Electricians' toolbox

Rules of Thumb

• At 575 volts, a 3-phase motor draws 1 amp per horsepower.
• At 460 volts, a 3-phase motor draws 1.27 amps per horsepower.
• At 230 volts, a 3-phase motor draws 2.5 amps per horsepower.
• At 230 volts, a single-phase motor draws 5 amps per horsepower.
• At 115 volts, a single phase motor draws 10 amps per horsepower.

  * These above are approximations.

• 746 watts = 1 HP

How to figure out what phase is a certain circuit number for 3 phase:
A easy way to figure what phase a circuit number is to divide it by 6. If it divides evenly it is always "C" phase.

Lets say you have circuit number 27. Divide it by 6. Six will go into 27 four times with a reaminder of 3. Normally panels are labeled with the odds on the left and the evens on the right (see Panel layout example below). So 3 is the second one down from the top on the odd side, so therefore it will be "B" phase. Let's try another one; Say your circuit number is 50. Divide it by 6. Six will go into 50 eight times with a remainder of 2 . So the correct phase for circuit 50 will be "A" phase. This is taken in consideration if the the 3 phase system is phased A,B,C left to right, top to bottom. This is the normal phasing of a system.

Left Hand Generator Rule:
Can be used to to determine the relationship of the motion of the conductor in a magnetic field to the direction of the induced current. To use the left hand rule, place the thumb, forefinger, and center finger at right angles to each other. The forefinger points in the direction of the field flux, assuming that magnetic lines of force are in a direction of north and south.. The thumb points in the direction of thrust, or movement of the conductor, and the center finger shows the direction of the current induced into the armature. Here is a easier way to remember this:

• Thumb = Thrust
• Forefinger = Flux
• Center finger = Current