# Strange Voltages



## ExtinguishedSparky (Jun 22, 2021)

Single phase 3 wire 200 amp service. Everything seems normal. Properly bonded and grounded. But, L1 to neutral/gnd = 122.3 v, L2 to neutral/gnd = 122.9 v, and L1 to L2 = 241v. L1 carries about 1 amp more than L2 which shows up in the neutral like it should. Gnd carries no current.

What gives?


----------



## gpop (May 14, 2018)

power factor


----------



## ExtinguishedSparky (Jun 22, 2021)

Residential. Mostly resistive load. Maybe 1.5 hp at any given rime


----------



## paulengr (Oct 8, 2017)

Lots of loads these days are not resistive, even lighting.


----------



## splatz (May 23, 2015)

Is the service neutral reduced size? 

Did you measure voltage with the main open?


----------



## ExtinguishedSparky (Jun 22, 2021)

Is the service neutral reduced size? 
*Neutral is full sized on the customer side - can't speak for the powerco*
Did you measure voltage with the main open?
*Can't secure the whole service yet, but did secure all of the 240 v loads - same voltage disparity.*

What are you thinking? Seems if the neutral were open (or weak) on the powerco side then the L1-N and L2-N voltages would vary more with load and they don't seem to. When I secured all of the 240v loads the L1 and L2 currents were different by a factor of 2, which should have given vastly different L-N voltages, methinks.


----------



## SWDweller (Dec 9, 2020)

How much did you spend on your VOM and when was it last calibrated?


----------



## ExtinguishedSparky (Jun 22, 2021)

SWDweller said:


> How much did you spend on your VOM and when was it last calibrated?


Meter is a Fluke 323 at about $125. It was new about 4 months ago, so hasn't been calibrated.


----------



## splatz (May 23, 2015)

ExtinguishedSparky said:


> Is the service neutral reduced size?
> *Neutral is full sized on the customer side - can't speak for the powerco*
> What are you thinking? Seems if the neutral were open (or weak) on the powerco side then the L1-N and L2-N voltages would vary more with load and they don't seem to. When I secured all of the 240v loads the L1 and L2 currents were different by a factor of 2, which should have given vastly different L-N voltages, methinks.


With an open neutral, the 240/120 turns into a series / parallel 240VAC circuit and the voltage L1-N and L2-N will fluctuate - the bigger the disparity in load on L1 and L2, the bigger the disparity, but they'll still add up to 240. 

If the neutral return path is just higher resistance than normal (normal being just the resistance of the wire itself and good connections) it gets a little more complicated, more voltage drop in the wire, I can't quite connect the dots off the top of my head but it seems like you could wind up with unexpected voltages. It could be just where you were measuring on the neutral bar or where ever.


----------



## Slay301 (Apr 23, 2018)

I really don’t see what the problem is ? Maybe the house is the closest one to the transformer and the taps are set a tad high but even that’s a stretch. Also as more load is in the transformer the voltage will sag a bit. +or- 10%


----------



## ExtinguishedSparky (Jun 22, 2021)

splatz said:


> With an open neutral, the 240/120 turns into a series / parallel 240VAC circuit and the voltage L1-N and L2-N will fluctuate - the bigger the disparity in load on L1 and L2, the bigger the disparity, but they'll still add up to 240.
> 
> If the neutral return path is just higher resistance than normal (normal being just the resistance of the wire itself and good connections) it gets a little more complicated, more voltage drop in the wire, I can't quite connect the dots off the top of my head but it seems like you could wind up with unexpected voltages. It could be just where you were measuring on the neutral bar or where ever.


That's just it. The sum of the L1-N and L2-N voltages is greater than the L1-L2 voltage by 4 or 5 volts. And the L1-N and L2-N voltages don't vary given different loads. Can't come up with a way that explains all of this.


----------



## Slay301 (Apr 23, 2018)

ExtinguishedSparky said:


> That's just it. The sum of the L1-N and L2-N voltages is greater than the L1-L2 voltage by 4 or 5 volts. And the L1-N and L2-N voltages don't vary given different loads. Can't come up with a way that explains all of this.


It’s becuase your meter reads Volts RMS and this is an ac system Not dc so the sums won’t be exact


----------



## ExtinguishedSparky (Jun 22, 2021)

Slay301 said:


> It’s becuase your meter reads Volts RMS and this is an ac system Not dc so the sums won’t be exact


Been doing this for 50 years and never ran across a case where the sum of the L-N voltage exceeded the L-L.


