separately derived systems

[stafelectric@yahoo.com]

Why would you call a transformer a separately derived system? If everything comes though the same meter.Wouldn't you need another meter or power bill to be separately derived system?

 

[raider1]

Here is the NEC definition of separately derived system.

Separately Derived System. A premises wiring system
whose power is derived from a source of electric energy or
equipment other than a service. Such systems have no direct
connection from circuit conductors of one system to
circuit conductors of another system, other than connections
through the earth, metal enclosures, metallic raceways,
or equipment grounding conductors.

You will note that the definition does not say anything about meters.

Chris

 

[charlie b]

Think of it in these terms: Electric current will seek all available paths back to its source. Current that leaves a transformer, flows through a panelboard and on to a load, will return to the panelboard and to the transformer, before starting its circular journey again. This current will not flow back to the main panel, and does not flow through the main meter. It is a separate system. It is created, or derived, by the transformer, and the absence of a direct connection between primary and secondary windings is what maintains the separation.