0
\$\begingroup\$

I have 380V 3 phase with the following line to neutral voltages: L1: 238V, L2: 234V, L3: 224V. The system has a single phase servo driver that takes in L3 and N, however when hooked up L1, L2, and L3, change to the following: 394V, 400V, 0V. I'm not sure why this discrepancy is happening.

Thanks in advance!

\$\endgroup\$
4
\$\begingroup\$

schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. You have a broken neutral.

\$\endgroup\$
  • \$\begingroup\$ In slightly more detail: you're using three voltmeters with roughly balanced impedances, or there's some conductance and/or capacitance from your local neutral to the neutral reference of your power coming in that keeps things balanced. So when you put that super-high impedance voltmeter on the wires, you read roughly what you should with a connected neutral. But when you hook up an actual load, it overwhelms whatever wimpy connection there is, and just holds L3 at zero volts. \$\endgroup\$ – TimWescott Nov 16 '18 at 19:50

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.