----------



## Slay301 (Apr 23, 2018)

ExtinguishedSparky said:


> Been doing this for 50 years and never ran across a case where the sum of the L-N voltage exceeded the L-L.


If you were measure peak voltage assuming 0 voltage drop( L1to n) + (L2 to n) = L1+L2


----------



## SWDweller (Dec 9, 2020)

Flukes self test. You will get a screen that will let you know if there is a problem.

Was hoping it was something decent not some HF freeby give away.


----------



## ExtinguishedSparky (Jun 22, 2021)

SWDweller said:


> Flukes self test. You will get a screen that will let you know if there is a problem.
> 
> Was hoping it was something decent not some HF freeby give away.


Done that - no probs


----------



## cuba_pete (Dec 8, 2011)

ExtinguishedSparky said:


> Been doing this for 50 years and never ran across a case where the sum of the L-N voltage exceeded the L-L.


You've been doing this for _50 years_ and you _just _joined ET?

What did the sparkies at Tradeworks say?


----------



## ExtinguishedSparky (Jun 22, 2021)

cuba_pete said:


> You've been doing this for _50 years_ and you _just _joined ET?
> 
> What did the sparkies at Tradeworks say?


Never needed help before! (Ha!) Just discovered this site. 

Cut my teeth in Chicago in the 60s converting buildings form DC to AC. You know, back when we had to climb to the top of a ladder with a little dip pot full of solder to make up splices. You know, messing up nice strait pieces of pipe up with a chicago bender, putting double locknuts and bushings on heavywall in 1900, 8B and 11b boxes, making up panels with barbers twine and clove hitches. Most of my time on industrial jobs. Quite a bit of time on Power Plants - coal nuclear and hydro. I know that comes out to more than 50 years, but I always just round to half a century, doesn't make me seem so old.

Satisfied?


----------



## Slay301 (Apr 23, 2018)

ExtinguishedSparky said:


> Never needed help before! (Ha!) Just discovered this site.
> 
> Cut my teeth in Chicago in the 60s converting buildings form DC to AC. You know, back when we had to climb to the top of a ladder with a little dip pot full of solder to make up splices. You know, messing up nice strait pieces of pipe up with a chicago bender, putting double locknuts and bushings on heavywall in 1900, 8B and 11b boxes, making up panels with barbers twine and clove hitches. Most of my time on industrial jobs. Quite a bit of time on Power Plants - coal nuclear and hydro. I know that comes out to more than 50 years, but I always just round to half a century, doesn't make me seem so old.
> 
> Satisfied?


wait one more did they even have meters 50 years ago ?


----------



## gpop (May 14, 2018)

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.


----------



## ExtinguishedSparky (Jun 22, 2021)

Slay301 said:


> wait one more did they even have meters 50 years ago ?


Ya, had a triplet 631 - you know the kind with a vacuum tube on the input to raise the impedence on some ranges - weighed a ton and ate batteries. Still have it.


----------



## joe-nwt (Mar 28, 2019)

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


----------



## wiz1997 (Mar 30, 2021)

I'm with joe-nwt.
Read the OP several times and could not see what the problem is.
45 years of electrical experience and never questioned similar volt readings.


----------



## R777V (May 16, 2016)

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?


Sent from my iPhone using Tapatalk


----------



## Almost Retired (Sep 14, 2021)

gpop said:


> 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 ...


----------



## Almost Retired (Sep 14, 2021)

gpop said:


> 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?


----------



## wiz1997 (Mar 30, 2021)

Almost Retired said:


> i am curious .... its a center tap transformer right? ... how did you get one phase out of sync with the other?


Incoming power from power company.


----------



## Almost Retired (Sep 14, 2021)

wiz1997 said:


> Incoming power from power company.


I am wondering if i missed something in the earlier posts. Are we talking about standard residential 120/240 single phase ? or something else ?


----------



## gpop (May 14, 2018)

Almost Retired said:


> 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.


----------



## Almost Retired (Sep 14, 2021)

gpop said:


> 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 !!


----------



## paulengr (Oct 8, 2017)

gpop said:


> 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.









“Long’’ and “Short’’ Transmission Lines | Transmission Lines | Electronics Textbook


Read about “Long’’ and “Short’’ Transmission Lines (Transmission Lines) in our free Electronics Textbook




www.allaboutcircuits.com





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,


----------



## gpop (May 14, 2018)

paulengr said:


> 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 was referring more to tricking a cheap hand held voltmeter than a true a voltage shift that could be measured by a scope.


----------

