Phase Identification

In a three phase system three wires are of colour red, yellow and blue are used to discriminate each phase. Now how will you identify each phase wire without knowing the colour and without any pre information?

Questions by elexengg

Showing Answers 1 - 10 of 10 Answers

For this a known 3-phase source is required. Phasing out between your unidentified 3-phase system with known system , you can identify the R , Y & B PHASES.

           Known System              Unknown System

               R                                     r               = 0.00 V
               Y                                     r               = 110 V
               B                                    r                = 110 V

              R                                   y                =110 V
              Y                                   y                = 0.00 V
              B                                  y                 = 110 V

               R                                    b               = 110 V
               Y                                    b              =   110 V
               B                                    b               = 0.00 V


  • Mar 6th, 2011

If I understand what you're asking about, there are devices available that use GPS clocks to identify an unknown voltage phase. 

They work by comparing zero-crossing times between two locations. The reference unit is installed on a Phase "A" voltage and by measuring the zero-crossing time at the location of an unknown phase in comparison to the known reference phase, the unknown phase identification can be determined. See for one example device.

This device functions based on the fact that the electric grid is basically in phase across 100's of miles of distance. 

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  • Jun 29th, 2014

when there no color code how to know r y b and how to test it

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Walt Slade

  • Jun 30th, 2014

As I said above, there are devices that use a reference and GPS clocks. For example the EDM AP-30 can be touched onto an energized, unlabelled wire and it will display the degrees leading/lagging from the reference. In the US, the standard phase A is at zero degrees, B is at -120 and C is at +120. The AP-30 will display the angle for each unknown conductor. That gives the identification, angle and rotation.

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  • Jun 5th, 2017

If I don't have any meter than what will I do?

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  • Jun 7th, 2017

If you dont have a device like the GPS-based phase I.D. one mentioned above, you basically need to visually trace the wires, starting from a known phase I.D. location, or use an Ohmmeter type device on a de-energized wire and short out one at a time. This can be dangerous. See for info on GPS-based device.

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  • Nov 21st, 2017

How to identify the neutral wire on distribution pole physically with out any test conducted

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  • Nov 22nd, 2017

The neutral is often at the very top of a pole or it could be below the three hot phases. If all the wires are side by side, it sometimes uses a smaller insulator because theres very little voltage on the neutral. If all the insulators are the same size and the wires are side by side, some utilities put an "N" tag on the crossarm next to that wire.

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Soumya Ranjan Nayak

  • Dec 28th, 2017

Go for continuity test from source end & at testing end test in discharge condition.

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