120-220 Volt single phase service, possible? (Brooklyn Gowanus neighborhood).

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victor.cherkashi

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I did a field survey today in two family house (Brooklyn Gowanus neighborhood). Owner called electrical, he said that house have 120/220 service. I did not believe him so I measured by myself, see attached picture.



White – red/white = 118V

White – black/white = 117V

Red/white – black/white = 217V



What type of system is that? Type of service transformer?
 

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victor.cherkashi said:
I did a field survey today in two family house (Brooklyn Gowanus neighborhood). Owner called electrical, he said that house have 120/220 service. I did not believe him so I measured by myself, see attached picture.



White – red/white = 118V

White – black/white = 117V

Red/white – black/white = 217V



What type of system is that? Type of service transformer?
Click to expand...
When I was in school 50 plus years ago they called it a 3 wire Edison system. The center point of the utility companies 240 volt secondary has a center tap connection providing now what is called the grounded conductor ( white neutral wire ) . An example is you could have 235 volts between the two energized wires resulting in 115 volts from first energized wire and 120 volts on the other. Very seldom do the two legs to the white neutral have the same exact voltage. Have seen differences of over 12 volts especially in old homes that have say maybe 75% or more of total load on one side of single phase 3 wire services. Hope this helps.
 
garbo said:
An example is you could have 235 volts between the two energized wires resulting in 115 volts from first energized wire and 120 volts on the other. Very seldom do the two legs to the white neutral have the same exact voltage.
Click to expand...
I'm thinking the difference between his 217v and my 235v is his point, not the 1v difference between lines.

However, I'm a little puzzled that the two L-N voltages are less than 120v, yet the L-L voltage exceeds 208v.
 
The voltage readings are indeterminate.

My guess is that this is a 120/208 two legs tapped from three phase service, with voltage heavily corrupted by harmonics.

The utility meters say FM12S on the label, which is generally used for 120/208

Jon
 
Agree with others. 12S &25S meters are five terminal meters generally reserved for network metering.
118 X 1.732 = 204…
I’m kinda in agreement with Winnie on this one..
It’s almost like everything in the house is powered from rectified DC and flat topping the waveform
 
I agree that a likely cause for the voltage discrepancy is harmonic distortion of 120/208 service voltages.

With sinusoidal voltage waveforms the L1-N and L2-N voltages would have to be at 135° apart from each other instead of the nominal 120° to get the measurements above. That could happen if there was a large voltage drop on the service neutral wire.
For example, the 208/120 service voltage could be 4.3% high to give the measured 217V L-L. But a 17.5 V drop on the service neutral coming from balanced L-L loads would make the L-N voltages around 117.5V instead of the 1.043 x 120V = 125.2V with no drop. That would be a lot of voltage drop which is unlikely, but it could still be checked in order to rule it out.
 
victor.cherkashi said:
I did a field survey today in two family house (Brooklyn Gowanus neighborhood). Owner called electrical, he said that house have 120/220 service. I did not believe him so I measured by myself, see attached picture.



White – red/white = 118V

White – black/white = 117V

Red/white – black/white = 217V



What type of system is that? Type of service transformer?
Click to expand...
ConEd pretty much only supplies 3PH 208/120V services in the 5 boroughs. Once you get to westchester or that area, you may get away with them giving you 480/277.

Given that this looks to be a building with multiple units and knowing the power company and the area, I would agree with everyone else that it is two phases of a 208/120V three phase service.

The splitting up of the 208/120V three phase service to feed separate condos, apartments, etc is popular and has been discussed in this forum previously with some great info on it.
 
The multimeter I used has no label "true RMS", I think it could be a reason for corrupted measurement when harmonics are present. Do you believe a multimeter with "true RMS" label give much better results?
 
spraymax6 said:
ConEd pretty much only supplies 3PH 208/120V services in the 5 boroughs. Once you get to westchester or that area, you may get away with them giving you 480/277.
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100% agree with Spraymax6 here. My family home back in Brooklyn (Midwood section of Flatbush) was one of many single family residences fed 2 phases of an underground ConEd 208Y/120 4W secondary. So "technically" I think you'd label it 120/208?

This really confused me when I was a kid - many years ago. All the early books I was reading to learn about wiring never mentioned 3 phase power and the "math" behind the voltages. So I could not understand why I was not reading 240V L-L on my trusty Army surplus VOM.

But anyway - very likely 2 hots from a 3 phase ConEd feed. Come back at 3PM on a hot August day and I bet that 217V is a lot closer (if not under) to 208V.
 
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