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'[EE]: Measuring Current'
2002\02\18@182918 by

Donovan submits this for piclist perusal:
> Hello,
>
> Thanks for all the help.  Another question: how do I measure the current
> from a 3-phase, 120Vac voltage source (i.e. a wall plug-in)?

I don't know where you live, but here in the US, the 120VAC electricity that
you would find in a home is single-phase.  But, if that is the type of
current you wish to measure, I suggest you get a "clamp on" type device.
This will save you much trouble and danger.

On the lighter side:

The only guy I ever knew that had 3-phase 440VAC coming into his house was
putting out the REALY BIG signal on 11 meters.  The FCC subsequently removed
his equipment (44,000 watts PEP on AM) amidst much fanfare and cheering by
the neighbors.  This alleviated him of his need for 3-phase power in the
home.

michael brown

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Hello,

I'm up here in Canada and indeed we have single-phase.  Was thinking 3 phase
because of the 3 wires - brain fart.  Anyway, to measure the current can I
put the "clamp on" device in series with any wire?

Regards,
Donovan

> Donovan submits this for piclist perusal:
> > Hello,
> >
> > Thanks for all the help.  Another question: how do I measure the current
> > from a 3-phase, 120Vac voltage source (i.e. a wall plug-in)?
>
> I don't know where you live, but here in the US, the 120VAC electricity
that
> you would find in a home is single-phase.  But, if that is the type of
> current you wish to measure, I suggest you get a "clamp on" type device.
> This will save you much trouble and danger.
>

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> From: Donovan Parks [Donovan.ParksNRC.CA]
>
> Hello,
>
> I'm up here in Canada and indeed we have single-phase.  Was
> thinking 3 phase
> because of the 3 wires - brain fart.  Anyway, to measure the
> current can I
> put the "clamp on" device in series with any wire?
>
> Regards,
> Donovan

Current clamps go around the wire, not in series with anything.  Imagine
attaching a vise-grip to a wire, and then connecting the vice-grip to your
multi-meter.

-Mike

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Dear Donovan,

The great thing about clamp on devices is that you don't put them in series
with anything! You just clamp it around the fully insulated wire without
having to make any changes to the circuit. In the case of measuring the
current drawn from a regular AC outlet, you would want to clamp it on the
hot wire, I'd think, since it is possible for some of the current to flow
in both neutral and ground (although there is a problem if it is flowing in
ground), but the total current must flow in the hot wire.

Clamp on probes work by measuring the magnetic field around the wire due to
the current flowing in the wire; that's why they need no electrical
connection to the circuit. There is a law in electromagnetics that says
that the integral (think average) of the magnetic field around any closed
loop is equal to the current flowing through the hole in the loop times a
constant (which is a fundamental constant). That's why clamp on probes are
not position-critical: as long as the sensing coil in the pickup loop goes
around the wire, it will measure properly.

Sean

At 04:11 PM 2/18/02 -0800, you wrote:
{Quote hidden}

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No, clamp on meters are design to clamp AROUND he wire carrying the current.
Note though that this is an additive process, the meter will show the SUM of
current going through the cables, so you need to clamp only ONE wire,
clamping both would result in a reading of zero. TTYL

> {Original Message removed}
Donovan says:
> Hello,
>
> I'm up here in Canada and indeed we have single-phase.  Was thinking 3
phase
> because of the 3 wires - brain fart.  Anyway, to measure the current can I
> put the "clamp on" device in series with any wire?

The "clamp on" types don't actually have "live" current going thru them.
They inductively measure the amount of current flowing thru the wire.  It
does this by measuring the magnetic field around the conductor.

http://www.appatech.com/a-30.htm  <--- A picture is worth a thousand words

michael brown

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Herbert Graf wrote:

>No, clamp on meters are design to clamp AROUND he wire carrying the current.
>Note though that this is an additive process, the meter will show the SUM of
>current going through the cables, so you need to clamp only ONE wire,
>clamping both would result in a reading of zero. TTYL
>
Unless you're making the reading in a bathtub... ;-)

Adam

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