that happens when the line already being pushed to its capability
I've never heard of a formula for start up added draw
Watts are the product of volts times amps!
compare it to a hose when you open it at first, it doesn't shoot more stream then it can; when it starts
averages always off the first split second with a digital gauge,
your going from 0 to 10 the first split second, averaging 1,2,3,4,5,6,7,8,9 once it reaches 10 your calculating average of 10
that's why the first second with a digital gouge it will get all over the place at first then get the correct average
based on the logic of the tester
one cant run 5 pumps at once of a 15 amp circuit, it will blow