gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
090427-0818 EST
I would like to get experimental data from anyone willing to run the experiment.
The experiment is as follows:
1. Residential 50 to 200 A service with 240/120 transformer. In other words has a neutral (a center tapped transformer secondary).
2. Test load about 12 A at 120 V (a typical 1500 W heater).
3. A digital meter capable of resolving 0.1 V on a range that includes 120 V capability.
4. Classify one phase as A and the opposite one as B.
5. Pick any outlet for phase A.
6. Connect the meter to this phase A outlet.
7. Measure and record the voltage with and without the test load plugged into this same outlet. Implication is that this is a duplex so that we are not measuring the load caused voltage drop across the load 's plug. This does measure all voltage drops starting at the transformer and including the rear connections to the duplex outlet.
8. Find a different phase A outlet that is not on the same breaker as the outlet in (7). Measure the voltage at this second phase A outlet with and without the test load connected to its outlet of (7). What this test does is essentially measure the phase A voltage at the main panel with and without the load connected to phase A. In other words all the drops from the transformer to the main panel.
9. Last find a phase B circuit and connect the voltmeter to it. Then do the same as in (8).
10. If possible record the pole transformer size, wire size, kind (Al or Cu), and length from transformer to meter.
What do I expect:
In experiment 9 the reading should not change or it should increase with the load connected. At my home I get between 0 and 0.1 V increase. At two other homes I got 3.5 V, and 1.4 V. These seem high to me. The transformer to main panel wire length is about 70 ft in both cases.
In experiments 7 and 8 I expect the voltage to drop, and experiment 8 should drop less than experiment 7. In my home and experiment 7 and an outlet very close to the main panel I get a 1.1 V drop. Exp 8 produces 0.6 to 0.7 V drop.
The voltage drop in experiment 9 provides a measure of the resistance of the neutral path. So for for my home it is less than 0.1/12 = 0.008 ohms. For my home transformer impedance, wire resistance, meter, and fuse resistances total about 0.7/12 = 0.058 ohms and subtracting the neutral path produces 0.050 for the hot path.
In both of the other homes the total wire length from the transformer to the main panel was about 70 ft. Based on this length I believe the neutral drops are too high. So is there something wrong with the design of my experiment or are there some high resistance connections on the neutrals of these two other locations?
I believe my experimental method is a useful tool for troubleshooting supply problems. Data from anyone else and thus different locations can be useful in determining the effectiveness of this approach.
.
I would like to get experimental data from anyone willing to run the experiment.
The experiment is as follows:
1. Residential 50 to 200 A service with 240/120 transformer. In other words has a neutral (a center tapped transformer secondary).
2. Test load about 12 A at 120 V (a typical 1500 W heater).
3. A digital meter capable of resolving 0.1 V on a range that includes 120 V capability.
4. Classify one phase as A and the opposite one as B.
5. Pick any outlet for phase A.
6. Connect the meter to this phase A outlet.
7. Measure and record the voltage with and without the test load plugged into this same outlet. Implication is that this is a duplex so that we are not measuring the load caused voltage drop across the load 's plug. This does measure all voltage drops starting at the transformer and including the rear connections to the duplex outlet.
8. Find a different phase A outlet that is not on the same breaker as the outlet in (7). Measure the voltage at this second phase A outlet with and without the test load connected to its outlet of (7). What this test does is essentially measure the phase A voltage at the main panel with and without the load connected to phase A. In other words all the drops from the transformer to the main panel.
9. Last find a phase B circuit and connect the voltmeter to it. Then do the same as in (8).
10. If possible record the pole transformer size, wire size, kind (Al or Cu), and length from transformer to meter.
What do I expect:
In experiment 9 the reading should not change or it should increase with the load connected. At my home I get between 0 and 0.1 V increase. At two other homes I got 3.5 V, and 1.4 V. These seem high to me. The transformer to main panel wire length is about 70 ft in both cases.
In experiments 7 and 8 I expect the voltage to drop, and experiment 8 should drop less than experiment 7. In my home and experiment 7 and an outlet very close to the main panel I get a 1.1 V drop. Exp 8 produces 0.6 to 0.7 V drop.
The voltage drop in experiment 9 provides a measure of the resistance of the neutral path. So for for my home it is less than 0.1/12 = 0.008 ohms. For my home transformer impedance, wire resistance, meter, and fuse resistances total about 0.7/12 = 0.058 ohms and subtracting the neutral path produces 0.050 for the hot path.
In both of the other homes the total wire length from the transformer to the main panel was about 70 ft. Based on this length I believe the neutral drops are too high. So is there something wrong with the design of my experiment or are there some high resistance connections on the neutrals of these two other locations?
I believe my experimental method is a useful tool for troubleshooting supply problems. Data from anyone else and thus different locations can be useful in determining the effectiveness of this approach.
.
The neutral currents should have been shown as: