Separately Derived Systems

[ZCBee]

I have some confusion on how to determine a separately derived system and was wondering if someone might be able to shed some light on this.

If you bring in a 480V feed that is properly bonded to an industrial control panel that has a control transformer stepping down the voltage to 120 volts, the load side of said transformer is the point of this 120 volts systems origin and therefore one transformer tap must be bonded, correct?

What about a 25 volt instrumentation transformer? Thanks

 

[augie47]

I have some confusion on how to determine a separately derived system and was wondering if someone might be able to shed some light on this.

If you bring in a 480V feed that is properly bonded to an industrial control panel that has a control transformer stepping down the voltage to 120 volts, the load side of said transformer is the point of this 120 volts systems origin and therefore one transformer tap must be bonded, correct?

Look at 250.30(3)-Exception. Under some circumstances they do not need to be bonded

What about a 25 volt instrumentation transformer? Thanks

Look at 250.20(A). There are conditions where they must be grounded.

 

[ZCBee]

Look at 250.30(3)-Exception. Under some circumstances they do not need to be bonded

Look at 250.20(A). There are conditions where they must be grounded.

So, if I feed the instrumentation xfmr from the 120v secondary, I do not need a system ground for the 24V xfmr. But, if I were providing the 480V to the primary, I would need a system ground for the 24V secondary. Thank you, makes sense!