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?
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
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
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
RE: SDS and common neutral
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
I sorta figured that out.