Contact resistance measurement :

Mechanical wear and heat on circuit breaker contacts reduces the area of contact surface.

Due to arcing, carbonized layers are built on the contact surface. This also reduces a live contact area.

Reduced contact surface leads to increased contact resistance

R = r*l =ρ / S * l

Increased contact resistance leads to increased heating and losses.

CurrentContact resistancePower loss
10 kA1 mΩ100 KW
1 kA10 mΩ10 KW
10 kA1 mΩ1 Kw
1 kA10 mΩ100 W

At 10 kA a contact with the resistance 0.1 mΩ gives a power loss of 10 kW. This power loss in one single point will definitely confer a temperature rise, which may result in overheating and possibly premature failure.

A strict reading of Ohm’s Law does not indicate the need for the high current

Standards proscribe the following:

IEC56 (IEC62271-100) : 50 A ≤I

ANSI C 37.09 : 100 A ≤I

The higher the current the better accuracy

Pollution of the contact surface

Kelvin’s (4-wire) method

IEC 61227-1 standard recommends use of higher currents in case of increased contacts resistance (more than 100 A).

Very high output voltage enables:

Use of thinner / longer cables

Wider range at high currents

Both Sides Grounded feature


- Safety reasons


- Using current clamps

Optimal measurement parameters:

Accuracy: ±(0,1% rdg±0,1% FS)

Best resolution: 0,01 µΩ

Measuring with use of short cables

Measuring with use of long cables

Traditional measurement method (from the ground)

Measuring with use Kelvin’s probes

Specially designed Kelvin’s probes with trigger button for starting test

Amperis products measuring low resistances (Microhmmeters). The equipment detects low resistances in order to verify safety and reliability in electrical networks. All our products are very accurate and of excellent quality.