dol starter overload calculation?

[Lukusss]

How would i calculate the overload setting needed for a 3 phase 0.5kw dol motor?

 

[m4tty]

Using ohms law to get the amperage then set the overload mate

 

[UNG]

Power equation I = P ÷ V so your looking at 1.25A

 

[davelerave]

Its 3 phase so formula is:
I = kW / ( √3 x pf x VLL ), in kA


For 3 phase Kw to Amps without power factor I divide the Kw rating by 0.692 - the result is in Amps. 0.72A in this case.

and efficiency


better to read the nameplate if possible

if it's a manual starter overload could be 90% of FLA


500w /1.7/400/0.75pf/0.7eff=1.37 amp line current approx

 

[thepurple1]

get the FLA off the rating plate on the motor and set your overload to 110% above that

e.g 10 amp motor 10x110%=11 so set the overload to 11 amps.

 

[johnboy6083]

what we used to do was run the motor/pump at full load and then tong the cables. then set the starter 10% above that.

 

[davelerave]

what we used to do was run the motor/pump at full load and then tong the cables. then set the starter 10% above that.

unlikely you'd be measuring FLA

 

[johnboy6083]

with pumps, we would even half close the valves, so it was the maximum load that the pumps would have under normal service. The we carried out full commsioning of the water features, so any nuisance tripping would be identified within that time. that rule works well.

 

[davelerave]

ya if it's above nuisance level and below FLA it can be don that way

motors can be oversized anyway