ECN Forum Forums General Topics of the Trade General Discussion Area voltage readings

This question is in reference to switches when permanent dividers are needed when the voltage between switches exceeds 300 volts.

The book I have shows the voltage between 120 switch and a 277 volts switch to be 380 volts. How is this figure obtained? How can there be a potential difference of 380 volts here?

not sure where the 380v is from but in reference to the permenent dividers, in Canada a system commonly used in commercial is 347/600. The boxes are a special design and also the holes for mounting only work for 347/600 switches. The partitions are red and are non conductive.

The book is assuming you have two wye systems, 120/208 3Ø and 277/480 3Ø, and that you are measuring from one phase, say A, on one system, and another phase, say B, on the other system.

The book is also assuming that there is one supply from the PoCo that is connected to both of the two system transformers, and the transformers have the same type of primaries. That results in the 120V AØ being almost exactly in step with the 277V AØ.

Measuring voltage from 120V AØ to 277V BØ results in 380 Volts.

Al