Max rated current demand of the motor and overload unit

[pprendeville]

Just want to find out if this overload unit will be able to be set for the max rated current on this motor. I don't think it will though as it can only be set to 1.6A and the max rated current is 2.1A in delta? Am I right in saying this?

 

[ryanryan]

is it 3phase?
your motor faceplate has 220v @ 2.1a or 380v @ 1.6a

 

[boatnik1]

The full load amps for your motor is 1.2 amps at 380v so if you are running at 380-415v and 3p star connected then the o/l is adequate.
The o/l would only be overloaded if you were running the motor at 220v with 3p delta connections.

 

[pprendeville]

is it 3phase?
your motor faceplate has 220v @ 2.1a or 380v @ 1.6a

yes it's 3-phase.

The full load amps for your motor is 1.2 amps at 380v so if you are running at 380-415v and 3p star connected then the o/l is adequate.
The o/l would only be overloaded if you were running the motor at 220v with 3p delta connections.

How come the full load current (star config 380V) is less than the delta current (220V). I thought ohms law stated that the higher the voltage the higher the current. I=V/R etc. Is the resistance of the windings greater while in star? Prob dumb questions for you guys but I'm just starting out. Appreciate the help.

 

[boatnik1]

The higher the voltage the lower the current.

Easiest way to demonstrate is a transformer (i.e. welder) 38volts out at 100 amps would require a current of 16.5 amps at 230v in. ignoring efficiency.

Someone else will probably explain the formula. I forgot all that stuff over forty years ago.

 

[pprendeville]

The higher the voltage the lower the current.

Easiest way to demonstrate is a transformer (i.e. welder) 38volts out at 100 amps would require a current of 16.5 amps at 230v in. ignoring efficiency.

Someone else will probably explain the formula. I forgot all that stuff over forty years ago.

Ah no, I was being a bit thick. Sure if the number above the line increases then I will have to be smaller. Doh. Could also use the gear train to illustrate your point. Thanks for the help.

 

[boatnik1]

I should perhaps add that motor windings in modern low Kw. motors are typically wound to facilitate use in countries such as the US where 220 per phase is the norm. Larger motors use star delta in a different way to enable a soft start through a star connection with a timed switch overto delta when the motor reaches its rated speed. Both connections at 380/415v. This method is easier on larger motors than a straight DOL start in delta and draws less current .