×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

SDS and common neutral

SDS and common neutral

SDS and common neutral

(OP)
So from what I've read, when you have a generator or other alternate power source, and transfer switch, each is a SDS, and that switch should switch the neutral as well. Neutral is grounded at the source.

But the case I'm looking at will have a utility xfmr w/wye secondary at the transfer switch, and an adjacent genset, and the inverters, all within a few feet. I would think all would share the same ground point -- the rod[s]+Ufer etc. at that point. If so, is there still a requirement to switch the neutral?

 

RE: SDS and common neutral

Hello,

In this case, I would recommend you:

1)Take a look at NEC, there is a whole chapter about grounding and as far as I remember there are some sections explicitly related to what you mentioned.

2)You should do an analysis about:
When you have as a source the xfmr, there will be a ground reference, because it is the basic scheme to feed your loads
When you have the genset, will the ground also be there?
Remember that ground is important to give a reference to your voltages and also the ground path has to be kept in order to allow ground protections to "do their job"
 

RE: SDS and common neutral

Although there are more complex systems where separate neutrals must be used to avoid ground loops, current sharing, and to facilitate ground fault detection, my preference is to ground the neutral if at all possible. In cases where a compromise must be made, I try to consider switching the neutral to be the last compromise.
The neutral may be common for the grid feed and for the generator. Solid neutral through the ATS.
I have seen expensive damage done several times when a switched neutral opened early or closed late. None of the systems was of a size or complexity to warrant neutral switching. I have never seen an issue with a solid neutral on a simple system.
How do you know if your system is simple or complex? Do you have a protection engineer determining the various settings on a sophisticated protection relay? No, then it may be a simple system.  If a complex system may be configured to allow a solid neutral, that is my choice also.
There are other opinions on this topic.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: SDS and common neutral

If all of the sources are close to each other, it will make more sense to ground the neutral only at the utility source and leave the generator neutrals ungrounded.  The generators will not be separately derived sources and the transfer switch would not switch the neutral.
 

RE: SDS and common neutral

Further to jghrist's post; the generator neutrals will be grounded by the main panel ground by virtue of the solid neutrals. Leaving the generator neutrals ungrounded would refer to not grounding the neutrals at the generator, but using the panel ground.
Often, the ATS has a neutral bus on which all incoming neutrals are connected. The main panel or location designated by the utility has the one ground on the system and that serves all sources.  

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: SDS and common neutral

(OP)

Quote:

Leaving the generator neutrals ungrounded would refer to not grounding the neutrals at the generator, but using the panel ground.

I sorta figured that out.


 

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources