In the context of diagnosing fluctuating readings in hot runner systems, the primary method for verifying the adequacy of grounding resistance is to use a specialized ground resistance tester (such as one employing the three-point method or the clamp-on method) to measure the resistance value of the entire grounding loop, and to determine whether this value is ≤ 4Ω. Standard multimeters are incapable of accurately measuring such low-resistance grounding values; therefore, professional equipment is mandatory to obtain reliable data.
Steps for Verifying Grounding Resistance Adequacy
1. Select an Appropriate Testing Method
Three-Point Method (Recommended; High Accuracy):
Suitable for the precise measurement of independent grounding electrodes.
Requires the installation of two auxiliary electrodes: a current electrode (placed 40m away from the ground under test) and a potential electrode (placed 20m away from the ground under test).
Connect the instrument according to its instructions: connect terminal E to the ground under test, terminal P to the potential electrode, and terminal C to the current electrode.
Activate the tester and record the resistance value once it has stabilized.
Clamp-on Method (Convenient; No Auxiliary Electrodes Required):
Suitable for multi-point grounding systems; does not require disconnecting any connections.
Simply clamp the ground resistance tester around a single grounding down-conductor to obtain a direct reading.
Operation is rapid, though results may be susceptible to interference from surrounding grounding loops; therefore, this method is best suited for preliminary screening.
2. Perform the Measurement
Ensure the system is de-energized prior to testing to avoid the risks associated with live-line work.
Clean the grounding terminals and the contact surfaces of the test probes to remove any oxide layers or dirt, thereby ensuring good electrical conductivity.
Set the measurement range according to the instrument's specifications; if using a manual-crank tester, rotate the generator handle at a speed of 120 rpm or higher; if using a digital instrument, wait for the device to automatically complete the sampling process.
Record the final grounding resistance value displayed on the instrument.
3. Determine Whether the Result is Acceptable
Acceptance Criterion: Grounding resistance ≤ 4Ω. This is the general safety standard for low-voltage power systems.
If the measured value exceeds 4Ω, it indicates a poor ground connection, which may be caused by one or more of the following factors:
Corrosion of the grounding electrode or insufficient burial depth;
Loose connection bolts or oxidation of contact surfaces;
Dry soil conditions resulting in poor electrical conductivity.
Certain specialized environments-such as computer server rooms-may impose stricter requirements (e.g., ≤ 1Ω).
4. Use Ground-to-Earth Voltage as an Auxiliary Diagnostic Tool
Even if the grounding resistance meets the specified standard, it is still necessary to measure the AC voltage between the negative terminal of the thermocouple and the ground (earth). If the voltage exceeds 1 V AC, interference caused by ground potential differences may still be present; it is necessary to verify whether a single-point grounding scheme is being utilized.
Practical Tip: Prioritize performing three-point measurements while the equipment is shut down to ensure data accuracy; for routine inspections, a clamp meter can be used for rapid screening.
