Regarding -submersible residential style water pump relays- pumps fitted with a three wire cable which terminates into a submersible pump relay box--the red wire feeds the starting winding in the pump motor.

I understand the orange wire coming from the capacitor feeds across the relay contact, down the red wire to the starting winding. After the pump motor starts the contact drops out.

The ?-- Do those submersible pumps have drop out clutches or the like that fault the 'red wire starting feed' to the pump well casing, after motor starts, perhaps? I understand that would be an induced 'ground fault'of the sorts but it would be momentary and would create that difference of potential to allow relay to drop out contact. Attempting to understand what happens down at the motor, that creates that difference of potential needed for the yellow hot, to feed through the coil? enter image description here enter image description here

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As far as I know, all the switching for these is done at the control box. Rather than a centrifugal switch, I believe the relay is simply a fixed time-delay contact.

But I consider them archaic these days - For single-phase supply, I buy 2-wire pumps, and would replace any 3 wire pump with a 2-wire pump when the 3-wire pump stopped working. The arguments in favor of 3-wire have become much like arguments in favor of a buggy-whip to make your automobile go faster...

If 3-phase supply is available that's a whole different animal, but it's uncommon for residential applications where I live.

  • 'Fixed time delay'.-ok. At anyrate, that has to be accomplished by allowing voltage to flow through the coil to a lower potential diff in order to create the magnetic field needed to pull that contact 'open'...because that's all this control box is that relay you see above. The relay only contains a small coil and that single contact.
    – amp-here
    Mar 9, 2017 at 19:57

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