux that would otherwise affect accuracy, and the instrument weighs about 620 g without batteries.

The backlit LCD holds up to 2000 measurements in memory, and a HI/LO alarm sounds and shows when the resistance or current passes a set threshold. Hioki lists applications such as hazardous-area storage tanks and transmission towers. As the number of grounding poles in the loop grows, the measured value gets closer to the true value, so the method gives the best answer where many parallel earths exist.

Technical specifications

Where a clamp tester is the right tool

Clamp-on measurement suits earthing checks on pole grounding, towers, tanks and building installations where each earth electrode is connected to a common network. It cannot replace a fall-of-potential test on an isolated single electrode, because without a return path through other grounds no loop current flows. That limit is the main selection point, and engineers who need to test single rods or new installations normally pair a clamp tester with a spike-type earth tester.

The package contains the instrument, a carrying case, a resistance check loop (1 ohm +/-2 % and 25 ohm +/-1 %) for verifying the instrument in the field, a strap, two LR6 batteries and an instruction manual. The FT6380-90 is the same tester supplied with the Wireless Adapter Z3210, which sends readings by Bluetooth to the free GENNECT Cross app on a smartphone or tablet.

What to confirm before ordering

Confirm that the earthing arrangement is a multi-grounded system so that the clamp method applies, that the earth conductor fits within the 32 mm jaw, and whether wireless transfer is required (order the FT6380-90 or add the Z3210). Also state whether a calibration certificate is needed with the instrument.

Documents and quotation

The attached Hioki document is the FT6380-50 catalog in English. For a spike-type earth tester see the Megger DET4T2 four-terminal earth ground resistance tester, or browse the portable test and measurement category. Send the order code and quantity for a quotation from Seven Star LLC.