Troubleshooting problems in a 1950's house (long post sorry)

[zappy]

I finished this job about a month ago. I get a call back saying his front living room outlets aren't working. So I get there check a outlet with my knopp, nothing. Try my ticker it's saying there's voltage. So I'm thinking a loose neutral. So I check what the voltage is with my amprobe H-G it's 70 something volts on all four outlets in the room. I go and flip on the half hot switch 120v H-G now, on all four outlets in the room. Still no neutral. I find 30-35v on the ground wires. They just rapped the GRD wire around the NM clamp screw. I look in the sub-panel, There was one GRD wire from a newer romex landed on the neutral bar. All the old existing romex didn't have a GRD. I take it off and there's voltage on it. Can you trust DMM all the time? Because the light on my knopp is suppose to light at around fifty volts, and it didn't light. Is this some kind of ghost voltage my ticker and DMM are picking up? When I hold one lead between my fingers and one on the ground I get a voltage reading too. Anyway, I take apart the half hot outlet wires. There's two cables in the box, two blacks, two whites. One cable has 120v H-N good. OK the other cable just goes back to the switch. So I don't understand how this one switch is affecting the other three outlets So I turn the switch to the off position, wirenut the two blacks together, wirenut the two whites together. Everything works now. They just dont have a half hot anymore. It's funny cause I was there before, and all this stuff was working fine when I left. Looked around in the attic, to try and find why there could be 30 something volts on those outlets GRD's. Notice 2-screw NM clamps cranked down all the way, pinching the wires, but that wasn't it. Owner was just happy to have his outlets working. Would a GFCI trip if it sensed voltage on the EGC thats on it's screw? That house wiring is all screwed up, I turn of all the sub-panel breakers, the living room lights are still on. Someone J-boxed the feeder in the attic, and tapped of it for the lights:roll: Thank you for your help.

 

[gar]

100212-0831 EST

zappy:

You need to break your discussion into quite a few paragraphs.

I finished this job about a month ago. I get a call back saying his front living room outlets aren't working.

This above is very broad basic background. Not too important to the problem except to set the stage for what follows.

So I get there check a outlet with my knopp, nothing. Try my ticker it's saying there's voltage. So I'm thinking a loose neutral. So I check what the voltage is with my amprobe H-G it's 70 something volts on all four outlets in the room.

These are your first measurements.

I assume the H-G was at an outlet. I am not sure you meant H-G, but I will assume that is correct. Because this is an unexpected reading I would have connected to a good ground connection instead of the outlet EGC, possibly a metalic water pipe that is close by, kitchen or bathroom pipe. If still a bad reading measure to a screwdriver driven into the earth outside.

Three measurements can be made that will tell you a lot. Outside earth to the EGC, neutral, and hot at an outlet under question. The following assumes use of a high impedance voltmeter.

EGC to earth should be quite close to 0, probably less than 1 V. Neutral to earth maybe up to several volts depending upon load current. Hot to earth near its nominal value, 120.

There are conditions where earth and the neutral-EGC-GEC in the main panel may not have near zero voltage difference. But until there is some reason to believe otherwise make the assumption of 0. If there is a bad neutral from the pole to the main panel, then under unbalanced loads in the house there would be a voltage drop from the main panel GEC to earth because of at least some neutral current flowing thru the the grounding electrode and earth.

EGC and neutral should be connected together in the main panel and tied to earth. Assume these three are in fact connected together and the connection impedances are very low, like in the range 0.001 ohm. The impedance from the ground rod or water pipe to the earth will be much higher than 0.001 ohm, but the impedance from the main panel connection of the neutral, EGC, GEC should be low to the grounding electrode(s).

If at your problem outlet the EGC to earth is near 0 V, then the EGC is probably not open. If the neutral to earth is 50 V, then the neutral is open somewhere. Assuming the neutral at the outlet is floating and no other equipment is connected to this part of the neutral, then connect a 100 W bulb from neutral to the EGC. If the neutral to earth voltage drops to near 0 V, then you have an open neutral.

