Static and dynamic resistance measurements

A static resistance measurement determines the electrical resistance of a component at rest, using a constant DC current. The measurement always uses the four-wire Kelvin method, ensuring cable resistances are eliminated.

This method is the foundation for measuring contact resistance in switches and electrical connections.

Characteristics of a static resistance measurement

Constant DC current
A single stable measurement value
Extremely accurate (micro-ohm to milli-ohm)
Ideal for measurements without mechanical movement

What can you detect?

Loose or poor electrical connections
Contact corrosion
Defective welds
Insufficient contact pressure
Faults in motor or transformer windings
Transition resistances caused by thermal stress
Optimal stability and accuracy for industrial busbar systems

Dynamic resistance measurement does not look at the component at rest, but at its behavior during movement. The test current flows while a circuit breaker or relay opens or closes, and the resistance is continuously logged with high sampling speed.

In practice, dynamic resistance measurement is the main method to assess wear of arcing contacts without disassembly.

High measurement speed (millisecond resolution)
Provides a curve instead of a single value
Reveals both mechanical and electrical degradation
Essential for HV and MV circuit breakers
Detects failures that static measurements will never find

What can you detect?

Wear and erosion of arcing contacts
Mechanical hesitation during travel
Low or unstable contact pressure
Delayed opening or closing
Misalignment in the contact mechanism
Micro-arcing that occurs only during movement

HighTest ARES D Series

Combines static micro-ohm measurement with dynamic resistance analysis
High current + high-resolution logging
Designed for utilities, heavy industry, and service companies
Full DRM capability, not just trend monitoring

Megabras does not support DRM; their instruments are static only.

A common mistake is assuming that a low contact resistance means a breaker is “healthy”.
Many switching issues only appear during the switching operation, not when the breaker is closed.

Therefore, static and dynamic measurements are not alternatives, but complementary.

Megabras: static micro-ohm measurements

Ideal for industrial joints, motors, and busbars
Rugged, compact, and practical
For maintenance teams, service companies, and inspection bodies
Up to 200 A test current with high accuracy
No dynamic measurement

HighTest HARE: heavy-duty static measurements
For large installations and extremely low resistances
High DC currents up to 300 A
Very stable signal and accuracy
Suitable for busbar systems, primary networks, and industry

HighTest ARES D: static and dynamic measurement

Intended for circuit breaker analysis
Real-time resistance curves during opening and closing
Detects arcing-contact wear without disassembly
Adjustable test current from 1 to 200 A
For utilities and HV/MV maintenance

When should you choose which technique?

Choose static measurement when

You test motors, generators, and transformers
You inspect joints, busbars, and welds
You perform routine maintenance
You require highly accurate micro-ohm measurements
Use Megabras or HighTest HARE
For transformer windings, use a winding resistance tester such as the WINRES-20B or TRIORES-20.

Choose dynamic measurement when

You evaluate circuit breakers or relays
You want to detect arcing-contact wear
You need to analyze travel mechanisms
You need to detect deviations that occur only during switching

Industry cannot afford to rely solely on static resistance measurements. Static measurement is essential, but it only shows what happens at rest.

Dynamic measurement reveals behavior during switching, exactly where most failures originate. Dynamic testing is often the only way to detect degradation in arcing contacts and mechanical performance.

This is why a professional testing strategy combines both methods.

With these instruments, IONIO has a suitable instrument for both methods, for industrial connections and for high-voltage switchgear.