Did a little experiment... I clamped a clamp on ammeter on the single phase supply wire for my 10 HP idler, and flipped the switch to start it. It started as always, but to my amazement, the ammeter showed the current shooting all the way up to 120 amps! That was for a second or less. The regular running current (probably at a low power factor) was something like 12 amps.
So, the starting current was 10 times the running current!
Now I know why the lights dim a little...
iAnd why pony motors make sense for the big ones, they don't just dim your lights but everyone's on the same transformer! After getting close to the running rpm the large motor I start does NOT dim even my lights, I have never measured the amps that the motor needs to get up to full speed but I would guess 50-60 amps do it. Next time I start mine, and have a clamp ammeter handy I will check.
or maybe you know why you can't trust clamp on ammeters for high frequency one shot measurements? Do a calculaton of voltage drop and see, given the resistance of the wires from the pole to you, if 120 amps is possible on that particular circuit.
Bill
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I cannot see why it is not possible, momentarily. I have 6 gauge wire on a 60 amps breaker. The length of the circuit is about 75 feet from the main panel. I once calculated that at 100 amps, the energy loss in the circuit would be 750 watt.
i
Not unusual to have starting current 10x running, that's what I measured on my 'high efficiency' refrigerator. I didn't have a clamp-on at the time so I used a DC voltmeter with a RC circuit and had no trouble reading the peak current.
Not at all out of line as far as inrush currents go. Might be why some of the geezers spin their idler up with a rope before cutting in the juice.
Hey. I resemble that remark...
Jim
It's possible. I've observed about 200 amp starting current on a 2 HP 110-volt 3450 RPM induction motor (buffer) using a current transformer and an oscilloscope.
If anything, a clampon meter will read low on transients because of it's damping.
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