3PH question

TBoomz

Ron
User
noob question, here. I've read that electric motors have more torque than a GAS engine of similar HP, so am wondering if something similar exits between electric motors [e.g. 3 phase 1.5HP vs single phase 1.5 HP]? Does the 3PH pull stronger?
 

Oka

Oka
Corporate Member
Not stronger more efficient. This gets into how the electricity is being applied to the motor. Also lower amps

3 hp 220 single phase motor will pull close to 28-30 amps. This requires #10 wire and larger breakers to run ... plus single phase is not continuous power.

3 hp 220 three phase motor will pull between 17-19 amps. This will only require #12 wire and regular breakers to run ... plus three phase is continuous power.

Torque is the real thing you need to understand. Torque is how the power is being expressed under work. 1 hp = 3 ft lbs 2 hp = 6 3 hp 9 @ 1725 rpm. At 3450 rm they are roughly 1/2 those numbers but........... things are moving WAY faster to speed becomes an issue with regards to safety.

3 Hp gets to a motor strength that if you are not adept and knowledgeable about how to use a tablesaw correctly, you will get things kicking back into you which sucks to say the least .... or get really injured at the worst.

THe biggest advantage to 3 phase motors besides the better use of electricity is you can run them on a variable frequency driver. THis allows you to just turn a kn ob to run down the rpm with minimal loss of effective power.
 

Willemjm

Willem
Corporate Member
Oka, nice explanation.

Just one point to mention. All my single phase 3hp 240V motors are connected to 20A breakers, no issues.
1hp= 746Watts
3hp= 2238Watts
Current = 2238/240/0.8 = 11.7 Amps
For starting current, unlikely that would go above 15 A

For 3 phase divide the above by square root of three and power factor.
 
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