Next I will use the same basic paragraph but change the open from neutral to EGC.

If at your problem outlet the neutral to earth is near 0 V, then the neutral is probably not open. If the EGC to earth is 50 V, then the EGC is open somewhere. Assuming the EGC at the outlet is floating and no other equipment is connected to this part of the EGC, then connect a 100 W bulb from neutral to the EGC. If the EGC to earth voltage drops to near 0 V, then you have an open EGC.

Is this making sense?

.

 

[zappy]

100212-0831 EST

zappy:

You need to break your discussion into quite a few paragraphs.
This above is very broad basic background. Not too important to the problem except to set the stage for what follows.


These are your first measurements.

I assume the H-G was at an outlet. I am not sure you meant H-G, but I will assume that is correct. Because this is an unexpected reading I would have connected to a good ground connection instead of the outlet EGC, possibly a metalic water pipe that is close by, kitchen or bathroom pipe. If still a bad reading measure to a screwdriver driven into the earth outside.

Three measurements can be made that will tell you a lot. Outside earth to the EGC, neutral, and hot at an outlet under question. The following assumes use of a high impedance voltmeter.

EGC to earth should be quite close to 0, probably less than 1 V. Neutral to earth maybe up to several volts depending upon load current. Hot to earth near its nominal value, 120.

There are conditions where earth and the neutral-EGC-GEC in the main panel may not have near zero voltage difference. But until there is some reason to believe otherwise make the assumption of 0. If there is a bad neutral from the pole to the main panel, then under unbalanced loads in the house there would be a voltage drop from the main panel GEC to earth because of at least some neutral current flowing thru the the grounding electrode and earth.

EGC and neutral should be connected together in the main panel and tied to earth. Assume these three are in fact connected together and the connection impedances are very low, like in the range 0.001 ohm. The impedance from the ground rod or water pipe to the earth will be much higher than 0.001 ohm, but the impedance from the main panel connection of the neutral, EGC, GEC should be low to the grounding electrode(s).

If at your problem outlet the EGC to earth is near 0 V, then the EGC is probably not open. If the neutral to earth is 50 V, then the neutral is open somewhere. Assuming the neutral at the outlet is floating and no other equipment is connected to this part of the neutral, then connect a 100 W bulb from neutral to the EGC. If the neutral to earth voltage drops to near 0 V, then you have an open neutral.

Next I will use the same basic paragraph but change the open from neutral to EGC.

If at your problem outlet the neutral to earth is near 0 V, then the neutral is probably not open. If the EGC to earth is 50 V, then the EGC is open somewhere. Assuming the EGC at the outlet is floating and no other equipment is connected to this part of the EGC, then connect a 100 W bulb from neutral to the EGC. If the EGC to earth voltage drops to near 0 V, then you have an open EGC.

Is this making sense?

.

Yes I meant Hot to ground (H-G) How do I know if I have a high impedance voltmeter? So when you take these measurements, use the volts setting not the ohms? So jerry rig like a keyless, put a 100w. bulb in it, set my meter to volts, run a wire from the keyless hot screw to whatever I'm testing GRD, NEU. on the outlet in question. Then run a wire from the NEU screw on the keyless to a screwdriver in the ground outside? Then take a voltage reading by putting my leads on the hot and neutral screws on the keyless? I might do this at home and play around with this. Very interesting. I owe you one for taking the time to help me. Thank you.

 

[gar]

100212-2041 EST

zappy:

You have to teach me something. What is a keyless? Apparently it is a lamp socket. What else does keyless mean?

A digital meter, such as a Fluke 27 or 87, is a meter with good resolution and has a high input impedance. For the current purposes high input impedance means the input shunt resistance of the meter is 10 megohms, and a shunt capacitance of maybe 100 pfd. At 120 V 10 megohms draws 12 microamperes. At 60 Hz and 120 V 100 pfd has a capacitive reactance of about 26 megohms. The specifications that come with the meter should provide the input impedance information.

