Generators- separately derived system

[aelectricalman]

Since they are a separately derived system, can the grounding be done via earth ground at the unit or the ATS rather than bringing equipment ground from the gen set to the building. The ATS is the first point of entry for the gen. I should be able to bring my ungrounded coonductor and my neutral to that point. The grounding would be derived from earth at the the ATS, right? Long story short, I have an inspector telling me I need to bring 3 hots, 1 Neutral and 1 equipment ground from the gen to the ATS. Im not sold.

 

[goldstar]

I believe the inspector is correct. You have to re-establish the ground by installing a ground rod at the generator when transferring the neutral (separately derived system). You also have to tie all the grounds together (i.e the ground wire from the ATS) in order to establish a common bonding grid. Look at 250.30 (2008 code)

 

[augie47]

Since they are a separately derived system,.

"They" are not always a SDS, in fact, most are not.
Does the ATS switch the neutral ? (if not, then it's not an SDS)

can the grounding be done via earth ground at the unit or the ATS rather than bringing equipment ground from the gen set to the building. The ATS is the first point of entry for the gen. I should be able to bring my ungrounded coonductor and my neutral to that point. The grounding would be derived from earth at the the ATS, right? Long story short, I have an inspector telling me I need to bring 3 hots, 1 Neutral and 1 equipment ground from the gen to the ATS. Im not sold.

Is there a OCP at the generator ?

 

[aelectricalman]

Suppose the Generator has no overcurrent protection device. Hypothetical. Not the case. Any bearing?

 

[aelectricalman]

I missed your quote Augie47. Would that change the
formula?

 

[Smart $]

Suppose the Generator has no overcurrent protection device. Hypothetical. Not the case. Any bearing?

I missed your quote Augie47. Would that change the
formula?

I can't think of any scenario where no grounding conductor would be compliant. The only thing that changes is the grounding conductors' size and whether there is a system bonding jumper and its location. On the supply side of the OCPD, grounding conductor is sized per 250.66. On the load side per 250.122.

Another grounding issue for an SDS systems is meeting the Grounding Electrode requirement.