Is a UPS a separately derived source?

[samblv]

I was recently asked if a 400A UPS system is considered a "separately derived source" and therefore must be grounded as such?

Does anyone know if there are any qualifiers that would make this the case (or not)?

 

[jim dungar]

Does anyone know if there are any qualifiers that would make this the case (or not)?

If the UPS contains a by-pass circuit it is probably not a separately derived source.

 

[brian john]

If the UPS contains a by-pass circuit it is probably not a separately derived source.

Unless the bypass has a transformer.

 

[samblv]

Unless the bypass has a transformer.

The UPS feeds 5 separate PDU's ranging from 25KVA to 150KVA.

Does that mean anything?

 

[chris kennedy]

Does anyone know if there are any qualifiers that would make this the case (or not)?

I know this.

Separately Derived System.
A premises wiring system whose power is derived from a source of electric energy or equipment other than a service. Such systems have no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system.

 

[samblv]

I know this.

Now here's where I get a little confused. In a normal premise wiring system, we bring in utility power to the main switchboard, ground the neutral strip, bond the ground bus, then distribute to our loads. The neutral conductor is grounded only at the main switchboard; however, we carry a grounding conductor in all our feeder conduits and bond all the equipment along the way.

Now we introduce a UPS system with a by-pass switch and ground the nuetral for that system. The neutral conductor is grounded only at the UPS; however, we carry a grounding conductor in all our feeder conduits and bond all the equipment along the way.

Now for the money question:

Can we bond the equipment grounds for both systems together to prevent a potential difference between two pieces of equipment, adjacent to each other, but fed from different sources?

Or must each system be completely separate from the other?

 

[ron]

samblv,
It appears that this is a 4W output.
If there is a neutral in the incomming bypass feeder, you do not bond the neutral again at the UPS.
The bond already occured at the service entry.

 

[wirenut1980]

Now here's where I get a little confused. In a normal premise wiring system, we bring in utility power to the main switchboard, ground the neutral strip, bond the ground bus, then distribute to our loads. The neutral conductor is grounded only at the main switchboard; however, we carry a grounding conductor in all our feeder conduits and bond all the equipment along the way.

Now we introduce a UPS system with a by-pass switch and ground the nuetral for that system. The neutral conductor is grounded only at the UPS; however, we carry a grounding conductor in all our feeder conduits and bond all the equipment along the way.

Now for the money question:

Can we bond the equipment grounds for both systems together to prevent a potential difference between two pieces of equipment, adjacent to each other, but fed from different sources?

Or must each system be completely separate from the other?

In my opinion, the equipment grounds should not be bonded together, however, the two grounding electrode systems should be bonded together to eliminate the possibility of potential difference being developed across the two systems.

 

[Cold Fusion]

In my opinion, the equipment grounds should not be bonded together, however, the two grounding electrode systems should be bonded together to eliminate the possibility of potential difference being developed across the two systems.

Wirenut -
I'm.

I work industrial exclusively. Each site will have several transformers and UPSs. However ther will only be one grounding electrode system. It may be 100 rods, ground mats in selected areas, dozens of steel piling, dozens of CCEs - they are all connected.

Every SDS, that is a grounded system, will have its grounded conductor connected to the one and only grounding electrode system.

So, I am missing what you are saying.

cf

 

[wirenut1980]

Wirenut -
I'm.

I work industrial exclusively. Each site will have several transformers and UPSs. However ther will only be one grounding electrode system. It may be 100 rods, ground mats in selected areas, dozens of steel piling, dozens of CCEs - they are all connected.

Every SDS, that is a grounded system, will have its grounded conductor connected to the one and only grounding electrode system.

So, I am missing what you are saying.

cf

CF,

What you are talking about is fine and well. There are plenty of installations like that. I am speaking more from a ground potential difference point of view where say you have two services to a building. Sometimes the two services GES's are not connected together. Each service feeds computers. Those computers are connected together over a network. Assuming the network is not fiber optic, there could be a potential developed across the computers.

It sounds to me like the OP has a similar situation with two GES's. If they are already tied together, then all should be fine. But I have always seen the GES's bonded together and not the EGC's at equipment from two separate systems bonded together...not sure if there is a difference electrically.