Motor plate, 2hp, 3 phase, 7amp

That is the motor.

Looks like the old version of a new Baldor M3558 2HP 3phase motor.

I plan to run a 230v 3phase line to the motor, but I need a starter.

This starter on Grainger looks promising: https://www.grainger.com/product/SQUARE-D-Magnetic-Motor-Starter-19YA92

But my motor specs are 7A and 2HP

...and that starter, which is the closest I can find, is 18A and 3HP.

Is it OK to supply that extra 1HP? Is the 18A in the starter to cover for starting voltage?

  • \$\begingroup\$ Given the price of that starter, I'd take a look at a VFD (Variable Frequency Drive) and ask if it's a possible alternative. \$\endgroup\$ Jan 30, 2016 at 23:46
  • \$\begingroup\$ Isn't the 3-phase version of 230V single phases ~400V, in which case it'd be into its 3.5A mode, correct? \$\endgroup\$ Jan 31, 2016 at 2:12
  • \$\begingroup\$ Is that how it works? I thought it was 2hp * 750 watts = 1500 watts / 230 volts = 6.5A \$\endgroup\$
    – Slobvrflw
    Jan 31, 2016 at 2:22

1 Answer 1


When choosing a relay or starter you need

  • Contact voltage rating >= supply voltage, 230 V in your case.
  • Contact current rating >= current drawn by the load. This may be considerably more than the steady running current.

The start won't 'supply' that current in the sense of forcing it into the motor. If, on the other hand, the motor draws or 'calls for' that current you know that the starter is capable of handling it.

Since it is a starter, the manufacturers will have taken the starting surge into consideration. If it's capable of starting a 3 HP motor it will be fine on a 2 HP.

Make sure you've got the right coil voltage for your control circuit.

  • 1
    \$\begingroup\$ You need to make sure the overload relay can be set for 2 Hp. Also note that the starter you linked has a 240 volt coil. \$\endgroup\$
    – user80875
    Jan 30, 2016 at 23:42
  • \$\begingroup\$ I believe this starter comes with a D3 "thermal unit" or the overload relay as stated by Charles Cowie. Grainger doesn't say anything about the thermal unit. Other web sites show D3 as included. Your motor will likely need other thermal unit. Just noticed that Grainger says the starter comes without overload unit. \$\endgroup\$
    – Marla
    Jan 30, 2016 at 23:46
  • \$\begingroup\$ Elsewhere, Grainger shows the OL relay is included. The footnote may mean the heaters for the OL relay are sold separately. You may find a lower price elsewhere if you want to buy on the internet from someone not known as well as Grainger. \$\endgroup\$
    – user80875
    Jan 31, 2016 at 0:04
  • \$\begingroup\$ Here is the heater. You need three for a 3-phase motor.grainger.com/product/SQUARE-D-Thermal-Unit-WP46104/_/N-/… \$\endgroup\$
    – user80875
    Jan 31, 2016 at 0:13
  • \$\begingroup\$ @Charles: Wrap up all of that in a separate answer and get the credit as this is your area of expertise. Thanks for the follow up. \$\endgroup\$
    – Transistor
    Jan 31, 2016 at 0:19

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