Electronics > Mechanical & Automation Engineering
Over-current protection for a 220V motor
pcm81:
I am sizing up a magnetic starter for my 4HP air compressor. I have Eastwood QST30/60 compressor and it is supposed to pull 17A on 220V single phase. What value should i set the mag starter over-current switch? Is there a an equation or a percent rule like 120% of rated current should be a cut off?
Thanks ahead
EDIT: Eastwood claims it to be a 4HP motor, but the 17A current they are advertising is more inline with 3HP single phase draw... so who knows...
The only way i can get 17A draw on 4HP motor is if it is only 80% efficient.
Doctorandus_P:
As far as I know, those motor switches are normally set to the nominal motor current, and they have built in mechanism (usually a bimetalic switch) that allows for short duration over currents. But if your application allows it, you can set it to a bit lower current. With this you may also be able to catch some faults that cause increased friction.
4kW / 220V = 18.18A. If you want horses, then give them some hay or grain. Horses and cows are much more sensitive to electricity then humans because their hooves are so far apart. Especially for things like ground current due to nearby lightning strikes.
themadhippy:
--- Quote ---4kW / 220V = 18.18A
--- End quote ---
were'd 4 kw come from, 4HP is around 3kw.
BrokenYugo:
Air compressors all claim silly power figures, go by the data plate amperage, or use a clamp meter and see what it pulls near your set cutoff pressure.
Google AI hallucinations claim the overload setup varies by manufacturer, some trip at set point, others trip at something like +25% indicated to add in an overload factor for you. Read the manual.
Doctorandus_P:
--- Quote from: themadhippy on September 09, 2024, 11:41:51 am --- 4HP is around 3kw.
--- End quote ---
Are you sure about that? I thought 4HP was about 4 bushels of hay per day.
https://en.wikipedia.org/wiki/Metrication_in_the_United_States
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