# Amp probe questions

Discussion in 'Electronic Basics' started by Ryan, Nov 14, 2006.

1. ### RyanGuest

This falls outside the realm of small voltages on small circuits, so
redirects appreciated.

If I am using an amp probe to sense the current flow through wires in a
breaker box and I probe something like 8.33 amps on a 120v circuit (1000
watts) then I believe I can deduce that this consumes a kilowatt in 1
hour and costs me approx \$0.09 at my residential rate.

As I understand North American 240v service, each pole runs 180 degrees
off the other and consumption of current on one side "should" equal the
other. If I probe 8.33 amps on one wire of a 240v circuit (dual pole
breaker) then is this also consuming 1 kilowatt per hour, or do I need
to calculate my reading of 8.33 amps and double it to 16.66?

I'm trying to audit my energy bills compared to ambient electricity
consumption and I'm not certain if I am doing the math properly with the
220v circuits.

When a 220v breaker is rated for 30 amps, is that 15+15 amps or 30+30 amps?

Thank you.

(Very tempted to get an RS-485 adapter, run a 100 foot cable, and start
datalogging my thermostat and graphing HVAC 1st, 2nd, 3rd stage runtimes
and energy costs)

2. ### Michael A. TerrellGuest

30 A per pole.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

3. ### Rich GriseGuest

This consumes one kilowatt, as it's operating. Watts are power, which
is the _rate_ of doing work; work is pretty much the same as energy. In
one hour, a one-kilowatt appliance will have consumed one kilowatt-hour,
which is a unit of energy usage. A 100-watt bulb only uses 100 watts,
but in ten hours, that's a kilowatt-hour.
No. That depends on how well-balanced the loads are on the two sides of
the mains.

And THEY ARE NOT OUT OF PHASE!!!!!!!!!!! THEY ARE PERFECTLY IN PHASE BUT
OPPOSITE POLARITIES! They're the two ends of a center-tapped transformer,
there's no phase-shifting component there.

The power company doesn't like you to run unbalanced loads, but I'd
think that the pole pig (the CT 240V tranny) would compensate for that -
just half its windings would be transferring power.
Well, this isn't exactly the way it works. If it's a ganged breaker, it
will pop if either leg is drawing over 30 amps, but if both legs are
drawing 30 amps, it's just 30 amps through the whole thing and there's
no neutral current. It's like 30 in one wire while 30 goes out the other
wire simultaneously.
My pleasure.

If you're going into that detail, just duplicate this for each phase, and
put in some kind of power factor detection.

Good Luck!
Rich

4. ### Phil AllisonGuest

"Ryan"

** Nope - you cannot deduce that at all.

You need an AC power meter or Kilo Watt Hour ( KWH ) meter to measure
energy consumption.

Depending on the nature of the load and the particular " amp probe " in use,
the figure obtained by making that over simple calculation can be double or
more the actual wattage figure.

BTW

Does " amp probe " = an AC current clamp meter or something else ?

Really helps if you are more forthcoming with important details like this.

........ Phil

5. ### Homer J SimpsonGuest

Do you live in a home, condo or apartment?

6. ### RyanGuest

Depending on the nature of the load and the particular " amp probe "

The reading is obtained with a Fluke T5-1000.

7. ### RyanGuest

Do you live in a home, condo or apartment?

My residence is a house (home).

8. ### RyanGuest

And THEY ARE NOT OUT OF PHASE!!!!!!!!!!! THEY ARE PERFECTLY IN PHASE BUT

I have heard people refer to it as 2-phase and to call 120v service
single phase. I think your assertion makes sense, however.

Is this also true with "3-phase" service, such as commercial delta or
wye configurations? Is it actually 3 polarities or different phases in
that event?

This sounds interesting. Is this done between the meter base and the
panel? I'm curious with what components this is done.

9. ### Phil AllisonGuest

"Ryan"

** Replacing what this smug pig snipped.

" Nope - you cannot deduce that at all.

You need an AC power meter or Kilo Watt Hour ( KWH ) meter to measure
energy consumption. "

** That is an average responding meter - so cannot even give a current VA
figure let alone true power in watts.

......... Phil

10. ### Homer J SimpsonGuest

A single home usually has 240 VAC split into two 120 VAC 'sides'.
A condo or apartment will usually have 2 phases of 3 phase 208 VAC -- 120
VAC line to neutral.

11. ### Homer J SimpsonGuest

Then you should have 120 + 120 = 240 VAC.

12. ### Rich GriseGuest

Yes, 3-phase is actually 3 phases, 120 degrees from each other. They come
from the generator that way - there are three windings that are actually
120 degrees from each other around the circle (or some fraction of that,
depending on the number of poles, but that's a different quesiton.)
Well, I'm thinking a current transformer on each leg, and a voltage
sense, and use a micro to do the arithmetic to get true power and power
factor.

Cheers!
Rich