When you have a wire bundled with other wires, for example Romex with ground, then there is capacitance between pairs of wires. In Romex the ground wire is midway between hot and neutral. There is about 20 pfd per foot between hot and ground, and the same between neutral and ground. Somewhat less between hot and neutral.

Suppose the EGC wire is floating and the Romex is 100 ft long. Then the capacitance between hot and EGC is about 2000 pfd, and similarly between neutral and EGC. With the neutral actually connected to the transformer center tap, the hot wire to one hot side of the transformer, and the EGC connected directly to nothing, then a two capacitor voltage divider of 2000 pfd in series with 2000 pfd exists across the hot to neutral supply. If you had a meter with infinite input impedance connected from neutral to the EGC, then if hot is 120 V relative to neutral the voltage from EGC to neutral will be about 60 V. Your meter is not infinite imput impedance but rather 10 megohms and 100 pfd. This meter input impedance is in parallel the 2000 pfd capacitor from EGC to neutral. This lowers the voltage read. 2000 pfd is about 1.3 megohms at 60 Hz.

Put a 100 W incandescent lamp in parallel with the meter input. Cold this bulb is about 10 ohms. A voltage divider of 10/1,300,000 across 120 V is about 0.001*120 = 0.12 V. This is somewhat incorrect, but not by much, because I did not use vector math.

To do the tests I have been describing you use AC volts, not ohms. One place I may have mentioned using the ohmmeter. Ignore that for now.

I think for your first home experiments you should do measurements relative to a screwdriver in the earth near your grounding electrode. This is just for learning. On an actual job you would not do this unless there was an indication there were earthing or pole to main panel neutral problems.

By doing measurements relative to earth for learning purposes you should get some familiarity with what kind of readings to expect.

Initially you won't use the 100 W bulb to load down the input impedance of the meter. In other words the meter will be used in its high input impedance mode.

As you move around your house to different outlets you should only see a small voltage between earth and any EGC. The first place to test is the cabinet of the main panel. If this is not a small voltage, then you have problems to solve before doing anything else. Tonight from my 1" copper water pipe coming thru the basement floor to the main panel is about 0.002 V. If I was in the earth outside it might be 50 to 100 MV. Throughout my yard I generally have 30 to 100 MV, sometimes 200 MV, from stray currents that have nothing to do with my transformer.

From my water pipe entry point to my shop bench, about 45 ft and maybe 70 ft of EGC wire and power wires, the following results occur:
No load on the bench --- EGC 3MV, neutral 4 MV.
With a computer and laser printer powered --- EGC 16 MV, neutral every where from 50 MV to something over 1 V depending upon what the laser printer heater is doing.

I do not need to use the light bulb for loading here because the circuit wiring has no bad connections.

If you have a 100 or 250 ft roll of romex, then strip the three wires at one end and make sure there is no short at the other end. Connect hot and neutral to power and let the EGC wire float. With the high impedance meter measure the voltage from EGC to neutral. What do you read. Now put the 100 W bulb in parallel with the two meter leads. Now what is the reading?

.

 

[zappy]

100212-2041 EST

zappy:

You have to teach me something. What is a keyless? Apparently it is a lamp socket. What else does keyless mean?

A digital meter, such as a Fluke 27 or 87, is a meter with good resolution and has a high input impedance. For the current purposes high input impedance means the input shunt resistance of the meter is 10 megohms, and a shunt capacitance of maybe 100 pfd. At 120 V 10 megohms draws 12 microamperes. At 60 Hz and 120 V 100 pfd has a capacitive reactance of about 26 megohms. The specifications that come with the meter should provide the input impedance information.

When you have a wire bundled with other wires, for example Romex with ground, then there is capacitance between pairs of wires. In Romex the ground wire is midway between hot and neutral. There is about 20 pfd per foot between hot and ground, and the same between neutral and ground. Somewhat less between hot and neutral.

