generator SDS

[ccha9219]

Maybe I'm not understanding the whole SDS/non SDS
thing.
To my way of thinking a generator is a serperate source of power. It should be wires as such.
Just because you switch the grounded conductor( or not) should be the detrmining factor if it a seperately derived system or not.
To me it's no different than a Back up transfomer. once you change the source of power you have a new service. right??

 

[roger]

Re: generator SDS

Ccha9219, this is a common misconception. What determines SDS or NON SDS is grounding

Go to the top of this page and click on search then type in SDS in the search window and click searc. Get your pop corn and be prepared for a stay.

Roger

 

[ccha9219]

Re: generator SDS

Roger,
I'm assuming you weren't talking about software data systems and companys that install and sell sds . Thats all That came up in the search.

 

[roger]

Re: generator SDS

You went to far up, click here and type in SDS, then click the search button at the bottom of the page.

Roger

[ February 26, 2004, 05:42 PM: Message edited by: roger ]

 

[ccha9219]

Re: generator SDS

Originally posted by roger:
Ccha9219, this is a common misconception. What determines SDS or NON SDS is grounding

Go to the top of this page and click on search then type in SDS in the search window and click searc. Get your pop corn and be prepared for a stay.

Roger

I'M still not understanding
If you go from utility power to the generator you have change the source from witch you get power
why doesn't the code address this issue as a new service? It's not that I dont understand all the diagrams you have posted, or how it all works....
A seperate source is a seperate source regardless of grounding or switched grounded conductors
If you have a 277/480 panel feeding a 50kva transformer that feeds a 120/240 panel, that panel is considered to be first means of dissconnect because the transformer is a new source.
So then it should stand to reason that if utility power goes down the gen set becomes your new source
This is where my confusion comes in, I don't understand way the code sees them differently

 

[roger]

Re: generator SDS

Ccha9219, think of it this way, a "separately derived system" would share no physical components with any other system.

If you don't switch the neutral, the two systems are physically and mechanically joined, verses being magnetically coupled or stand alone power sources.

In my opinion there are very few true SDS's in what we deal with do to the required bonding, but that is a different thread.

Roger

 

[ccha9219]

Re: generator SDS

Roger

So Even though the gen set is a different "source", It is not a separate "system" unless the grounded conductor is also switched at the ATS.
In my opinion all gen sets should be wired as a SDS with the appropriate ATS.

 

[iwire]

Re: generator SDS

Originally posted by ccha9219:
In my opinion all gen sets should be wired as a SDS with the appropriate ATS.

If you look at the previous posts on this subject some are very strongly opposed to ever switching the neutral.

Leaving the neutral connected poses absolutely no danger to the linemen.

Please explain the path you feel the current would have to take to prove hazardous to linemen?

 

[dereckbc]

Re: generator SDS

Originally posted by ccha9219:
So Even though the gen set is a different "source", It is not a separate "system" unless the grounded conductor is also switched at the ATS.
In my opinion all gen sets should be wired as a SDS with the appropriate ATS.

That is correct, it all depends on what you do with the neutral.

Here is another catch that throws some people, and is common practice. Assume you have a 3-phase generator, 3-pole ATS, bond the generator neutral to the frame and GES, and do not run a neutral from the generator. SDS or not?

Answer SDS.

 

[ccha9219]

Re: generator SDS

Originally posted by iwire:

Originally posted by ccha9219:
In my opinion all gen sets should be wired as a SDS with the appropriate ATS.

If you look at the previous posts on this subject some are very strongly opposed to ever switching the neutral.

Leaving the neutral connected poses absolutely no danger to the linemen.

Please explain the path you feel the current would have to take to prove hazardous to linemen?

I live in florida the lightning capitol of the usa. Unless the The nut. is broken at the ats, it is still going to get to the transformer via egc to the gec to the the utility grounded conductor.
The same would hold true if the gen set were to have short in the windings, without its own egc it would find its way back to ground at the transformer

 

[don_resqcapt19]

Re: generator SDS

ccha9219,

The same would hold true if the gen set were to have short in the windings, without its own egc it would find its way back to ground at the transformer

How and why would current from a generator winding short be going to the earth?????
Don

 

[ccha9219]

Re: generator SDS

i realized that right after I hit post reply

 

[iwire]

Re: generator SDS

Originally posted by ccha9219:
I live in florida the lightning capitol of the usa. Unless the The nut. is broken at the ats, it is still going to get to the transformer via egc to the gec to the the utility grounded conductor.

I am by no means an expert on lightning but I doubt that the little distance of separation between the open poles of a transfer switch is going to stop lightning.

It will jump that gap like it was not even there IMHO.

Originally posted by ccha9219:
The same would hold true if the gen set were to have short in the windings, without its own egc it would find its way back to ground at the transformer

I am still not seeing a complete circuit to cause a problem.

Any current produced by the generator only wants to go back to the generator not out to the POCOs transformer.

Wouldn't this current path be through the bonding jumper?

[ February 26, 2004, 06:57 PM: Message edited by: iwire ]

 

[hurk27]

Re: generator SDS

ccha9219

Current always returns to the source! Not Earth! This is one of the biggest misconceptions that has ever hit the electrical industry. and is one of the reasons that many AHJ's think that the GEC has to be protected nine ways from sunday. Current returns to source and the source in this case is the generator's own windings. Only when the load is being powered by the utility will the current return to the transformer and Still not Earth. the Earth has nothing to do with current path unless it becomes one of the conductors. If you run one wire to a lamp will it light? NO. but connect it to the neutral and it will this is because the neutral returns to the center tap (XO) on the transformer. now since the grounding in a building is also connected to the neutral via the MBJ in the service panel it to has a return path back to the transformer. now if that path is lost like in a neutral break then the Earth will not have a low enough impedance to carry the current back to the transformer which in turn will allow the neutral to float and when a load with a high enough current is turned on it will drop in voltage as the other leg goes high and distroys the equipment on that leg. also anyone touching any grounding connected to this lost neutral can be electrocuted. So this is why the Earth is not allowed to be the "SOLE RETURN PATH" for fault current.

 

[ccha9219]

Re: generator SDS

I see that I too was one of the misguided.
It was always put me that it wants to go back to
gound. even in theroy class the instructor always said "ground" not "source". Now I feel like a dope running my gator about something I knew to little about
Tonight I have learned something
Thank you

 

[iwire]

Re: generator SDS

Originally posted by ccha9219:
Now I feel like a dope

Don't feel like that, a dope is someone when presented with something new refuses to accept it may be true.

I have learned a ton from the members of this board and continue to do so.

I will never know all about this trade.