Three Phase Motors

[trainsleeper]

Hi All.

I have a .5hp three phase pump. I already have a three phase socket in my unit with a D16 breaker.

I realise I need a DOL starter with thermal overload protection. Is it a case of choosing the closest to the values stated on the motor plate (plus a bit of headroom)?

The motor can be wired in star or delta. What's the advantage/disadvantage of doing it one way or the other?

Thanks,

TS.

 

[ricicle]

You need an overload that can be set to match the full load current of the motor exactly.
Look at the rating plate of the motor to see the exact connection details.
It may need to be connected in star if it is a dual voltage motor. If it is a standard star/delta motor then due to it's size it should be able to be connected in delta.

 

[ericmark]

Motor overloads can be built into a contractor or can be separate units and are adjusted to match the plate on the motor. It can also be incorporated into a soft start or inverter the latter allows some speed control of the motor. Direct on line (DOL) not only puts a strain on the supply but also the motor and coupling at 1/2 HP unlikely a problem but does depend on what it is driving.

Star and Delta allows motors to run at two different voltages with small motors often 230 and 400 so with an inverter it would be powered from a single phase set to 230 and with any other starting method it would be set to 400 volt.

With larger motors the voltages will be 400 and 700 volt and by starting the motor from a 400 volt supply wired for 700 volt it reduces the torque at start once up to speed it is rewired to the 400 volt configuration it is referred to as start delta starting. With star / delta starting some times the overloads are set lower than the current on the plate it depends on where the overload is put.

 

[trainsleeper]

Thanks chaps, much obliged.