Grounding Separately Derivied Systems Article 250.30

[dereckbc]

Re: Grounding Separately Derivied Systems Article 250.30

KQRESQ, what would be wrong with running the GEC to the transformer with the primary phase conductors as long as it is sized per 250.66 for the derived secondary conductors, and terminated to the Xo? You could use the metalic raceway as the EGC for the primary protection.

Provided the GEC is bonded to the metalic raceway at each end, I cannot see how that would be a problem with the code as long as it originated from the service.

 

[kqresq]

Re: Grounding Separately Derivied Systems Article 250.30

The original post does not say that there is any metallic conduit. For all I know, the transformer is fed by underground PVC. I try never to assume.

 

[pierre]

Re: Grounding Separately Derivied Systems Article 250.30

Okay here I go again.
I know what a separately derived system is, but... if one were to run the GEC with the primary conductors would that not make this a moot point? Or is it only when the Grounded Conductor is mechanically and electrically not connected that it is a separately derived system?

Bennie,
I am confused and I am going to ask for your help. If my slow response to understanding this is irritating you, just don't respond and I will get the message. But I need to see if I understand this or not.

kqresq: In 250.30 where do you see anything about a ground electrode conductor on the X-O of a transformer?

This is from your July 3rd 1:09 am post.
Is not the answer to this, 250.30(A)(2)(a), the last sentence before the exception ", this connection shall be made at the same point on the separately derived sustem where the bonding jumper is installed."?

Thanks for working with me on this

Pierre

 

[kqresq]

Re: Grounding Separately Derivied Systems Article 250.30

Bennie, 250.30 does not "permit" the XO to connect to the grounding electrode, It requires it to do so.

Does anybody think that the following has any bearing?
250.64(C) Continuous. The grounding electrode conductor shall be installed in one continuous length without a splice or joint, unless spliced only by irreversible compression-type connectors listed for the purpose or by the exothermic welding process.
Exception: Sections of busbars shall be permitted to be connected together to form a grounding electrode conductor.

Would the connection at the busbar be considered a "joint"?
If there is no metallic conduit to use as the EGC, is anyone proposing the conductor sized per 250.66 can double as both the EGC and the GEC?

 

[gwz2]

Re: Grounding Separately Derivied Systems Article 250.30

Pierre,

Note the last sentence of the first paragraph of 250.30(A)(4).
"The grounding electrode SHALL be the nearest of the following:"

The combination run of primary EGC and the Secondary GEC could possibly be the Feeder EGC.

 

[bennie]

Re: Grounding Separately Derivied Systems Article 250.30

kqresq: A transformer does no require a ground electrode. An equipment ground conductor is all that is necessary.

A separately derived system requires a ground electrode conductor.

 

[roger]

Re: Grounding Separately Derivied Systems Article 250.30

kqresq, one question, in your opinion are GEC's and EGC's electrical connections?

Roger

 

[kqresq]

Re: Grounding Separately Derivied Systems Article 250.30

Bennie, 2002 NEC Art. 100 Definitions
Separately Derived System. A premises wiring system whose power is derived from a battery, from a solar photovoltaic system, or from a generator, transformer, or converter windings, and that has no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system.
In the several jurisdictions that I have worked in, a common delta/wye voltage transformer has always been considered to be a separately derived system as defined by the NEC.

 

[kqresq]

Re: Grounding Separately Derivied Systems Article 250.30

Roger,
At the risk of being corrected no matter how I answer; no. In a properly functioning system the GEC and EGC are not electrical connections because they are not intended to normally have any current flow except in a fault and/or surge situation.

By the way guys,
I am not trying to be argumentative. I am just trying to determine what the NEC says, as opposed to anyones opinion about "how it ought to be".

 

[roger]

Re: Grounding Separately Derivied Systems Article 250.30

kqresq, I know you have been here for awhile but not very active.

So, let me say WELCOME to the forum.

I'm not responding to your post yet.

Roger

 

[bennie]

Re: Grounding Separately Derivied Systems Article 250.30

kqresq: Read 200.3

Also...A transformer is the power source for a separately derived system. It is not the separately derived system.

The definition clearly spells out...A separately derived system is a premises wiring system.

[ July 03, 2003, 11:04 PM: Message edited by: bennie ]

 

[kqresq]

Re: Grounding Separately Derivied Systems Article 250.30

Here is a link to the August 1, 2001 edition of Electrical Construction & Maintenance magazine.

http://www.ecmweb.com/ar/electric_separately_derived_system/


The article describes separately derived systems as follows:

Separately derived systems are power sources with no direct electrical connection between any of the circuit conductors and supply conductors. For example, no direct connection exists between the primary and secondary winding of a delta-wye transformer.

the author of this reads:

By Mike Holt, Mike Holt Enterprises, Inc.

 

[bennie]

Re: Grounding Separately Derivied Systems Article 250.30

Of all the code experts I respect Mike Holt more than any. I have had occasion to talk to him personally, on the land line.

His statement is the mainstream of the correct interpretation of a separately derived system.

However there is no basis to consider a transformer a separately derived system.

The windings of a delta wye transformer are solidly connected electrically, mechanically, and physically. The definition in 200.3 makes it clear that a conductor is electrically connected if it is capable of carrying current.

The origin of separately derived system was "isolated systems" in 1908, later it became AC systems without external connections, then in 1956 it became separately derived systems. The premises wiring system is the subject, not the power source.

 

[kqresq]

Re: Grounding Separately Derivied Systems Article 250.30

Don,
I found an article explaining the exception you mentioned earlier. This would seem to negate 250.64(C)in certain applications. (I think this is from the 1999 NEC)

250-30(a)(1)
The rules have been changed for the grounding of a separately derived AC system. The rule states that the bonding of grounding electrode and the grounded conductor shall take place at the same location, either at the source or at the disconnecting means. Also, there shall not be a bonding of the grounded conductor at the source and at the disconnecting means unless it is assured that there will not be parallel paths for current carried by the grounded conductor. The earth is not considered a parallel path.
The grounding electrode is required to be the nearest of 1) the effectively grounded metal structural member, 2) grounded water pipe, or 3) other electrodes meeting 250-50 (old 250-81). The connection to the water pipe shall be within five feet from the point of entrance into the building.
A very important exception has been added at 250-30(a)(3)(c) Exception for separately derived systems that originate from listed service equipment. In these cases, the service grounding electrode is permitted to be the grounding electrode for the separately derived system. The internal ground bus that is not smaller than the required grounding electrode conductor is permitted to be the connection point for the separately derived system.

Author's Comment

The proposal for this change [5-116a] was submitted by Code Making Panel 5 in the rewriting of section 250-26 of the 1996 Code. For years engineers have been using the service equipment grounding electrode as the grounding electrode for separately derived AC systems and have been installing the grounding electrode conductor as a the primary equipment grounding conductor. The two conductors are the same in many installations. The Code now allows this in the new exception to 250-30(a)(c)(3).