I'm reading a book on split start motors where single phase ac is phase shifted by two inductors at different resistance and inductance.

My question is how does this offer a 30-45 degree phase shift, which is what my reading material is showing? I was under the apparent misunderstanding that all inductors and capacitors shift voltage and current by 90 degrees.

With a single phase input shouldn't the current through the inductors be in phase with each other?

  • \$\begingroup\$ where is the "reading material" ? \$\endgroup\$ Sep 3, 2019 at 22:16
  • \$\begingroup\$ I'm reading from various websites and the books that I received when I became an apprentice. This was the site I was reading from when I posted my question. machineryequipmentonline.com/hvac-machinery/… \$\endgroup\$
    – Srmass
    Sep 3, 2019 at 22:39

1 Answer 1


The phase relationship between current and voltage in an ideal inductor is indeed 90 degrees. In an ideal inductor, the impedance would be all reactive, so that the impedance would not have a resistive component. However, in the real world, coils have both a resistive and reactive (inductive) component, so that the phase shift is always less than 90 degrees. In a split-phase motor, the coil windings are designed so that the auxiliary winding has a higher resistance-to-inductance ratio, so its current is phase-shifted a lesser amount than the main winding.


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