Accurate Method For Detecting Contact Resistance Of Neutral Blocks

The detection of contact resistance of neutral blocks requires high-precision methods to ensure measurement accuracy. The four wire method (Kelvin measurement method) is the core recommended technology, and its principle and operating points are as follows:

1、 The principle and advantages of the four line method

The four wire method eliminates the influence of test lead resistance on measurement results by separating the current path from the voltage measurement path. In the specific operation, two current leads are used to apply a constant current to the tested terminal, and the other two voltage leads are tightly attached to both sides of the contact point to measure the true voltage drop. Due to the extremely high impedance of the voltage measurement circuit (usually>1M Ω), the influence of lead resistance (usually<100m Ω) on the results can be ignored, thus achieving accurate measurement of micro ohm (μ Ω) level resistance.

2、 Testing equipment and parameter settings

Device Selection

Priority should be given to using micro ohmmeters (such as Agilent 34420A), which have a resolution of up to 0.1 μ Ω and support four wire measurement; If there is no dedicated equipment, an advanced digital multimeter (such as Puyuan Jingdian DM858) can also be used, but it should be noted that its accuracy may be lower than that of a micro ohmmeter.

Parameter Configuration

Current range: Select according to the rated current of the terminal, usually between 1A and 10A, to avoid high current causing contact surface heating and affecting the results.

Voltage range: set to millivolts (mV) to match the small voltage drop generated by contact resistance.

Sampling time: extended to 5-10 seconds to reduce the impact of transient fluctuations on readings.

3、 Operation steps and precautions

preprocessing

Clean the contact surface of the terminal, remove the oxide layer or dirt, and ensure good contact.

Check the test leads to ensure no breakage or poor contact.

Connection and measurement

Connect the current leads to both sides of the terminal, and ensure that the voltage leads are tightly attached to the contact points (spacing<1mm).

Turn on the device, record multiple measurements (recommended ≥ 5 times), and take the average to improve repeatability.

environmental control

Conducted in a constant temperature (25 ℃± 5 ℃) and dry (humidity<60%) environment to avoid fluctuations in material resistivity caused by temperature changes.

Avoid vibration or external interference during the measurement process to prevent errors caused by changes in contact pressure.

4、 Result analysis and improvement

standard comparison

Compare the measured values with industry standards (such as GB/T 14048.7) or equipment manufacturer specifications. For example, the contact resistance of industrial neutral blocks is usually required to be ≤ 5m Ω, and the rate of change after temperature rise is ≤ 20%.

exception handling

If the measured value exceeds the standard, check whether the contact surface is flat and whether the coating is complete. If necessary, re press or replace the terminal.

For high-frequency usage scenarios (such as switchgear), it is recommended to conduct regular inspections (every 6-12 months) to prevent the risk of heating or fire caused by poor contact.