Micro-Ohmmeter and Ductor Testing Equipment for Hire

Megavar supplies micro-ohmmeters and ductor testers for hire across Australia, supporting contact resistance measurement on circuit breakers and switchgear, joint and connection resistance on busbars and conductors, and weld and bond integrity testing. The hire fleet covers the Megger DLRO low-resistance ohmmeter range across portable handheld units and high-current bench and field sets, from the everyday 10 A instrument through to high-current sets for the most demanding contact resistance work. The same instruments are used by Megavar commissioning engineers on substation and renewable energy projects every week.

A ductor test, the long-standing field name for a low-resistance measurement, answers one question that ordinary multimeters cannot: what is the true resistance of a current-carrying joint, contact, or connection, measured in micro-ohms. A loose or corroded busbar joint, a worn circuit breaker contact, or a poorly made cable lug presents a resistance of only tens or hundreds of micro-ohms, but at full load current that small resistance dissipates real heat, and heat is what eventually fails the connection. Measuring it reliably requires a four-terminal Kelvin measurement that eliminates the resistance of the test leads themselves, and a test current high enough to break through the surface films that would otherwise give a falsely high reading.

The Megavar micro-ohmmeter hire fleet is built on the Megger DLRO range, the established low-resistance ohmmeter family across Australian utilities and contractors. The fleet spans test currents from the portable 10 A handheld instrument, suitable for the bulk of contact and joint resistance work, up to high-current sets that drive the larger test currents some contact resistance specifications and high-current busbar joints require. Every instrument uses a four-terminal Kelvin measurement to eliminate lead resistance, and the higher-current units apply a forward and reverse current technique to cancel out standing thermal EMFs at the contact. Results store on the instrument and download for trend comparison against previous measurements on the same connection. Hire from our offices in Hobart, Launceston, Adelaide and Newcastle, with delivery Australia-wide, from a team that performs contact resistance testing as a regular part of substation commissioning and switchgear maintenance scopes.

Circuit breaker contact resistance

Contact resistance across circuit breaker main contacts is a core commissioning and maintenance measurement. A rising contact resistance indicates contact wear, contamination, or mechanism misalignment, all of which lead to overheating under load. The measurement is taken across the closed contacts with a high test current, and compared against the manufacturer acceptance figure and against previous results on the same breaker.

Busbar, joint, and connection resistance

Bolted busbar joints, conductor connections, and cable lugs are measured to confirm the joint resistance is within specification and consistent across like joints. An outlier joint is the early warning of a connection that will overheat in service. High-current sets are used where the joint carries high current and the specification calls for a representative test current.

Weld, bond, and earth connection integrity

Low-resistance measurement confirms the integrity of welds, equipment bonds, and earth grid connections, distinguishing a sound bond from one that is mechanically tight but electrically poor. This is routine on substation steelwork, earth grid commissioning, and equipment earthing verification.

Commissioning verification on substation and renewable plant

Contact and joint resistance verification is a normal hold point in substation, solar farm, wind farm, and BESS commissioning. Megavar engineers perform these measurements as a regular part of commissioning scopes, which is why the hire fleet is maintained to commissioning standard.

• You need a high-current ductor set for a single commissioning or maintenance campaign
• Capital is constrained or the project rate does not justify outright purchase
• Calibration and freight on owned equipment would exceed hire cost over the project life
• You need to scale several instruments in parallel during a multi-bay switchgear commissioning

• Your team performs contact resistance testing on more than 60 days per year
• You have in-house engineers competent on four-terminal high-current measurement
• You can amortise the unit over its service life
• Your asset programme commits to a multi-year contact resistance trend baseline
• You require permanent on-call availability that hire cannot guarantee

Megavar is a specialist HV testing and commissioning firm with offices in Hobart, Launceston, Adelaide, Newcastle and Gladstone. We perform contact and joint resistance testing as a regular part of substation commissioning and switchgear maintenance work for ElectraNet, TasNetworks, Downer, Acciona, Zinfra/Jemena, and renewable energy developers across Australia. The hire fleet exists because we built it for our own commissioning teams first, and we maintain it to the standard those teams require.

When you hire micro-ohmmeter and ductor testing equipment from Megavar you receive: full current calibration with traceable certificates, the complete current and potential lead set, and a configuration tailored to your scope. Where the project demands a turnkey contact resistance survey rather than equipment hire alone, we can quote on the full service. Hire periods are flexible from a single-day commissioning check through to multi-month maintenance campaigns. Delivery is Australia-wide. Call 1300 730 499 or email rentals@megavar.com.au.

Ductor testing is the field name for a low-resistance measurement, taken with a micro-ohmmeter, that measures the true resistance of a current-carrying joint, contact, or connection in micro-ohms. The name comes from the original Ductor instrument, and the term is still used across the industry for any contact or joint resistance test. It is used to confirm circuit breaker contacts, busbar joints, cable connections, and bonds are sound, because a high-resistance connection overheats under load and eventually fails.

Contact resistance testing measures the resistance across a closed electrical contact, most commonly a circuit breaker main contact, using a micro-ohmmeter at a defined test current. A rising contact resistance over successive tests indicates contact wear, contamination, or mechanism misalignment. The result is compared against the manufacturer acceptance figure and against previous measurements on the same contact, which is the basis of condition-based switchgear maintenance.

At the micro-ohm level, the resistance of the test leads and the contact resistance where the probes touch the connection are far larger than the resistance being measured, so a two-wire measurement is meaningless. A four-wire Kelvin measurement injects current through one pair of leads and measures voltage through a separate pair, so the lead and probe-contact resistance carry no measurement current and do not affect the result. Every instrument in the Megavar fleet uses a four-terminal Kelvin measurement.

The required test current depends on the acceptance specification for the asset. Many circuit breaker and switchgear specifications call for a test current of 100 A or higher so the measurement is representative of the contact under load and breaks through any surface films, while routine joint and connection work is often satisfied by a 10 A instrument. The Megavar fleet spans 10 A, 100 A, 300 A, and 600 A so the test current can be matched to the specification.

Standing thermal EMFs at the junction of dissimilar metals in a connection can add a small DC voltage that biases a low-resistance measurement. The forward-reverse current technique takes a measurement with the current flowing one way, then again with it reversed, and averages the two, which cancels out the standing EMF and gives a true resistance. The higher-current instruments in the Megavar fleet apply this automatically.

Yes. Low-resistance measurement confirms the integrity of welds, equipment bonds, and earth grid connections, distinguishing a connection that is mechanically tight but electrically poor from a sound one. This is routine on substation steelwork and earth grid commissioning. Note that earth grid resistance to remote earth is a separate measurement requiring an earth resistance tester, not a micro-ohmmeter; the micro-ohmmeter verifies the connections within the grid.

Yes. Megavar performs contact and joint resistance testing using the equipment in this rental fleet as a regular part of substation commissioning and switchgear maintenance, including test set-up, on-site execution, and result interpretation against manufacturer acceptance figures. If your project requires a turnkey survey rather than equipment hire alone, contact us with the asset type, the acceptance specification, and the test window, and we will quote a full scope.