I have the ceiling box open for my kitchen light fixture (getting
ready to paint.) With no load across the leads that feed the ceiling
light and the switch off I measure 47 VAC. If I put a 60W bulb across
these leads the voltage goes to zero. When the switch for this fixture
is turned on I get a normal 120 VAC.

Can I assume the 47 VAC is just some coupling from an adjacent
circuit into a high impedance load?

FWIW, this light fixture is serviced by two three way switches and the
color coding does not follow any standard I have seen (there is no
red wire that I have found yet.)


John Keith

John Keith wrote:
I have the ceiling box open for my kitchen light fixture (getting
ready to paint.) With no load across the leads that feed the ceiling
light and the switch off I measure 47 VAC. If I put a 60W bulb across
these leads the voltage goes to zero. When the switch for this fixture
is turned on I get a normal 120 VAC.

Can I assume the 47 VAC is just some coupling from an adjacent
circuit into a high impedance load?

Yes - especially if you are using a digital meter

FWIW, this light fixture is serviced by two three way switches and the
color coding does not follow any standard I have seen (there is no
red wire that I have found yet.)


John Keith

On Wed, 06 Sep 2006 19:33:33 -0500, No Spam
wrote:

Can I assume the 47 VAC is just some coupling from an adjacent
circuit into a high impedance load?

Yes - especially if you are using a digital meter

I am using a digital meter, and I've heard that comment before but
I've never understood why a digital meter responds differently than
an analog meter. Both present a high impedance (11 Mohm?) to
the circuit under test. What is the difference?

John Keith

If they both present the same impedence, then there is no difference.
But a really good analog meter will top out at 20Kohms/v and the
really cheap ones are much less than that. Any old timers will
remember VTVMs (vacuum tube voltmeters) that presented impedences
above 1Mohm/volt. Today's digital meters are all above 1Mohm/v which
is significantly above that of an analog meter.

dickm


On Thu, 07 Sep 2006 07:20:25 -0600, John Keith wrote:

On Wed, 06 Sep 2006 19:33:33 -0500, No Spam
wrote:

Can I assume the 47 VAC is just some coupling from an adjacent
circuit into a high impedance load?

Yes - especially if you are using a digital meter

I am using a digital meter, and I've heard that comment before but
I've never understood why a digital meter responds differently than
an analog meter. Both present a high impedance (11 Mohm?) to
the circuit under test. What is the difference?

John Keith

On Thu, 07 Sep 2006 07:20:25 -0600, John Keith wrote:

On Wed, 06 Sep 2006 19:33:33 -0500, No Spam
wrote:

Can I assume the 47 VAC is just some coupling from an adjacent
circuit into a high impedance load?

Yes - especially if you are using a digital meter

I am using a digital meter, and I've heard that comment before but
I've never understood why a digital meter responds differently than
an analog meter. Both present a high impedance (11 Mohm?) to
the circuit under test. What is the difference?

John Keith


The difference isn't about analog or digital. It's about
high-impedance input circuitry. Most (if not all) digital meters have
it. Some analog meters have it.
--
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Mark Lloyd
http://notstupid.laughingsquid.com

"All your western theologies, the whole mythology of them,
are based on the concept of God as a senile delinquent."
-- Tennessee Williams