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A milliohm meter is a four-wire instrument, and it only works as one. You pass a known current through the unknown resistance on one pair of leads and measure the voltage across it on a second pair, so the lead and contact resistance drops out of the result. Connect the Kelvin clips so that the current and sense contacts touch the conductor at separate points, short the clips together and zero the display before you measure, and keep the meter within its published range. The AideTek VC480C and the Extech 380560 are both four-wire instruments with Kelvin clips and a zero adjustment, which is the minimum equipment for the job. A clamp meter such as the ZIBOO 393 and a solar panel tester such as the LODESTAR LD673PV measure current and voltage, not low resistance, and cannot substitute for a milliohm meter.
Why two wires are not enough below one ohm
Every test lead is a resistor. A metre of ordinary meter lead is perhaps a few milliohms, and the contact between the probe tip and the terminal adds more. When you measure a 10 kΩ resistor with a two-wire multimeter, a few milliohms of lead resistance changes the answer by less than one part in a million, so nobody cares. When you measure a 5 mΩ busbar joint, the same few milliohms is the same order of magnitude as the thing you are trying to measure. The meter cannot tell the difference between the joint and its own leads.
The four-wire, or Kelvin, connection solves this by separating the jobs. One pair of leads carries a known test current through the unknown resistance. A second pair measures the voltage across it. The voltmeter side draws almost no current, so the voltage drop in those leads is negligible, and the current leads are outside the voltage measurement. The meter calculates resistance from the current it forced and the voltage it saw at the sense terminals. Lead resistance cancels.
This is why the Kelvin clip exists. It is a single clip with two contacts that are insulated from each other, one carrying current and one sensing voltage, arranged so both touch the conductor at very nearly the same point. You do not have to hold two probes on a small terminal. The listing for the AideTek VC480C describes four-wire cables with Kelvin clip connectors, and the Extech 380560 lists gold-plated Kelvin clip leads. That construction is the defining feature of the instrument class, not an accessory.
Setting up: short, zero, then measure
The sequence matters more than the meter model. Clip the two Kelvin clips firmly to each other, metal to metal, with no insulating film between them. That gives the meter a known near-zero resistance. Press the zero or relative button and the display should read zero. This step removes the residual offset of the clip contacts and any thermal EMF in the leads. If the meter will not zero, the clip faces are dirty or the leads are damaged.
Then connect the clips to the conductor under test. Both clip jaws must close on clean metal. Paint, oxide, solder mask and loose corrosion are insulators at these resistance levels, and a reading taken through them is a reading of the contamination, not the joint. Where the listing provides a zero adjustment, as the AideTek listing does, use it every time you change leads or range. The Extech listing describes a data hold function; hold is for recording a settled reading, not for capturing a drifting one.
Watch the range. The Extech 380560 listing gives three ranges, 200 mΩ, 2000 mΩ and 20 Ω, with 0.1 mΩ resolution. Resolution is the smallest display step, not the accuracy. A display that moves in 0.1 mΩ increments can still be wrong by more than that, and no listing here publishes an accuracy figure for the milliohm function. Treat the last digit as an indicator, not a certificate.
What the reading can and cannot tell you
A milliohm meter tells you the resistance between its clip contacts at the moment of measurement. That is all. It does not tell you the temperature of the conductor, and copper resistance rises with temperature, so a joint measured warm reads higher than the same joint cold. It does not tell you whether the joint will stay at that resistance under load, which is the failure mode that matters in switchgear and battery connections. Contact resistance often rises only when current flows and the contact heats.
For a comparison to mean anything, measure the same joint in the same way at the same temperature, and compare it with an identical joint nearby rather than with an absolute number. A busbar joint reading a little above its neighbours is a candidate for inspection. A joint reading the same as its neighbours is probably fine, whatever the absolute figure. This is a trend instrument as much as a pass or fail instrument.
The listing for the AideTek VC480C states that it is intended for conductors, electric heating elements and solder points. That is the correct territory: low-resistance paths where a fraction of an ohm matters. It is not a general multimeter and it will not measure a resistor decade box or a sensor.
The mistakes that produce a confident wrong number
The most common error is using the meter in two-wire mode, or clipping both Kelvin contacts to the same side of a terminal so that the current and sense paths share a contact. Either mistake reintroduces the lead and contact resistance the instrument was built to remove. The reading will be stable, plausible and wrong. The second most common is failing to zero after changing range or leads. The third is measuring through an insulating layer: a clip on an anodised aluminium busbar or on a painted steel chassis reads open or wildly high because the contact is not metal to metal.
A fourth error is expecting the instrument to find intermittent faults. A milliohm meter is a steady-state instrument. A joint that only fails under vibration or thermal cycling will read normally when the meter is connected. Finding that fault needs a load test or a thermal camera, not a milliohm meter.
