UPS a SDS?

Status
Not open for further replies.
Twoskinsoneman

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
Would you consider a UPS to be a Separately Derived System?
I'm designing a "Mobile UPS" that will connect between the utility and the building and backup the building electrical. 400v 3 pahse into "Mobile UPS", single phase 230v out. I'm trying to decide where I should bond the neutral at. The UPS is a not a bypass type. I'm thinking the "service" ends at the UPS and it is considered a feeder from there. But I'm also thinking that the UPS is a SDS.

What do you think?
Thanks
 
Twoskinsoneman said:
Would you consider a UPS to be a Separately Derived System?
I'm designing a "Mobile UPS" that will connect between the utility and the building and backup the building electrical. 400v 3 pahse into "Mobile UPS", single phase 230v out. I'm trying to decide where I should bond the neutral at. The UPS is a not a bypass type. I'm thinking the "service" ends at the UPS and it is considered a feeder from there. But I'm also thinking that the UPS is a SDS.

What do you think?
Thanks
Click to expand...

If you are not taking a neutral into the UPS and if the UPS is producing its own neutral than yes, it is a SDS.
Ideally, the neutral should be bonded in the UPS. But I think the NEC may let you go to the first overcurrent device.
 
Twoskinsoneman said:
Would you consider a UPS to be a Separately Derived System?
I'm designing a "Mobile UPS" that will connect between the utility and the building and backup the building electrical. 400v 3 pahse into "Mobile UPS", single phase 230v out. I'm trying to decide where I should bond the neutral at. The UPS is a not a bypass type. I'm thinking the "service" ends at the UPS and it is considered a feeder from there. But I'm also thinking that the UPS is a SDS.

What do you think?
Thanks
Click to expand...

From the technical viewpoint the UPS is an SDS in all modes except when is in the bypass mode.
 
If you brought the service neutral to the UPS and it is not bonded to the neutral that the ups derives then it a SDS.

If it is a SDS and you bond the neutral in the UPS then you will need a MBJ to the Equipment Ground from the UPS to the first system disconnect. (equipment ground buss).

I kind of think it is simpler to bond a SDS Neutral at the first disconnect. Were ever you bond the Neutral to the enclosure then all the bonding has to happen at that location, Neutral bond to enclosure, Neutral bond to Equipment grounding, Grounding electrode conductor connection to the Neutral. Or there has to be some type of MBJ between these connection points to the SDS neutral.

I believe the exception to this is when there is no other (other than SDS Neutral) metallic connection between the SDS and the first disconnect then you could bond the SDS Neutral at both locations without a MBJ between the SDS and the first disconnect. I don?t like doing it that way it just seems to confuse everything.

Again it?s just my opinion but I think it is simpler to do all the bonding at the first disconnect for most SDS.
 
Status
Not open for further replies.
Top