47 VAC at ceiling box
 

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

47 VAC at ceiling box
 

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

47 VAC at ceiling box
 

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

47 VAC at ceiling box
 

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

47 VAC at ceiling box
 

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