Buck Parrish
Senior Member
- Location
- NC & IN
I did, but it doesn't compute.
Or I should have said call a service and repair electrician.:smile:
Help! Lights flickering in 3 story home.
- Thread starter ndpelectric
- Start date
- Status
I did, but it doesn't compute.
Or I should have said call a service and repair electrician.:smile:ndpelectric
Member
I took my amp clamp to a neutral of a circuit drawing 3.5 amps, and the neutral had the same amount of amperage.
This means there is any open neutral.
But in a house were nothing has been touched in years, how is this possible.
This means there is any open neutral.
But in a house were nothing has been touched in years, how is this possible.
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
Who says that means there is an open neutral??
-Hal
-Hal
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
I think they meant to say the hot and neutral had the same amount of current, that there was not an open neutral. Still not proof either way though.
ptonsparky
Tom
- Occupation
- EC - retired
If you have an overhead service to the house look @ all the connections from transformer to panels. While you are looking, you just as well take them all apart, clean and torque. Pay particular attention to the PP neutral connection that has failed. Maybe more than one connection depending on the length & makeup of the service.
Undergound, look at connections where visible. Have the POCO disconnect their end so you can test the underground for faults. A megger is best, but a good VOM can get you pointed in the right direction. Handheld testers such as the Fluke Pro are usually worthless for checking undergound.
Underground faults can be located with the right equipment. Where did you say you are located? Hint Hint.
Undergound, look at connections where visible. Have the POCO disconnect their end so you can test the underground for faults. A megger is best, but a good VOM can get you pointed in the right direction. Handheld testers such as the Fluke Pro are usually worthless for checking undergound.
Underground faults can be located with the right equipment. Where did you say you are located?
Hint Hint.gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
081217-0725 EST
ndpelectric:
I think you are failing to understand the logic of the circuit you are trying to troubleshoot.
1st. You have a power company supply transformer somewhere close to the house, maybe 500 ft away, but unlikely that far. Probably not closer than 50 ft.
2nd. That transformer has a center tapped secondary that provides a nominal 120-0-120 output. A wire connected to the center tap and run to the house is called neutral.
3rd. In this discussion ignore the KWH meter and just assume that wires run from the transformer to the main panel.
4th. At the transformer there is a second wire that runs from the center tap down the pole and connects to a power company ground rod that is driven into the ground at the pole. This wire is called a GEC (ground electrode conductor) because it is a conductor from something (the transformer neutral) to a ground electrode (ground rod). Ideally under normal conditions no current or little flows in this GEC.
5th. There are two 120 V, relative to neutral, hot wires from the transformer to the main panel. These are 180 deg out of phase with each other relative to the neutral.
6th. At the main panel there is a neutral bus and a ground bus and the two are connected together at the panel (bonded). All the safety ground wires (green or bare) EGC (equipment grounding conductors) of the entire house are terminated on the ground bus.
7th. All neutral wires in the house are terminated on the neutral bus. There should be no voltage difference between the neutral bus and the ground bus because these are connected together.
8th. Also terminated on the ground bus is another GEC that connects to a grounding electrode at, near, the service entrance. This ground electrode may be a ground rod, a copper water line, or items that serve the same purpose, or a combination of these. At the time of installation the current code would have determined what was required.
9th. The neutral wire from the transformer to the main panel is of relatively low resistance. If it were 100 ft of 00 copper its resistance would be 0.008 ohms. 100 A thru this would produce a voltage drop of 0.8 V.
10th. By contrast a path thru the earth between the two ground rods might be 10 ohms, probably low for most locations.
11th. Using these values the expected current thru the earth would be about 1/1000 the current thru the neutral conductor, for the 100 A neutral case about 100 MA (0.1 A).
There are other paths that may appear to be thru the earth but are really thru water lines between houses and other neutrals.
Your following statement:
You expect the current on the branch circuit neutral to equal the current in the hot wire of that circuit. In fact put a clamp on ammeter with MA capability around both the branch circuit neutral and the hot wire, but not the EGC (ground wire), and the current reading should be 0 even with a 100 A load. This is a more accurate measure that the two currents are equal and that there is no leakage somewhere around the load.
