250.35

[TimK]

Can someone help me see how a permanently installed generator would be a nonseperately derived system? Do they install it and run it with normal power (POCO)?

 

[Dennis Alwon]

Can someone help me see how a permanently installed generator would be a nonseperately derived system? Do they install it and run it with normal power (POCO)?

Basically if you switch the neutral on a generator in the transfer switch then you have a SDS. If the neutral is not switched then it is not a SDS

 

[TimK]

Basically if you switch the neutral on a generator in the transfer switch then you have a SDS. If the neutral is not switched then it is not a SDS

Okay, what made us come up with that? When a service comes into a building it is not switched and that is SDS. Normally inside the building you don't run a nuet to the transformer, but if I wanted to and not switch it, could i call it nonSDS and not do all the bonding and grounding that is required?

 

[texie]

You may be confusing a separately derived system with a paralleled system. As dennis said, separately derived system, as it relates to a generator, has to do with how the neutral is handled. In a paralleled system it could run in parallel with the utility and/or other generator set(s).

 

[TimK]

You may be confusing a separately derived system with a paralleled system. As dennis said, separately derived system, as it relates to a generator, has to do with how the neutral is handled. In a paralleled system it could run in parallel with the utility and/or other generator set(s).

I do apologize, I am not trying to be stubborn. So if it is not a SDS than it is parallel or nonSDS?

 

[augie47]

A generator can be either an SDS on not an SDS depending on the neutral being switched ( Check the definition of a SDS.).
Grounding is handled differently depending on the genny being a SDS or not.
A majority of the installs where the generator is "standby power" do not switch the neutral, therefore the generator is not wired as a SDS.

 

[TimK]

A generator can be either an SDS on not an SDS depending on the neutral being switched ( Check the definition of a SDS.).
Grounding is handled differently depending on the genny being a SDS or not.
A majority of the installs where the generator is "standby power" do not switch the neutral, therefore the generator is not wired as a SDS.

Thanks everybody for making that clear as mud. just kidden. I have read that before, but never realized the second sentance had such an impact. Read the first sentance and it tells you everything you need to know. Nope, keep reading Tim, it ain't clickin! Once again thanks all for your help.

 

[texie]

I do apologize, I am not trying to be stubborn. So if it is not a SDS than it is parallel or nonSDS?

As Augi said, it is SDS or not SDS. Parallel operation is whole different subject and a lot more complex. An SDS connected generator is not as common as a non-SDS, but is used (SDS) for example, on larger services where GF protection is involved. Just remember that SDS or non-SDS in most generator setups, they do not run in parallel with each other or the utility-the power source is utility OR generator to the load. In a parallel setup you could have utility and generator(s) supplying the load at the same time.
No need to apologize, you ask good questions.

 

[TimK]

As Augi said, it is SDS or not SDS. Parallel operation is whole different subject and a lot more complex. An SDS connected generator is not as common as a non-SDS, but is used (SDS) for example, on larger services where GF protection is involved. Just remember that SDS or non-SDS in most generator setups, they do not run in parallel with each other or the utility-the power source is utility OR generator to the load. In a parallel setup you could have utility and generator(s) supplying the load at the same time.
No need to apologize, you ask good questions.

I do completely understand the parallel, thats the one I can picture in my head, I guess that I don't see why switching nuetral makes it seprately derived or not?

 

[petersonra]

I do completely understand the parallel, thats the one I can picture in my head, I guess that I don't see why switching nuetral makes it seprately derived or not?

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
connection from circuit conductors of one system to
circuit conductors of another system, other than connections
through the earth, metal enclosures, metallic raceways,
or equipment grounding conductors.

So by definition, a generator that is an SDS has to have the neutral switched or it would have conductors in common and thus not be an SDS.

 

[TimK]

So by definition, a generator that is an SDS has to have the neutral switched or it would have conductors in common and thus not be an SDS.

Okay, we are narrowing the point a little at a time, I might be quick that way. I can understand why you would switch the neut, GF and all that, but why would you not? I always took separately derived as a second source of power.

 

[Dennis Alwon]

Okay, we are narrowing the point a little at a time, I might be quick that way. I can understand why you would switch the neut, GF and all that, but why would you not? I always took separately derived as a second source of power.

Money-- it cost more to switch the neutral but there may be other reasons- IDK

 

[ActionDave]

Money-- it cost more to switch the neutral but there may be other reasons- IDK

That and the fact that in most cases there is no need to.

 

[kwired]

Once you open the neutral conductor with the transfer switch, the generator is isolated, if you never open the neutral to the generator, that system is always tied into the grounding system of the premises wiring.