Volt meter Question

[King]

Here is my scenerio. I am a Line and Service tech and was going to energize a suspect piece of under ground secondary wire. I megged the cable with a dynatel and it bled out at 700k volts which to me means the cable has some small abrasions but is in good enough shape to carry current. I then took my fluke 12b VOM before energizing the wire and checked contuinity and all 3 wires showed clear. Then set the meter on Volts and it read back red lead on energized phase and black lead to L1-120 volts then L2- 120 volts, and then Neutral 122 volts. My first thought is L1 or L2 is grounded or is there that much resistance in this 100' of 4/0 aluminum connected to 140' #2 aluminum and 40' of 1/0 copper. (the service wire is isolated in the meter base with meter pulled) I then got another VOM a Fluke 116 and it showed the same with the dial on the V- volt setting. I then switched the Volt meter (both of them) to the Auto-V LOz setting which automaticly checks volts, or ohms and it showed on both meters energized phase to new wire 5volts on L1, 5volts on L2, and 122 volts phase to neutral. This is more of what I was expecting on the Volt function. My question is why the VOM did not show this on the Voltage setting? Any enlightment is welcomed.

[Pootnaigle]

If I understand right you were measuring from one phase of the old to a like phase of the new and read a 5 volt difference on each. That to me would suggest the presence of resistance in the unenergized wire.

[wtdoor67]

You overexplained it. Smoke test it.

[King]

If I understand right you were measuring from one phase of the old to a like phase of the new and read a 5 volt difference on each. That to me would suggest the presence of resistance in the unenergized wire.

That is correct 5 volts with the VOM set on Auto-VZ, but when I turn the selector switch to Volts The meter would read 120 volts so my question is; why is the VOM reading different potentials on the same wires when on practically the same setting?

[King]

You overexplained it. Smoke test it.

I know I have put way to much thought and time into it. I just want to know why the difference in readings on the voltmeter on practically the same setting. I wrote the guys at fluke and asked them? I will post when they give me a response.

[wtdoor67]

They're not infallible, check it against other Voltmeters. It's always a good idea to periodically check them for accuracy.

In paralleling it is so common to read a small difference on like phases. I can hardly ever remember getting a perfect zero reading on parallels.

I once asked a relay person who was involved in paralleling some subs together. I asked if they had a rule of thumb for this. He replied their local rule was 6 degrees or less. Admittedly this one you refer to was low voltage, but I bet in a general way this would apply in a lot of situations.

[jozmo]

Here is my scenerio. I am a Line and Service tech and was going to energize a suspect piece of under ground secondary wire. I megged the cable with a dynatel and it bled out at 700k volts which to me means the cable has some small abrasions but is in good enough shape to carry current. I then took my fluke 12b VOM before energizing the wire and checked contuinity and all 3 wires showed clear. Then set the meter on Volts and it read back red lead on energized phase and black lead to L1-120 volts then L2- 120 volts, and then Neutral 122 volts. My first thought is L1 or L2 is grounded or is there that much resistance in this 100' of 4/0 aluminum connected to 140' #2 aluminum and 40' of 1/0 copper. (the service wire is isolated in the meter base with meter pulled) I then got another VOM a Fluke 116 and it showed the same with the dial on the V- volt setting. I then switched the Volt meter (both of them) to the Auto-V LOz setting which automaticly checks volts, or ohms and it showed on both meters energized phase to new wire 5volts on L1, 5volts on L2, and 122 volts phase to neutral. This is more of what I was expecting on the Volt function. My question is why the VOM did not show this on the Voltage setting? Any enlightment is welcomed.Get yourself a Simpson 260 voltmeter , digital sometimes show phantom voltages .

[lineman2010]

They're not infallible, check it against other Voltmeters. It's always a good idea to periodically check them for accuracy.

In paralleling it is so common to read a small difference on like phases. I can hardly ever remember getting a perfect zero reading on parallels.

I once asked a relay person who was involved in paralleling some subs together. I asked if they had a rule of thumb for this. He replied their local rule was 6 degrees or less. Admittedly this one you refer to was low voltage, but I bet in a general way this would apply in a lot of situations.

I have heard the 6 degree thing for paralleling circuits together before. I have also heard of a utility dropping a hewlett-packard plant because there internal devices needed to be 3 degrees or less for paralleling... Opps

[clumsum69]

I know I have put way to much thought and time into it. I just want to know why the difference in readings on the voltmeter on practically the same setting. I wrote the guys at fluke and asked them? I will post when they give me a response.

the difference could be cappasinence(sorry bout the spelling) the new led meters wont bleed it off try an analog meteer

[rob8210]

I don't like digital voltmeters. They can give you screwy readings. Some years ago I almost condemned a transformer for low voltage, then a little voice told me to get a different meter. Turned out the can was good and the battery was getting weak in the voltmeter, thus giving false readings. Now I always carry a second voltmeter with me. And just the other day we were getting ready to parallel two transformers when we got some very strange voltage readings on the new transformer. Turned out buddy had it set on dc volts. Not hard to do when the settings for ac and dc are right beside each other. My advice double check everything, carry a spare meter and spare batteries.

[T-Man]

Digital meters are state of the art but too sensitive for our line of work. The resistance of digital testers is so high they can read electrical pulses in snot so a more simple meter that us calibrated is perfect for line work. Besides in cold weather some of the screens won't show a reading or maybe jumbled unradable displays. I'd go old school and use test lamps for simple tests and maybe an annalog meter for volt reading. A Fluke is a nice meter but you better know and understand how and why it's giving you the reading your getting. Be sure your batteries are up also like stated above.
One year in a Troble Review (we did one every year) we had one of our application Engineers explain the operating, testing and problems encountered with the testers and meters we were using. If your company does something like that it's a good review.

[Pootnaigle]

Ummmmm we done some work in a 69 kv sub on the lighting( 480) and a digital meter showed all kinds of crazy voltage on the lighting circuit once you got into the magnetic feild of the 69.Purdy much useless. Wound up usin a wiggie.. Lol I told an apprentice to wear gloves to work on the lights and he didnt on that first one. He grabbed sumpin and touched that steel pole and squealed like a lil girl, But he sho nuff wore em after that.

[Mc Klien]

yeah. it sames that you test L1 and L2 are in 5 volts and the other has 120 volts. you know theirs something you for got. maybe you did not de-energized the other line. thats why you measured a 5 volts and 120 volts.Just check it again then try to measured in 3 or more times using digital and analog VOM. ok.