# three phase system

J

#### juigi

i just want to ask if it is possible to use the potential earth of a 3 phase system as a zero wire? is there 220 v between phase and potential erath. pls explain the details.

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#### Phil Corso, PE

Juigi, in response to your 01-Dec (10:48) question...

By electrical-code (NEC in the USA) the earth-plane is not permitted to carry continous current. Such currents are referred to as "objectional currents!"

However, there are several exceptions! One, is related to protective device operation, i.e., for the time it takes to clear a phase-to-earth fault! Another is a current resulting from cathodic-protection systems. And a third is a current resulting from "noisy" electronic or data systems.

An un-earthed system can result in "objectional currents" if the phase-to-earth capacitance is unbalanced! Such conditions are considered a shock hazard, and must be corrected as quickly as possible! Especially in Hazardous (Classified) Locations!

Regards, Phil Corso ([email protected])