Do this: Be careful with this test to avoid a shock. Use a high impedance voltmeter. For example a Fluke 27. Measure the voltage from a point in the yard closest to the pole transformer ground rod and to a point close to the house where the main panel is located. The pole transformer may be a number of backyards away. Therefore pick the corner of your yard closest to that transformer. The goal of this test is to see if there is substantial current flowing in the earth because of an open or high resistance neutral wire from the transformer to the main panel. Do this with all loads turned off in the house. Should be near 0 V. Then with a large load on one side of neutral. For the load this means something like a 120 V 1500 W heater as the only load, about 12 A. If this voltage is greater than 1 V when the load is on, then there is a neutral problem between the pole transformer center tap and the main panel.
.
ndpelectric:
I think you are failing to understand the logic of the circuit you are trying to troubleshoot.
1st. You have a power company supply transformer somewhere close to the house, maybe 500 ft away, but unlikely that far. Probably not closer than 50 ft.
2nd. That transformer has a center tapped secondary that provides a nominal 120-0-120 output. A wire connected to the center tap and run to the house is called neutral.
3rd. In this discussion ignore the KWH meter and just assume that wires run from the transformer to the main panel.
4th. At the transformer there is a second wire that runs from the center tap down the pole and connects to a power company ground rod that is driven into the ground at the pole. This wire is called a GEC (ground electrode conductor) because it is a conductor from something (the transformer neutral) to a ground electrode (ground rod). Ideally under normal conditions no current or little flows in this GEC.
5th. There are two 120 V, relative to neutral, hot wires from the transformer to the main panel. These are 180 deg out of phase with each other relative to the neutral.
6th. At the main panel there is a neutral bus and a ground bus and the two are connected together at the panel (bonded). All the safety ground wires (green or bare) EGC (equipment grounding conductors) of the entire house are terminated on the ground bus.
7th. All neutral wires in the house are terminated on the neutral bus. There should be no voltage difference between the neutral bus and the ground bus because these are connected together.
8th. Also terminated on the ground bus is another GEC that connects to a grounding electrode at, near, the service entrance. This ground electrode may be a ground rod, a copper water line, or items that serve the same purpose, or a combination of these. At the time of installation the current code would have determined what was required.
9th. The neutral wire from the transformer to the main panel is of relatively low resistance. If it were 100 ft of 00 copper its resistance would be 0.008 ohms. 100 A thru this would produce a voltage drop of 0.8 V.
10th. By contrast a path thru the earth between the two ground rods might be 10 ohms, probably low for most locations.
11th. Using these values the expected current thru the earth would be about 1/1000 the current thru the neutral conductor, for the 100 A neutral case about 100 MA (0.1 A).
There are other paths that may appear to be thru the earth but are really thru water lines between houses and other neutrals.
Your following statement:
Does not provide any information on whether or not there is an open or loose neutral between the main panel and the transformer center tap.
You expect the current on the branch circuit neutral to equal the current in the hot wire of that circuit. In fact put a clamp on ammeter with MA capability around both the branch circuit neutral and the hot wire, but not the EGC (ground wire), and the current reading should be 0 even with a 100 A load. This is a more accurate measure that the two currents are equal and that there is no leakage somewhere around the load.
Do this: Be careful with this test to avoid a shock. Use a high impedance voltmeter. For example a Fluke 27. Measure the voltage from a point in the yard closest to the pole transformer ground rod and to a point close to the house where the main panel is located. The pole transformer may be a number of backyards away. Therefore pick the corner of your yard closest to that transformer. The goal of this test is to see if there is substantial current flowing in the earth because of an open or high resistance neutral wire from the transformer to the main panel. Do this with all loads turned off in the house. Should be near 0 V. Then with a large load on one side of neutral. For the load this means something like a 120 V 1500 W heater as the only load, about 12 A. If this voltage is greater than 1 V when the load is on, then there is a neutral problem between the pole transformer center tap and the main panel.
.
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