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I wouldn't even bat an eye at voltage readings like that because a simple VOM doesn't tell the whole story.
 

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Wow, seriously you are sweating a voltage difference like that? I also concur, that’s nothing, again it comes down to what meter you are using, was it and when was it calibrated? Meters reading average won’t probably be exact, I mean subtracting the decimals is it off that much? I would be more inclined to worry if you were checking with a 1000$ dollar recently calibrated meter, not a sub 200$ meter. Also how is the power quality in the area, is it near any industrial, what time of day, what was the weather like etc?


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If you have 2 sine waves 180 degrees out of sync then shift one forwards or backwards a tiny amount then adding L1 to N + L2 to N will not equal L1 + L2.

You could try removing all the loads then testing to see if you can get it closer.
I suggest that you may have some non-linear loads. ie power supplies. they produce prodigious harmonics and are the reason the code is considering requiring that 12-2G romex have oversized neutrals. you cant see it without an oscilloscope but it will overload a nearly loaded neutral at 120V. Just guessing ...
 

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If you have 2 sine waves 180 degrees out of sync then shift one forwards or backwards a tiny amount then adding L1 to N + L2 to N will not equal L1 + L2.

You could try removing all the loads then testing to see if you can get it closer.
i am curious .... its a center tap transformer right? ... how did you get one phase out of sync with the other?
 

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i am curious .... its a center tap transformer right? ... how did you get one phase out of sync with the other?
At the transformer the waves would be in sync as you go further down the line you can cause the peak of one wave to lead or lag. As a volt meter is sampling thousands of times a second looking for peak voltage before converting the reading to rms it only requires a tiny shift of the peak to trick the meter into thinking the rms wave have shifted. Higher quality meters sample faster and are better at making the conversion to rms which is why some meters get stupid on pwm signals.
In this case you are only looking for a tiny amount of perceived shift which could be a capacitor wave clipping (charging at peak voltage) between L1 or L2 and N. The meter will still read peak to N as full voltage but when you sample L1 to L2 the timing will make it look like one peaked before the other so it will report a lower voltage. Unequal length feeders can also cause this affect but it's less likely in residential.
 

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At the transformer the waves would be in sync as you go further down the line you can cause the peak of one wave to lead or lag. As a volt meter is sampling thousands of times a second looking for peak voltage before converting the reading to rms it only requires a tiny shift of the peak to trick the meter into thinking the rms wave have shifted. Higher quality meters sample faster and are better at making the conversion to rms which is why some meters get stupid on pwm signals.
In this case you are only looking for a tiny amount of perceived shift which could be a capacitor wave clipping (charging at peak voltage) between L1 or L2 and N. The meter will still read peak to N as full voltage but when you sample L1 to L2 the timing will make it look like one peaked before the other so it will report a lower voltage. Unequal length feeders can also cause this affect but it's less likely in residential.
That makes sense now. initially i was thinking no way. Thank you !!
 

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Chief Flunky
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At the transformer the waves would be in sync as you go further down the line you can cause the peak of one wave to lead or lag. As a volt meter is sampling thousands of times a second looking for peak voltage before converting the reading to rms it only requires a tiny shift of the peak to trick the meter into thinking the rms wave have shifted. Higher quality meters sample faster and are better at making the conversion to rms which is why some meters get stupid on pwm signals.
In this case you are only looking for a tiny amount of perceived shift which could be a capacitor wave clipping (charging at peak voltage) between L1 or L2 and N. The meter will still read peak to N as full voltage but when you sample L1 to L2 the timing will make it look like one peaked before the other so it will report a lower voltage. Unequal length feeders can also cause this affect but it's less likely in residential.
You are thinking of CURRENT, not voltage.

Voltage will lead/lag because of line lengths and propagation delays. But you are talking about a very long cable, much longer than any distribution system, even in mountainous areas.


I mean propagation delays are a real “thing”. In the early Cray supercomputers they purposely built it with different length wires so all the signals arrived with the right timing. You get about 100 picoseconds per inch.

CURRENT on the other hand leads/lags easily. A motor starting draws current almost a full 90 degrees lagging,
 

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You are thinking of CURRENT, not voltage.

Voltage will lead/lag because of line lengths and propagation delays. But you are talking about a very long cable, much longer than any distribution system, even in mountainous areas.


I mean propagation delays are a real “thing”. In the early Cray supercomputers they purposely built it with different length wires so all the signals arrived with the right timing. You get about 100 picoseconds per inch.

CURRENT on the other hand leads/lags easily. A motor starting draws current almost a full 90 degrees lagging,
I was referring more to tricking a cheap hand held voltmeter than a true a voltage shift that could be measured by a scope.
 
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