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.


On Sun, 18 Dec 2005 04:42:22 GMT, Ignoramus4758
wrote:

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...

i
Bill

www.wbnoble.com

to contact me, do not reply to this message,
instead correct this address and use it

will iam_ b_ No ble at msn daught com

In article ,
"William B Noble (don't reply to this address)"
wrote:

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.


On Sun, 18 Dec 2005 04:42:22 GMT, Ignoramus4758
wrote:

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!

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.

--
Free men own guns, slaves don't
www.geocities.com/CapitolHill/5357/

On Sun, 18 Dec 2005 06:28:24 +0000, "William B Noble (don't reply to
this address)" wrote:

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.

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.

"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. "

Could you go into further detail on that RC circuit that you used?

I (and I assume others) would like to measure startup currents on the
RPCs that we are building.

TMT