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can anyone explain to me how the answer is derived from this information

The ohm readings taken from a hermetic compressor are 12 ohms from R to ground, 6 ohms from C to ground, 6 ohms from S to ground, 18 ohms from R to S, 6 ohms from R to C and 12 ohms from S to C.
a)  The compressor has a small short to ground half way through the run winding.
b)  There is a small short to ground half way through the start winding.
c)  There is a small short to ground half way through common winding.
d)  There is a small short to ground in the internal overload.


6 ohms S - G
12 ohms S - C

18 ohms R - S
6 ohms R - C
12 ohms R - G

6 ohms C - G

how is it determined that there is a small short to ground half way through the start winding?

The answer is B but its difficult to explain without drawing a diagram. Draw yourself a diagram with the 3 terminals, draw a winding from R-C, draw another winding from S-C (forget about the overload for now) then try to work it through. If it still doesn't make sense, draw in the short in the middle of the start winding and try again. Remember, the windings are still intact, not open, just shorted in the start winding.

thanks, ill try drawing it out, that usually helps make most things make sense.

i found this not sure how true this 3 -6 factor is for determining a partial short.

partially shorted winding

- Measure the ohm value for connection Common to Running and Common to Starting.

- Record the value, example :-

C to R = 0.5 ohm

C to S = 3 ohm

- The formula to determine a winding condition is good,the resistance of starting winding is equal 3 to 6 times of running winding

3 ohm / 0.5 ohm = 6 ( winding for this compressor is good )

- We must remember this formula : "The good winding ohm value must in range between equal 3 to 6 times.If value out off this range,we can assume the winding is shorted and defected."



anyone else use this formula for determining if there is a partial short?

Additional answer that is ( b) is correct. the formula is plus and minus.

Normal Reading
C to R = 6 ohms
C to S = 12 ohms
S to R = 18 ohms

Gnd to C = - : -
Gnd to R = - : -
Gnd to S = - : -

the Question is - 12 ohms from R to ground, 6 ohms from C to ground, 6 ohms from S to ground, 18 ohms from R to S, 6 ohms from R to C and 12 ohms from S to C.

Solotion.

run winding = 6 ohms, in normal reading
run winding to ground = 12 ohms, you add 6 ohms, this additional 6 ohms is from half of start winding that is grounded.

Start Winding = 12 ohms, in normal reading
Start winding to ground = 6 ohms, this means half of the winding is grounded.

Com to ground = normal infinite ohms or no reading. - : -
Com to ground = 6 ohms. this reading is the half of start winding

Faulty Reading
C to R = 6 ohms
C to S = 12 ohms
S to R = 18 ohms

Gnd to R = 12 ohms -  you add 6 ohms, this additional 6 ohms is from half of start winding that is grounded.
Gnd to S = 6 ohms - half of start wingding is gone, this means half of the winding is grounded.
Gnd to C = 6 ohms - half of start winding is here.

thanks that was actually a lot of help. soon as i read that common to ground should read infinite that put me on the right track. i thought before that common to ground to should read run + start added to together.