SDS/Generator grounding help

[roger]

Re: SDS/Generator grounding help

ED, the problem I have is not the terminalogy of SDS, and in reality this is closer than "isolated". I would see isolated as "Ungrounded Delta / Ungrounded Delta , some Control transformers, Healthcare isolaton systems, bla bla bla ...

I am also tired of these conversations, tried to stay out of this one, and frankly don't care if anything ever changes, but when we deal with all the problems of net currents, ground loops, EMF's and other grounding and bonding caused problems and issues, I just can't stand to see the reckless notion that grounding and bonding are not "direct electrical connections".

Roger

 

[browningcw]

Re: SDS/Generator grounding help

Boy, did I open a can of worms!

Great discussion between very qualified people is a wonderful thing!

 

[iwire]

Re: SDS/Generator grounding help

I am tired of the Name Game too, if they want to call the typical 480-208/120 transformer an SDS fine, it is a new voltage system.

I do not care if the call it a "box of electrons'.

What I had or have a problem with is the NFPA saying

Connections of these conductors to a common grounding system are not connections of the circuit conductors directly to each other

Call the transformer whatever you want we all know how we are expected to hook it up, but do not tell me a connection is not a connection.

Even though I am to thick headed to get it, I still know how they expect me to ground and bond this transformer.

I'll shut up now as this has been talked to death.

Bob

 

[don_resqcapt19]

Re: SDS/Generator grounding help

Bob,
The definition could be worded differently, but the point is that there is no "direct" connection of conductors that carry current under normal conditions. Yes, there is a connection between the primary and secondary grounded conductors, but this is not a "direct" connection. The two grounded conductors are not physically connected to each other, but they are electrically connected to each other via the grounding conductors.
Don

 

[Ed MacLaren]

Re: SDS/Generator grounding help

we deal with all the problems of net currents, ground loops, EMF's and other grounding and bonding caused problems and issues

Do I understand the statement to mean that grounding and bonding per the NEC causes the problems referred to?

Below is a sketch of the "systems" involved in a typical building service.

Perhaps someone could indicate which of the grounding/bonding connections would cause such problems, assuming the systems are properly installed and maintained?

Ed

 

[roger]

Re: SDS/Generator grounding help

Ed,

Do I understand the statement to mean that grounding and bonding per the NEC causes the problems referred to?

no, grounding and bonding per anyones codes can cause this.

assuming the systems are properly installed and maintained?

a big assumption considering all the time spent tracking down these problems.

Perhaps someone could indicate which of the grounding/bonding connections would cause such problems,

any connection point of the system where a surge, fault, or current could parallel your green and gray conductors. Yes, this would be when the system is experiencing a problem, the main reason for grounding and bonding.

Ed can you explain per your drawing how anyone can argue that the grounding and bonding is not directly connected to the windings of the transformers and back to the MGN upstream of the "pad mount" which directly joins all together.

Let's forget about SDS and Isolation for now and explain how grounding and bonding is not direct electrical connections. It seems this is another area that has redefined language and words.

Roger

[ August 13, 2003, 06:49 PM: Message edited by: roger ]

 

[Ed MacLaren]

Re: SDS/Generator grounding help

explain per your drawing how anyone can argue that the grounding and bonding is not directly connected to the windings of the transformers and back to the MGN upstream of the "pad mount" which directly joins all together.

Sure, there is a connection. I wouldn't try to argue that, because you can see the connection with your own eyes.

But, here's the important point, what harm does it do?
There is only a single grounding/bonding connection between any of the three "systems". For objectionable current to flow there would have to be a circuit from one of the systems to another.

The following may be obvious but, sometimes we tend to forget.
The current, both normal load and fault current, if any, in a system flows only within the conductors of that system.

For example, in the sketch, all of the current flowing out of the 480 volt (padmount) secondary flows only through the 480 volt primary of the drytype, (plus any other 480 volt loads) and back to the 480 volt secondary. None of it flows in either of the other two systems.

Even in the event of a circuit fault, current will only flow back to it's source. It may follow various paths, but only those that form a complete circuit back to it's source.

Ed

[ August 13, 2003, 08:13 PM: Message edited by: Ed MacLaren ]

 

[roger]

Re: SDS/Generator grounding help

Ed, although rare, you and I know there is a fault which will span both primary and secondary circuits, (p winding to s winding) so how can we say

The current, both normal load and fault current, if any, in a system flows only within the conductors of that system.

For example, in the sketch, all of the current flowing out of the 480 volt (padmount) secondary flows only through the 480 volt primary of the drytype, (plus any other 480 volt loads) and back to the 480 volt secondary. None of it flows in either of the other two systems.

as a blanket statement?

In the right (if there is such a thing) fault, every item in your drawing is seeing voltage and current physically connected through more than magnetic coupling.


Roger

[ August 13, 2003, 09:19 PM: Message edited by: roger ]

 

[don_resqcapt19]

Re: SDS/Generator grounding help

Roger,
Can you show me, in Ed's drawing, where the gray conductor of one voltage system is directly, physically connected to the gray conductor of the other voltage system? Yes, they are electrically connected by the green wires, but they are not physically connected to each other. This is all that the code is saying. This is in contrast to an autotransformer where the grounded conductors of both voltage systems are in actual physical contact with each other.
Don

 

[roger]

Re: SDS/Generator grounding help

Don, with all due respect, and I mean that from the bottom of my heart, I don't know how to respond to this.


you said

Can you show me, in Ed's drawing, where the gray conductor of one voltage system is directly, physically connected to the gray conductor of the other voltage system? Yes, they are electrically connected by the green wires

I am done with this thread.

Roger

 

[don_resqcapt19]

Re: SDS/Generator grounding help

Roger,
I'm just stating, my opinion of what the words in the code say. I didn't say that they really make a lot of sense, but that is what they appear to say, and the panel has stated the same thing.
From panel comment on proposal 1-135:

... Connections of these conductors to a common grounding system are not connections of the circuit conductors directly to each other.

Don

[ August 13, 2003, 10:10 PM: Message edited by: don_resqcapt19 ]

 

[tom baker]

Re: SDS/Generator grounding help

Don-thanks for straightening me out on the SDS. We see a lot of this generator - SDS questions, I didn't see the part about no neutral present.

 

[pierre]

Re: SDS/Generator grounding help

It is sometimes difficult for us to properly convey our ideas as we would like to on this forum. Therefore some might not completely understand what another is trying to convey in his/her post and it can be frustrating.
I have stayed away from posting here, but now feel compelled to respond and I will keep it relatively short.

1. Don's comment about most people not reading the ROPs and ROCs is very much appropriate. Sometimes the CMP members themselves have a hard time wording the sections and it does not always come out as they like. The reading of the ROP and ROC helps toward the understanding of what they are trying to say.

2. Knowing the history of the code process can also be very valuable in the understanding of a code rule.

3. Roger I can understand your frustration, but all the different 'opinions' here are what makes this forum as good as it is. I know that you understand that as well.

4. The confusion that surrounds this subject, and others as well in our industry, are IMHO what makes it such an interesting industry.

5. By BANGING OUT this issue as much as it has been in this and other forums has helped me tremendously to better understand this subject (I am a slow learner). So sometimes for the benefit of us 'slow learners' these long drawn out threads are beneficial.

Thanks!!!

Pierre