Electrical Voltage testing

[brother]

This reminds of the thread, voltage (or current) returning to a 'different' source. Looking at mike holts pics from the illustrated guide to understanding the NEC Vol 1 page 417 talking about voltage between adjacent devices, you have one with the 277 120 switches.

But i thought about it for a second, and if you actually used your meter in real life, you would not read a voltage between the 2 switches because the voltage come from a different source. Basically you would not have a voltage between the devices of '381'. Has anyone ever actually tried it out??

Now the 277 to 277 you would get over 300volts (a violation) basically getting 480.

 

[infinity]

The graphic is correct. That scenario does exist in the real world. This subject came up a while ago and some of the engineer's here performed a lengthy calculation to prove the existence of 381 volts between the two devices. Maybe one of them will chime in.

 

[roger]

But i thought about it for a second, and if you actually used your meter in real life, you would not read a voltage between the 2 switches because the voltage come from a different source. Basically you would not have a voltage between the devices of '381'. Has anyone ever actually tried it out??

Absolutely you would, next time you have a 480 to 208Y/120 v transformer open try it yourself and log your readings for each combination read.

Roger

 

[mivey]

The last time I looked I got:

With a wye-wye and no phase shift it would be 157.1 from phase a to a'. It would be 352.8 from a to b' or c'.

With a delta-wye and 30 degree phase shift, it would be 183.3 from a to a'. It would be 385.7 from a to b'. It would be 302.0 from a to c'.

 

[LarryFine]

As long as the two sources have any conductor in common, which they will if they're both grounded, there will be voltages among all conductors.

Imagine the maximum voltage between a conductor of a corner-grounded primary and one of a corner-grounded secondary.