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measuring current in a 220 ac circuit

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measuring current in a 220 ac circuit kpg 08-13-2007
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Posted by kpg on August 13, 2007, 10:21 pm
Hi all. A simple electrical question (I hope).

I have a clamp on amp meter and I'm interested in seeing how much
current
is used at various loads by the feeder line running to my remote
garage.

The feeder is has 2 hots and 1 neutral going to a sub panel that
divides it
into several 110 circuits.

I know that the current on the neutral will be the difference between
the current on
the two hots (less any stray current lost to the grounding rod), but
I'm interested in
knowing the 'total' amps of the 220 circuit.

I'm thinking I could measure the current on one hot, then on the other
hot, and add
the two values together. What I would like to do is install a
permanent meter but
now I'm thinking that I need two, one for each hot. If I try to
measure the current
by passing both hots through the 'clamp', since they are 180 degrees
out of phase,
won't they cancel each other out (and I would end up with the
difference of the
two like on the netural)?

So my long winded question is this - how can I use a single 'clamp-on'
style meter
to measure current on a 220vac circuit?

Thanks.


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Posted by CJT on August 13, 2007, 10:26 pm
kpg wrote:
> Hi all. A simple electrical question (I hope).
>
> I have a clamp on amp meter and I'm interested in seeing how much
> current
> is used at various loads by the feeder line running to my remote
> garage.
>
> The feeder is has 2 hots and 1 neutral going to a sub panel that
> divides it
> into several 110 circuits.
>
> I know that the current on the neutral will be the difference between
> the current on
> the two hots (less any stray current lost to the grounding rod), but
> I'm interested in
> knowing the 'total' amps of the 220 circuit.
>
> I'm thinking I could measure the current on one hot, then on the other
> hot, and add
> the two values together. What I would like to do is install a
> permanent meter but
> now I'm thinking that I need two, one for each hot. If I try to
> measure the current
> by passing both hots through the 'clamp', since they are 180 degrees
> out of phase,
> won't they cancel each other out (and I would end up with the
> difference of the
> two like on the netural)?
>
> So my long winded question is this - how can I use a single 'clamp-on'
> style meter
> to measure current on a 220vac circuit?
>
> Thanks.
>
Run one through in the opposite direction.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.

Posted by CJT on August 13, 2007, 10:27 pm
CJT wrote:

> kpg wrote:
>
>> Hi all. A simple electrical question (I hope).
>>
>> I have a clamp on amp meter and I'm interested in seeing how much
>> current
>> is used at various loads by the feeder line running to my remote
>> garage.
>>
>> The feeder is has 2 hots and 1 neutral going to a sub panel that
>> divides it
>> into several 110 circuits.
>>
>> I know that the current on the neutral will be the difference between
>> the current on
>> the two hots (less any stray current lost to the grounding rod), but
>> I'm interested in
>> knowing the 'total' amps of the 220 circuit.
>>
>> I'm thinking I could measure the current on one hot, then on the other
>> hot, and add
>> the two values together. What I would like to do is install a
>> permanent meter but
>> now I'm thinking that I need two, one for each hot. If I try to
>> measure the current
>> by passing both hots through the 'clamp', since they are 180 degrees
>> out of phase,
>> won't they cancel each other out (and I would end up with the
>> difference of the
>> two like on the netural)?
>>
>> So my long winded question is this - how can I use a single 'clamp-on'
>> style meter
>> to measure current on a 220vac circuit?
>>
>> Thanks.
>>
> Run one through in the opposite direction.
>
Oh, and divide by two.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.

Posted by Toller on August 13, 2007, 10:35 pm

> Hi all. A simple electrical question (I hope).
>
> I have a clamp on amp meter and I'm interested in seeing how much
> current
> is used at various loads by the feeder line running to my remote
> garage.
>
> The feeder is has 2 hots and 1 neutral going to a sub panel that
> divides it
> into several 110 circuits.
>
> I know that the current on the neutral will be the difference between
> the current on
> the two hots (less any stray current lost to the grounding rod), but
> I'm interested in
> knowing the 'total' amps of the 220 circuit.
>
> I'm thinking I could measure the current on one hot, then on the other
> hot, and add
> the two values together. What I would like to do is install a
> permanent meter but
> now I'm thinking that I need two, one for each hot. If I try to
> measure the current
> by passing both hots through the 'clamp', since they are 180 degrees
> out of phase,
> won't they cancel each other out (and I would end up with the
> difference of the
> two like on the netural)?
>
> So my long winded question is this - how can I use a single 'clamp-on'
> style meter
> to measure current on a 220vac circuit?
>
If you created a loop so that you simultaneously measured one hot backwards
and one forwards it ought to work.
(actually I don't know, but it seems like it should)

Why do you want to do this anyhow? The information is pretty useless.



Posted by kpg on August 13, 2007, 11:02 pm
> Why do you want to do this anyhow? The information is pretty useless.- Hide
quoted text -

Well, I can't argue with you there. For one, I like gadgets. For
another, I have
a 5hp compressor, some computer equipment, a full time window unit,
and
a part time window unit, a bunch of fluorescent lights, occasionally a
hand drill
or table saw.

It all runs on a 30 amp branch circuit and at times the breaker gets
quite
warm to the touch. I thought it would be nice to be able to monitor
the load on the system, i.e., the amps flowing through the feeder
line.

And did I mention I like gadgets?

I'll do some experiments with the one backwards divide by two
method.




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