Insulation resistance testers (megohmmeters) for electricians and maintenance techs: Klein ET600 vs Fluke 1507 vs Fluke 1587 FC and budget options, matched to test voltage (500V/1000V), motor, wiring and EV/appliance-service jobs, and to a multimeter that already covers the basics

welding equipment  · 

Pick the test voltage before the brand

An insulation resistance tester pushes a DC voltage through insulation and reads the leakage current as megohms. Pick the test voltage first, because it decides which meters qualify. Fluke’s insulation testing brochure pairs equipment rated up to 250 V with a 500 V test and a recommended minimum of 25 MΩ. It pairs 600 V and 1,000 V equipment with a 1,000 V test and a recommended minimum of 100 MΩ. In practice, 120/240 V branch wiring and small appliances sit in the 500 V group. 480 V motors and feeders usually call for 500 V or 1,000 V, depending on the equipment’s rating and your site’s procedure.

All three meters in this guide stop at 1,000 V DC. Medium-voltage cable, large generators and 5 kV equipment are tested at 2,500 V or more, which needs a different class of instrument. A fixed 500 V budget unit is fine for residential and light-commercial wiring. It leaves you short as soon as a job specifies 1,000 V.

Klein Tools ET600: fixed voltages and a simple layout

The Klein ET600 offers 125 V, 250 V, 500 V and 1,000 V test voltages and reads insulation up to 4,000 MΩ. Klein also lists AC/DC voltage measurement to 1,000 V, resistance and continuity, and a CAT IV 600 V / CAT III 1,000 V rating. Its warning alarm and high-voltage icon flag a live circuit before you test, which matters for the habit of verifying dead first.

That 4,000 MΩ ceiling covers most wiring and motor work, where a healthy reading in the hundreds or thousands of megohms is already a pass. The ET600 does not offer the timed polarization index and dielectric absorption routines that the Fluke 1507 and 1587 FC advertise. If you only need a single one-minute spot reading, that is not a loss. If you trend motors over years, plan on writing down timed readings by hand or choose a meter that calculates them.

Fluke 1507: the specialist’s range and ratios

The Fluke 1507 tests at 50 V, 100 V, 250 V, 500 V and 1,000 V and measures from 0.01 MΩ to 10 GΩ. That is a wider ceiling than the ET600 or the 1587 FC, so it can show how good very dry, clean insulation really is when other meters just read over-range. It calculates polarization index (PI) and dielectric absorption ratio (DAR) automatically, with a compare function for pass/fail checks.

Safety and convenience features include live-circuit lockout above 30 V, automatic discharge of capacitive voltage, 200 mA low-ohm continuity and a remote test probe for awkward terminations. The 1507 also reads AC/DC volts to 600 V and resistance to 20 kΩ, so it handles basic confirmation work. It is not a full multimeter, though, so you will probably still carry one.

Fluke 1587 FC: when one meter has to do both jobs

The Fluke 1587 FC is an insulation tester and a true-RMS multimeter in one body. Its insulation range is 0.01 MΩ to 2 GΩ at 50 V, 100 V, 250 V, 500 V and 1,000 V. Fluke’s datasheet lists Fluke Connect wireless logging, with Pi/DAR graphs, memory storage and temperature readings in the app. A technician who goes from a VFD fault to a motor winding check to a capacitor test in one visit gets the most from it.

The trade-off is range and cost. Its 2 GΩ ceiling is well below the 1507’s 10 GΩ, and an insulation multimeter is a bigger purchase than either dedicated insulation tester. The 1587 FC makes sense when it replaces a meter you would otherwise buy. If you already own a multimeter you trust, a dedicated tester usually gives better value for insulation work. Fluke also lists a 1577 in the same family, with 500 V and 1,000 V tests and a 0.1 MΩ to 600 MΩ range, for buyers who want the combined form at a lower tier.

Why an ordinary multimeter cannot stand in

A standard multimeter measures resistance with a few volts or less. Insulation breakdown often shows only under the stress of hundreds of volts, such as moisture tracking, pinholes or contamination in a winding. A multimeter ohms reading of “OL” across a motor lead and frame therefore does not show that the insulation will hold at operating voltage.

The 1,000 V DC source is also what lets you compare readings against the 25 MΩ and 100 MΩ minimums quoted above. A multimeter will tell you about continuity and voltage, and it should still be your first check to confirm the circuit is dead. The insulation test belongs to the dedicated tester or an insulation-capable meter such as the 1587 FC.

Matching the meter to motors, wiring and service work

For motors, test with the supply disconnected and locked out, from each winding to frame. A 500 V test suits 230 V motors, while 460 V and 480 V motors are commonly tested at 500 V or 1,000 V. If you plan to compare readings across years, take the PI (10-minute reading divided by the 1-minute reading) and DAR (60-second divided by 30-second); the 1507 and 1587 FC compute those for you. IEEE 43 treats a PI below about 2 as a concern for many insulation classes, so confirm the figure for your motor class.

For building wiring, disconnect electronic loads, surge protectors and dimmers first, because they can be damaged by the test or read falsely low. The same applies to drives, EV charging equipment and appliance control boards. For appliance heating elements and EV or hybrid high-voltage systems, follow the maker’s service manual for test voltage and acceptance limits. A general-purpose tester does not replace the procedure and rated protective equipment the manufacturer specifies.

Ownership, upkeep and the mistakes that produce bad readings

Leads, batteries and fuses are the usual ownership items. Check that the leads and probes carry a measurement category rating at least equal to the meter’s, and replace any with nicked insulation. The ET600 uses a replaceable battery and fuse, while the 1507 and 1587 FC each have their own battery and fuse specifications in the manual. Weak batteries can limit the test voltage the meter can hold, so a low-battery indicator should stop a test.

Most false results come from the setup. Surface moisture and dirt on terminals add leakage paths, so wipe and dry them before testing. Insulation resistance falls as temperature rises, and a common rule of thumb is that it roughly halves for each 10 °C rise, so log the temperature with the reading. Always let the meter discharge after a test: the capacitance of long cables or windings can hold a charge that is hazardous to the next person who touches the leads.

FAQ

Do I need a 500 V or 1,000 V insulation tester?

A 500 V test covers equipment rated to about 250 V, which includes most residential wiring and small appliances. Equipment rated 600 V to 1,000 V, such as many 480 V motors and feeders, is typically tested at 1,000 V. The Klein ET600, Fluke 1507 and Fluke 1587 FC all reach 1,000 V and also offer lower steps.

Is the Klein ET600 enough, or should I buy a Fluke 1507?

The ET600 handles spot checks at 125 V to 1,000 V and reads to 4,000 MΩ, which covers most wiring and motor checks. The 1507 reads to 10 GΩ and calculates PI and DAR, which suits technicians who trend motors or test very clean, dry insulation. If you only need a pass/fail reading, the ET600 is enough.

Can an insulation multimeter like the Fluke 1587 FC replace a separate multimeter?

Yes. The 1587 FC is a true-RMS multimeter with an insulation tester built in, so it can replace a second meter. The costs are a higher purchase price and a 2 GΩ insulation ceiling compared with the 1507’s 10 GΩ. If you already own a multimeter you trust, a dedicated tester is usually the better value.