Finally, respect the test current. Four-wire meters inject a small current, but on a live circuit any injected current is a hazard and any circuit voltage is a measurement error. Isolate and prove dead before connecting. The listings here do not publish a CAT safety rating, so the safe assumption is that these are bench and de-energised-circuit instruments.
Where the milliohm meter stops being the right instrument
A milliohm meter is the wrong tool for anything that is not a low-resistance conductive path. It will not measure insulation resistance, which needs a high voltage and a completely different instrument. It will not measure earth electrode resistance, which needs a dedicated earth tester with a defined test current pattern. It will not measure the current a circuit is actually carrying, which is the job of a clamp meter such as the ZIBOO 393, and it will not characterise a solar panel, which is what the LODESTAR LD673PV is for.
If your question is whether a joint is good enough, a milliohm meter answers it only by comparison with a known-good joint. If your question is whether a circuit is live, or how much current it draws, or whether an insulation barrier holds, the milliohm meter is silent. Choosing the right instrument for the question is the same discipline described in choosing an environmental meter: match the sensor to the physical quantity, not to the display you find familiar.
For work that involves moisture and corrosion in buildings, the relevant instruments are different again, as set out in using a moisture meter on wood and on drywall. A damp joint corrodes, and corrosion raises contact resistance, but the moisture meter measures the moisture and the milliohm meter measures the consequence.
A short comparison of the instruments named here
The table below sets out only what the supplied listings state. Where a listing is silent, the cell says so rather than guessing.
| Instrument | Function | Connection | Stated ranges | Stated resolution | Zero adjustment |
|---|---|---|---|---|---|
| AideTek VC480C | Precision milliohm meter | 4-wire Kelvin clips | Not stated in the listing bullets | Not stated in the listing bullets | Yes, manual zero |
| Extech 380560 | Precision milliohm meter | 4-wire gold-plated Kelvin clips | 200 mΩ, 2000 mΩ, 20 Ω | 0.1 mΩ | Not stated in the listing bullets |
| ZIBOO 393 | Clamp meter, AC/DC current and voltage | Clamp jaw | Current to 1000 A; voltage to 1500 V DC | Not stated in the listing bullets | REL function for DC current |
| LODESTAR LD673PV | Solar panel tester | Panel leads | Voc 12 to 80 V; Isc to 35 A; to 1000 W | Not stated in the listing bullets | Not stated in the listing bullets |
Only the AideTek VC480C and the Extech 4-Wire are milliohm meters. The ZIBOO True RMS and the LODESTAR LD673PV are included because buyers often ask whether a clamp meter or a solar tester can do the job. They cannot: neither is a four-wire low-resistance instrument, and neither listing claims to be.
The method is the instrument
A milliohm meter is a four-wire measurement system, and the four-wire connection is what makes the number meaningful. Short the clips, zero the display, clip onto clean bare metal, and compare like with like at the same temperature. If the question is not about a low-resistance conductive path, put the milliohm meter down and pick up the instrument that measures the quantity you actually care about.
Frequently Asked Questions
Can I use an ordinary multimeter to measure milliohms?
Not reliably. A two-wire multimeter includes its lead and contact resistance in the reading, and that resistance is often larger than the value you are trying to measure. Some multimeters offer a relative or zero function that subtracts a shorted-lead reading, which helps, but it does not remove the contact resistance at the probe tips. A four-wire milliohm meter is the correct instrument.
Why do I have to zero the meter before every measurement?
Zeroing with the clips shorted together removes the residual resistance of the clip contacts and any small offset in the meter. It takes a few seconds and it is the difference between a reading you can compare with another reading and a number that drifts with lead condition. Zero again after changing range or leads.
What accuracy do the AideTek VC480C and Extech 380560 have?
Not stated in the listing bullets. The Extech listing publishes 0.1 mΩ resolution and three ranges, but resolution is not accuracy. Neither listing publishes an accuracy figure for the milliohm function, so no accuracy claim can be made here. Treat the last digit as an indicator and compare readings against a known-good joint.
Can a clamp meter measure low resistance?
No. A clamp meter measures current by the magnetic field around a conductor, and the ZIBOO 393 listing describes current and voltage functions, not four-wire resistance. It is the right tool for load current, inrush and voltage, and the wrong tool for a busbar joint.
Can I measure a solar panel with a milliohm meter?
No. A solar panel is characterised by its open-circuit voltage, short-circuit current and maximum power point, which is what the LODESTAR LD673PV listing describes. A milliohm meter injects a small current and measures resistance; it has no way to sweep a panel or report Pmax.
Is a milliohm meter safe on a live circuit?
The listings here do not publish a safety category rating, so the safe assumption is that these are de-energised-circuit instruments. Isolate the circuit, prove it dead, and only then connect the Kelvin clips. A milliohm meter is not an alarm and not a live-line tester.