Suppose the EGC wire is floating and the Romex is 100 ft long. Then the capacitance between hot and EGC is about 2000 pfd, and similarly between neutral and EGC. With the neutral actually connected to the transformer center tap, the hot wire to one hot side of the transformer, and the EGC connected directly to nothing, then a two capacitor voltage divider of 2000 pfd in series with 2000 pfd exists across the hot to neutral supply. If you had a meter with infinite input impedance connected from neutral to the EGC, then if hot is 120 V relative to neutral the voltage from EGC to neutral will be about 60 V. Your meter is not infinite imput impedance but rather 10 megohms and 100 pfd. This meter input impedance is in parallel the 2000 pfd capacitor from EGC to neutral. This lowers the voltage read. 2000 pfd is about 1.3 megohms at 60 Hz.

Put a 100 W incandescent lamp in parallel with the meter input. Cold this bulb is about 10 ohms. A voltage divider of 10/1,300,000 across 120 V is about 0.001*120 = 0.12 V. This is somewhat incorrect, but not by much, because I did not use vector math.

To do the tests I have been describing you use AC volts, not ohms. One place I may have mentioned using the ohmmeter. Ignore that for now.

I think for your first home experiments you should do measurements relative to a screwdriver in the earth near your grounding electrode. This is just for learning. On an actual job you would not do this unless there was an indication there were earthing or pole to main panel neutral problems.

By doing measurements relative to earth for learning purposes you should get some familiarity with what kind of readings to expect.

Initially you won't use the 100 W bulb to load down the input impedance of the meter. In other words the meter will be used in its high input impedance mode.

As you move around your house to different outlets you should only see a small voltage between earth and any EGC. The first place to test is the cabinet of the main panel. If this is not a small voltage, then you have problems to solve before doing anything else. Tonight from my 1" copper water pipe coming thru the basement floor to the main panel is about 0.002 V. If I was in the earth outside it might be 50 to 100 MV. Throughout my yard I generally have 30 to 100 MV, sometimes 200 MV, from stray currents that have nothing to do with my transformer.

From my water pipe entry point to my shop bench, about 45 ft and maybe 70 ft of EGC wire and power wires, the following results occur:
No load on the bench --- EGC 3MV, neutral 4 MV.
With a computer and laser printer powered --- EGC 16 MV, neutral every where from 50 MV to something over 1 V depending upon what the laser printer heater is doing.

I do not need to use the light bulb for loading here because the circuit wiring has no bad connections.

If you have a 100 or 250 ft roll of romex, then strip the three wires at one end and make sure there is no short at the other end. Connect hot and neutral to power and let the EGC wire float. With the high impedance meter measure the voltage from EGC to neutral. What do you read. Now put the 100 W bulb in parallel with the two meter leads. Now what is the reading?

.

A "keyless" is a porcelain light fixture. You see them in attics usually. I don't think I have a high impedance meter. Mine is a amprobe ACD-10 TRMS. Digital clamp-on volt/amp/ohmmeter. So using a "wiggy" wont always tell you there is a problem with a circuit? You should always hook at least a 100w load to it to make sure? So if there is a problem with the circuit, the bulb will be dim? When I set my meter to ohms, and hook it up to a long piece of wire, it just rings and says O.L I never use the ohms setting, except for a continuity test. I don't understand how to use my meter for reading ohms. Maybe you can explain? Oh and some of the stuff you were saying went WAY over my head. But thank you anyway. If I keep trying all get it. There's alot of satisfaction being a electrician. I'm never bored, there's always more to know!

 

[gar]

100213-0802 EST

zappy:

Here is the spec sheet for your meter.
http://www.amprobe.com/specsheets/ACDC100.pdf
Maybe it is not your meter. I do not get ACDC-10 at the Amprobe site. Only the ACDC-100.
From the specs the ACDC-100 looks like a very useful meter. It is a 10 megohm input impedance meter on the volt ranges. Your meter will resolve 0.1 MV. On resistance the smallest increment is 0.1 ohm.

Find a 250 ft or more roll of #16 wire. #16 is 4.016 ohms per 1000 ft. Strip the two ends of the coil of wire and measure with your ohmmeter and calculate the length of wire on the spool.

