Re: motor starting relay


"Maxwell" <luv2fly99@xxxxxxx> wrote in message
news:JwTuh.18131$8U4.9385@xxxxxxxxxxxxxxx

Well now, it does have a 5 hp contactor that works off a pressure switch
now. On at 150 psi, off at 175 psi. That contactor makes connection of the
two 120v legs that supply power. But it also has a spring loaded switch
that switches out the starting capacitors at about 1400 rpm or so, it's a
17XX rpm motor. The 5 hp contactor and power leads to the motor are
something different.

The relay I want to ad would switch on the starting capacitors immediately
when the power is switched on by the existing 5 hp contactor, and break
that connection about 1.5 seconds later. So although I know the main
contactor has to be rated for switching a 5 hp single phase motor, that
normally draws 23 amps ( nd has a lock rotor rating of much much more), I
don't know how much amperage is being supplied through, and has to be
broken, by the capacitor circuit. Now that I think about it, it's only
about a 14 or 16 gage wire, so it would have to be a lot less aperage than
the power legs though the 5 hp contactor. The contactor closes a 30 amp
circuit wired with #10 copper.

For sure you don't want the contacts to weld together however it may be that
the starting current through the cap start circuit is quite reasonable once
the motor gets up to speed. So any half way reasonable contactor should do
the job OK - inc. a pre owned one!

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Relevant Pages

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