gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
101216-1008 EST
Smart $:
The heating effect on the supply conductors is not significant in relationship to the very large difference of motor inrush current to steady state current.
When I verified quinn77's voltage drop calculation at 24 A I used 1 ohm/1000 ft which is a miniscule amount over the 0.9989 value at 20 deg C for #10 annealed copper wire. Since the loop is 500 ft the result is 0.5 ohms.
I can expect an induction motor to have maybe 4 to 6 times full load current as an inrush current. Suppose the air conditioner is 15 A steady state, then at 4 times we have 60 A. The incremental change in voltage from this at a 4 times ratio is 30 V. If the ratio is 6 times, then the drop is 45 V. These are only important in that one does not want the motor to be close to its stall point.
If there is an additional load of 9 A at this time, then the drops respectively become 34.5 and 49.5 .
There is also a source impedance looking back toward the source from the main panel. This might be another 1% drop at 25 A, just a wild guess.
One should also consider that loads at the house at the main panel may produce 5 to 10 V drops at that point.
Thus, worst case may be worse than one initially assumes.
.
Smart $:
The heating effect on the supply conductors is not significant in relationship to the very large difference of motor inrush current to steady state current.
When I verified quinn77's voltage drop calculation at 24 A I used 1 ohm/1000 ft which is a miniscule amount over the 0.9989 value at 20 deg C for #10 annealed copper wire. Since the loop is 500 ft the result is 0.5 ohms.
I can expect an induction motor to have maybe 4 to 6 times full load current as an inrush current. Suppose the air conditioner is 15 A steady state, then at 4 times we have 60 A. The incremental change in voltage from this at a 4 times ratio is 30 V. If the ratio is 6 times, then the drop is 45 V. These are only important in that one does not want the motor to be close to its stall point.
If there is an additional load of 9 A at this time, then the drops respectively become 34.5 and 49.5 .
There is also a source impedance looking back toward the source from the main panel. This might be another 1% drop at 25 A, just a wild guess.
One should also consider that loads at the house at the main panel may produce 5 to 10 V drops at that point.
Thus, worst case may be worse than one initially assumes.
.