Clamp Meter Test Motor and Motor Control Circuit
One of the most challenging places to make current measurements is the control cabinet, especially if it uses IEC type components. IEC type parts of European origin are much more compact than the corresponding NEMA parts, and the wiring may be quite tightly packed. The Fluke 330 Series clamp drives fan and pump loads. The motor can be controlled by an electromechanical starter, or by an electronic variable speed drive. Variable speed drives are becoming more common because they save a lot of energy.
q is the ideal clamp meter for the following motor and drive measurements:
Load Sizing: The motor sink current measured as an average of three phases should not exceed the motor's full load current rating. The tapered clamp and backlight features of the table are well suited for this measurement task. Multiplied by the allowable overload factor'
On the other hand, motors with load currents below 60% of full load current (and most do) are increasingly inefficient and power factor drops.
Current balance: A current imbalance may indicate a problem with the motor windings (for example, different resistances across the field windings due to an internal short circuit (generally, the imbalance should be below 10 %. (To calculate the imbalance, first calculate the three-phase average of the readings; then find the maximum deviation from the average and divide by the average.) Extremely high current imbalances are single-phase unbalances when one of the three phases has no current flow. This is usually caused by an open fuse cause.
Inrush current: Motors that are started directly under pressure (via a mechanical starter) have an inrush current (inrush current can reach approx. Causing voltage sags and annoying trips. The "Inrush Current" feature of the clamp meter is a unique feature designed to trigger on inrush current and capture its true value.
Peak Loads (Shock Loads): Some motors experience shock loads that can cause a current surge sufficient to trip the overload circuit in the motor controller.
Imagine running into a hard-knotted chainsaw. The MIN/MAX function can be used to record the worst case current drawn by the surge load.
Clamp meters are an indispensable tool for electricians in both residential and commercial installations.