You appear to be a person interested in learning. Start experimenting as I described above and see what your results are and continue to ask questions.

.

 

[zappy]

100213-0802 EST

zappy:

Here is the spec sheet for your meter.
http://www.amprobe.com/specsheets/ACDC100.pdf
Maybe it is not your meter. I do not get ACDC-10 at the Amprobe site. Only the ACDC-100.
From the specs the ACDC-100 looks like a very useful meter. It is a 10 megohm input impedance meter on the volt ranges. Your meter will resolve 0.1 MV. On resistance the smallest increment is 0.1 ohm.

Find a 250 ft or more roll of #16 wire. #16 is 4.016 ohms per 1000 ft. Strip the two ends of the coil of wire and measure with your ohmmeter and calculate the length of wire on the spool.

You appear to be a person interested in learning. Start experimenting as I described above and see what your results are and continue to ask questions.

.

My meter is from the 90's. It's old. They might not even make it anymore. But I have the directions to mine. Maybe I can read you the specs. and you can tell me what I can and cant do with it? Here's what it says about Ohms: 0-4Kohms, Resolution 1ohm. 0-40K ohms, Resolution 10ohms. Accuracy 1.9% of rdg. + 8 LSD

 

[gar]

100213-1303 EST

zappy:

Your meter has less capability on resistance than the ACDC-100. The smallest increment your meter can read in resistance is 1 ohm in comparison with the -100 that can resolve 0.1 ohm.

This also may mean on the voltage range your lower resolution might be 0.001 V or 1 MV.

In particular the accuracy part of the ohms spec means this:
"Accuracy 1.9% of rdg. + 8 LSD "
On the 0 to 4000 ohm range which reads 0, 1, 2, 3, .... 4000 the reading could be in error by +/-1.9% of the reading and in addition to that error 8 LSD (for this range 8 LSD = 8 ohms). LSD represents Least Significant Digit. So a reading of 0 could be anything from 0 to 8 ohms. A reading of 2000 ohms could be anything from 2000 +/-(2000*.019 +8) = 2000 +/-(38+8) = 2000 +/-46 ohms. At 4000 ohms it becomes 4000 +/-84 ohms.

.

 

[gadfly56]

See here for the spec sheet on your meter. By the way, there's a safety recall on it. See here.

 

[gar]

100216-1955 EST

zappy:

The spec sheet provided by gadfly56 does indicate a very capable instrument. It resolves 0.1 MV and 0.1 ohm.

Have you started to do some of the experiments that we have discussed?

.

 

[dbuckley]

Point 1 of a megavolt??? - thats one damned scary measuring tool

 

[mivey]

Point 1 of a megavolt??? - thats one damned scary measuring tool

So it is good for measuring 100 GW.

 

[gar]

100216-2150 EST

In my typical measurement area MV is an abbreviation for millivolt. But in other areas its good for megavolt. So we have a 10^9 error. I also like KC for kilocycles and MC for megacycle. They are fading, and I have come around to those Hertz things. 1 M was a 1000 ohms while 1 Meg was 10^6 ohms. But the evolution to 1 K and 1 M is more useful. And we had mmfd instead of pfd. In some older days it was hard to find any signal much above a few hundred MC (mHz).

.

 

[zappy]

See here for the spec sheet on your meter. By the way, there's a safety recall on it. See here.

Thank you Gadfly! Good lookin out!

 

[zappy]

100216-1955 EST

zappy:

The spec sheet provided by gadfly56 does indicate a very capable instrument. It resolves 0.1 MV and 0.1 ohm.

Have you started to do some of the experiments that we have discussed?

.

Thank you for asking. No not yet, but soon.

 

[zappy]

Gar, since my meter has been recalled. They have given me a choice between, the Amprobe ACD-10 TRMS Plus or the ACD-14 TRMS-FX. Which one is better? I'm guessing based on the price, the ACD-14 TRMS-FX model. Thank you.