On 4/12/2014 2:21 PM, Tony Hwang wrote:
wrote:
On Sat, 12 Apr 2014 11:37:31 -0700 (PDT), TimR
wrote:

I was removing one of two light fixtures in my shed. It's an old 8
foot fluorescent that hasn't worked since I've lived here. I
intended to unwire it from the junction box.

I turned off the switch and removed both wire nuts. There are six
wires entering the box: two from the source, two from the
fluorescent fixture, two from the other light. Three black, three
white.

Checking them with a meter, I got roughly 20 volts from white to
black, 40 volts from white to ground (assuming an aluminum ladder on
a concrete floor is close to ground), 20 volts black to ground.

That's with a radio shack digital multimeter, and they're notorious
for some phantom voltages, especially with me checking. So i thought
about coming down the ladder and getting out the Simpson. But it's a
pain to dig it out of the basement and untangle the leads and I had
other chores after this one.

So I turned off main power to the shed and checked again. No voltage
present, finished removing the wires.

But I stayed curious about those readings. Any ideas?

Any open circuit will display weird stuff on a digital meter.
If you put a 1 meg resistor across the leads it will be enough to load
down the antenna effect you have in those floating wires and not do
anything to the real reading on power circuits.. Your Simpson (260?)
is probably around 20k/volt so on the 250v scale it puts 5meg load on.
Cheaper analog meters will have a higher circuit loading.
Digital meters use a CMOS front end with virtually zero load. That is
great for electronics, not so much for power circuits.

Hi,
That's reason I still use an old Simpson a lot even tho 3 DVMs are
kicking around. Fluke, Wavetek.

Fluke makes a small cube that plugs into the meter and the leads plug
into the cube. It puts a much lower resistance across the leads. The
Fluke works like the Simpson.