I just started my job as an apprentice technician. For the longest time, my supervisor have always been measuring the amp draws of my motor from the outgoing cable from the motor to the electric panel (which is below the full load amperage stated on the nameplate), but one of our clients insist that the way we've been measuring it is incorrect, and the correct way is to measure the amp draw from the cable incoming to the motor's panel from the distribution panel, which shows that the motor is drawing twice the amps of the FLA.

The motor is a 50Hz 11kW motor with 25.5 FLA.

I haven't found any specific references or examples in my google search, and the closest I've seen is this website https://www.hvachowto.com/measure-amps-blower-motor-condensing-fan-motor/

So, which is the correct way to measure the amp draw of the motor configuration?

Thank very much for any help, and I apologize if the question is too simplistic or stupid to begin with.

  • \$\begingroup\$ Twice the amps? Are you measuring peak? It will also depend on the motor controller. Measuring at motor (properly) will give current going into motor. Measuring at distribution will give current coming from distribution panel. I'm assuming that the controller is in between. I have no experience with 11kW motors or their controllers so can't give any suggestions. \$\endgroup\$
    – Indraneel
    Aug 5, 2020 at 2:29
  • \$\begingroup\$ It depends on whether the motor is single-phase or 3-phase, how the motor is connected and what components of the system are in the motor control panel. An 11 kW, 25,5 amp motor seems likely to be a 400 V, 3-phase motor. If there is more than one wire per phase coming out of the motor, you would need to measure at the input of the control box. However there could be something in the box that would make that inaccurate. You need to know the control details. \$\endgroup\$
    – user80875
    Aug 5, 2020 at 2:35
  • \$\begingroup\$ @CharlesCowie It's a 3 phase motor plugged in to a panel with a Type 2 configuration of thermal protection relay. \$\endgroup\$ Aug 5, 2020 at 3:06
  • \$\begingroup\$ The most likely reason for reading twice the full load amps at the input to the control panel is an error, perhaps mis-interpreting the nameplate. There are other possibilities. I am not going to play a guessing game. You need to study the wiring diagrams in re-check everything. \$\endgroup\$
    – user80875
    Aug 5, 2020 at 11:19
  • \$\begingroup\$ A diagram of the motor and panel connections and where the measurements are made will avoid ambiguity / uncertainty. \$\endgroup\$
    – Russell McMahon
    Aug 5, 2020 at 23:39


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