ECN Forum Forums General Topics of the Trade General Discussion Area knob and tube wiring

The non-contact indicator is perfect for identifying the hot on K&T provided that there's no load on the circuit in question. That way the neutral won't be energized, and won't show as "hot".
One has to unplug everything from the circuit in question,and the lights need to be turned off. The only possible load that I can see coming back on the neutral in that case would be a transformer such as the doorbell or a smoke detector.

If you know the non-contact's limitations, it can be an invaluable tool. It only indicate the presence of voltage (try one beneath overhead HV lines sometime).
It's not the only tester that you need to carry on your truck, but it does have its uses.

I carry about 10 testers (DVM,analog meters,solenoid type testers,etc.), use them all, depending on the circumstances at the time, and never, never put my trust in any one of them alone to verify the absence of voltage.

Analog multimeters can still show false positives, but usually in the form of weird ghost voltages because they are Hi-Z meters. They have a high impedance designed to keep influence on the circuit being measured as low as possible. This is great for electronics with low voltages where a current flowing through the meter could cause a significant voltage drop), and to some extent for line voltage too (where a current flowing through the meter from hot to ground could trip a GFI) but on the other hand those meters can show ghost voltages caused by induction or capacitive coupling that would vanish if a current flowed through the Lo-Z meter. Unless I want to know the exact voltage +/- a few volts I have been able to work quite nicely with just a Lo-Z meter with a bunch of neon lamps or LEDs indicating different voltage levels (12, 24, 48, 120, 230, 400V) that allows to switch off the load resistor for Hi-Z measuring.

Yeah, been fooled by the ghost V thing Tex

so basically what can we say?

we don't trust testers

there's a big surprise...

and what do we do as a final test?

touch the wire to ground? backhand it?

i.e.- everything we were taught NOT to do...

~S~

Ranger...

You must be using a really high quality analog meter...

The cheap junk out of China has never shown me a false positive.

But then it's not bench-tech worthy.

I haven't had one personally so far but I read about a few.
At school I mostly used high-quality analog meters in lab setups, for a simple reason: they were more likely to be intact since I was the only one who used them! All other students preferred DMMs and frequently fried them. After much hair-pulling with one setup that gave seriously odd voltage readings I started to suspect faulty meters, switched to the old analog stuff - and never turned back! Those were mostly Goerz (Germany) and Norma (Austria) meters, probably from the late 70s or early 80s. The DMMs weren't cheap either, mostly Fluke but apparently most of them were destroyed at some point, resulting in quite weird readings.

In house wiring I use a simple neon tester (either across L-N with the load resistor on, across L-ground without the load or just on the hot, working capacitive like a neon screwdriver or if I want to check for over/undervoltage a cheap DMM. The single pole neon testers do occasionally give false positives, but thankfully I never had a false negative so far, not even on a wooden ladder wearing shoes with rubber soles.

well i noticed the poco guys using the base Fluke models , they do resistance or voltage on the same setting

less chance of blowin' it up on R with V

~S~

You really can't blow up a digital meter on the volt/ohm ports as long as you are within the top voltage limit.
It is not like an analog meter in that regard.
On the amps ports you can easily blow the fuse or even the meter in extreme cases, if you get volts in there.

That's what the fuse is for

If you put 480 across the amps inputs of a Fluke 8060A the fuse loses the race on who clears the fault.

... or so I hear

not if you wrap the blown fuse in a piece of tin foil from your lunch like my bro did....

~S~