SDS Grounding/Bonding.. Ground Loop?

[winnie]

Wow never thought of it that way, thanks. But would you carry 4 wire back to first panel as implied in the original image posted by jerramundi or just the bonding ground?

I thought it was 3 wire plus egc on the primary side. There is no need to bring the primary neutral to the transformer unless it is an atypical wye-wye transformer. (And if it is such then the bulk of this discussion goes out the window.....)

Jon

 

[Fred B]

I thought it was 3 wire plus egc on the primary side. There is no need to bring the primary neutral to the transformer unless it is an atypical wye-wye transformer. (And if it is such then the bulk of this discussion goes out the window.....)

Jon

Do you mean 2 wire plus ground, this illustration was if I saw it right was single phase, above reference would for 3 phase if I understand you.

 

[winnie]

I was assuming 3 phase, but you are correct the illustration is single phase.

Jon

 

[Jerramundi]

Thanks for the clarification, I think my confusion was with the original drawing showing the neutral carrying past the transformer not ending at secondary winding. I got stuck on the neutral, But i guess it would just change purpose at that transformer bonding with the grounding system and tieing back to the original panel. Is that right?

While I admit the drawing is somewhat crude, the neutral DOES NOT carry past the transformer in either direction (from (1) primary to secondary OR (2) secondary to primary).

The orange marking was attempting to highlight a potential GROUND FAULT current pathway that linked (via the bonding of metal parts, etc) the secondary and primary neutrals and that was the concern I was asking to be addressed because these two neutrals are supposed to be isolated in an Separately Derived System (SDS).

Others input helped, but Don ultimately clarified this in Post #30 by quoting the definition of an SDS, which clarified that there will be a connection between the two sources via grounding and bonding connections.

Separately Derived System. An electrical source, other than a service, having no direct connection(s) to circuit conductors of
any other electrical source other than those established by grounding and bonding connections.

 

[Jerramundi]

What would happen to your concern if there were no primary?

I guess I'm just being excessive and imagining a transformer where the enclosure is split in two? In other words, somehow there is isolation between the primary side of the enclosure and secondary side of the enclosure... and thus truly 100% separation between the grounding and bonding systems of an SDS (other than the Earth).

 

[LarryFine]

The orange marking was attempting to highlight a potential GROUND FAULT current pathway that linked (via the bonding of metal parts, etc) the secondary and primary neutrals and that was the concern I was asking to be addressed because these two neutrals are supposed to be isolated in an Separately Derived System (SDS).

Others input helped, but Don ultimately clarified this in Post #30 by quoting the definition of an SDS, which clarified that there will be a connection between the two sources via grounding and bonding connections.

You're still mixing up two different ideas: the behavior of electricity and a code definition.

Again, fault current on the secondary will not attempt to flow toward the primary supply.

Your question was about neutral current on the orange pathway, not code compliance.

 

[winnie]

I guess I'm just being excessive and imagining a transformer where the enclosure is split in two? In other words, somehow there is isolation between the primary side of the enclosure and secondary side of the enclosure... and thus truly 100% separation between the grounding and bonding systems of an SDS (other than the Earth).

As I mentioned there is capacitive coupling between primary and secondary. For some specialized application this coupling is a problem and there are special transformers wound with capacitive shielding between primary and secondary.

Usually these are for signals rather than power distribution, but I think some high voltage step up/down transformers require capacitive shielding.

Jon

 

[Jerramundi]

You're still mixing up two different ideas: the behavior of electricity and a code definition.

Again, fault current on the secondary will not attempt to flow toward the primary supply.

Your question was about neutral current on the orange pathway, not code compliance.

With respect, I don't see how I'm "mixing up two different ideas: the behavior of electricity and a code definition."
I understand that the physics of electricity is different from code requirements, but would argue that the two are inextricably linked.

Perhaps I misspoke at some point, but my question was never really "about neutral current on the orange pathway."

It was about the issue of having multiple neutral to ground connections, which I was concerned about via the orange pathway in the diagram. I never explicitly claimed that pathway to be "neutral current," but was merely attempting to highlight a potential connection between two different neutral to ground connections via the grounding/bonding systems... which was clarified to me is acceptable according to the definition of an SDS as long as said connection is strictly limited to the grounding/bonding systems.

It's my understanding that the separation of these different neutral to ground connections is something that is both based on the behavior of electricity and code compliance.

Freb B posited that the neutral in my diagram was extending beyond the transformer's point of isolation and I was simply clarifying that it was not.

 

[LarryFine]

My apologies.

 

[Jerramundi]

All good. No need to apologize. I'm definitely still learning in some areas, especially transformers/SDS' and appreciate any and all help I can get.

I just wanted to clarify Fred's comment that my diagram had the neutral extending beyond the point of isolation, because to me, this was a mischaracterization of something I already knew.

My apologies if I got a little defensive because of this. Definitely appreciate all the help you've given

 

[Fred B]

Sorry I misinterpreted the orange to be the neutral it appeared to be originating at the neutral of the second panel going back to the first thru the trans.

 

[Jerramundi]

Sorry I misinterpreted the orange to be the neutral it appeared to be originating at the neutral of the second panel going back to the first thru the trans.

All good.

 

[electrofelon]

It was about the issue of having multiple neutral to ground connections, which I was concerned about via the orange pathway in the diagram.

In a grounded system, there will often be multiple N-G connections, its just the way it is and is unavoidable. For one thing everything on the supply side is bonded to the grounded conductor, and these things could have multiple connections to dirt. The wording of the code is such that it kinda implies there is ONE GEC and ONE MBJ, but systems are often not installed that way, and besides we have the unavoidable stuff like a metal service raceway going into the dirt.

See 250.24(A)(5) and 250.142. Note that they dont require a single point earthing system.

 

[winnie]

Don't confuse utility systems, utility to building services, and pure NEC controlled installations.

The utility intentionally uses 'multi earth neutral' installations and for better or worse neutral current intentionally flows through the soil.

Services from the utility have neutral to ground bonds, even though several services share the same transformer. This means multiple neutral to earth bonds, see threads about plumbers being shocked because of this.

But in a pure NEC installation there should be a single connection between neutral and the grounding system.

The confusion in the OP was the connection between _different_ system neutrals via the grounding system and the connection of the grounding system to multiple earth electrodes.

Jon

 

[don_resqcapt19]

...
It's my understanding that the separation of these different neutral to ground connections is something that is both based on the behavior of electricity and code compliance. ...

There is no separation of different neutral to ground connections in a code compliant installation. Each system has only one neutral to ground connection at a single location (with the exception of a service where there is an utility neutral connection at the transformer, and a code neutral to ground connection at the service equipment) but the grounding systems for all of the systems are connected together.

 

[winnie]

There is no separation of different neutral to ground connections in a code compliant installation. Each system has only one neutral to ground connection at a single location (with the exception of a service where there is an utility neutral connection at the transformer, and a code neutral to ground connection at the service equipment) but the grounding systems for all of the systems are connected together.

Clarifying just because it has been a point of confusion:

Grounded/bonded metal consists of the various plumbing pipes, building structure, grounding electrodes and grounding electrode conductors, etc. All of the metal that isn't intended to carry current normally but which might carry current during fault conditions. This metal may connect to 'soil' in multiple locations.

Each neutral gets connected to the above grounded/bonded metal at _one_ location on the neutral circuit. This _single_ connection might result in many separate connections to soil, but it is a _single_ point on the current carrying conductor that gets connected.

-Jon

 

[Jerramundi]

There is no separation of different neutral to ground connections in a code compliant installation. Each system has only one neutral to ground connection at a single location (with the exception of a service where there is an utility neutral connection at the transformer, and a code neutral to ground connection at the service equipment) but the grounding systems for all of the systems are connected together.

IMHO, you seem to contradict yourself here. How can you state that both (1) there is no separation different between neutral to ground connections AND (2) Each system has only one neutral to ground connection?

It is NOT incorrect to say that you are required by code to separate the different neutral to ground connections.

There is clearly code required separation between the different neutral to ground connections per the restrictions on load side neutral to case/ground connections.

It's just that, as I've recently learned and as you've just stated, there are exceptions for an SDS, which per its' definition, allow for a grounding/bonding link between the different neutral to ground connections.

But this exception does NOT mean that there is NO required separation.

 

[electrofelon]

Each neutral gets connected to the above grounded/bonded metal at _one_ location on the neutral circuit. This _single_ connection might result in many separate connections to soil, but it is a _single_ point on the current carrying conductor that gets connected.

-Jon

I am going to disagree some Jon. I do not see that as being clear in the code that a single point earthing system is required. It is not explicitly stated and I can not come up with a definitive requirement looking at the definitions of things like GEC and MBJ. It is quite common to have two GEC's for a service connected at different points, such as the rods in the meter and the water do the main disconnect inside.

Also there would be the inadvertent connection to soil thru say thru an underground RGS service conduit.

 

[Jerramundi]

The comment of mine that you are responding to was to address Larry's statement that I was "mixing up" different ideas (i.e. the behavior of electricity and code requirements)... in that these neutral to ground connections are code requirements that are based on the behavior of electricity. In other words, that code requirements and the behavior of electricity are intrinsically linked... albeit to Larry's point, often addressed separately.

 

[Jerramundi]

It is quite common to have two GEC's for a service connected at different points, such as the rods in the meter and the water do the main disconnect inside.

Interesting point of contention. I suppose there are two GEC's, but are they both not supply side connections? I believe there is an explicit section of code that prevents load side neutral to ground connections precisely because there already exists a supply side connection (or connections)... and this restriction prevents the flow of objectionable current.