Transformer Neutral Connections

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Dave_C

New member
We have been contracted to install some equipment, in a large room, at a customers site. The facility power entering the room is 208VAC 3-phase wye power with both a neutral conductor and a ground conductor. The equipment requires 480VAC 3-phase wye power. Therefore we intend to use a delta-wye 208:480 75KVA transformer.

My questions are:
1) Would the 480VAC power be considered a separately derived system?
2) Can or should the facility neutral conductor be connected to the transformer secondary neutral (X0 terminal)?
3) Can the facility ground wire be used as the GEC to ground the secondary neutral (X0 terminal), provided it is sized properly for both the primary and secondary currents, or does it have to be a local ground such as building steel or a water pipe?
4) Can or should you connect both the facility neutral conductor and a GEC wire to the transformer secondary X0 terminal?

Thanks
 

benaround

Senior Member
Location
Arizona
At the recent Section meeting, there were 2 members of CMP #5. the told us that a GEC and an EGC are separate conductors and not to have one conductor provide both uses. I believe there is wording in the 2011 proposals that has been accepted in regards to this.

Pierre,

So you agree with my answers. I have never been on the dual use camp .
 

Smart $

Esteemed Member
Location
Ohio
At the recent Section meeting, there were 2 members of CMP #5. the told us that a GEC and an EGC are separate conductors and not to have one conductor provide both uses. I believe there is wording in the 2011 proposals that has been accepted in regards to this.
Show me where it actually says that in the current code. ;)

Additionally the proposal you refer to is regarding not using an EGC as a GEC. There is no proposal that says you can't use a GEC as an EGC. I fail to see a purpose in running an additional grounding conductor. They end up connected together at both ends anyway. But I guess the NEC's position has always been one of overkill. :roll:

Note local bonding is required if available. So running the GEC with the power conductors is only an alternative to running one separately outside the feeder conduit when there are no local electrodes immediately present at the remote location of the SDS.
 

kacper

Member
Location
Islamorada
Show me where it actually says that in the current code. ;)

Additionally the proposal you refer to is regarding not using an EGC as a GEC. There is no proposal that says you can't use a GEC as an EGC. I fail to see a purpose in running an additional grounding conductor. They end up connected together at both ends anyway. But I guess the NEC's position has always been one of overkill. :roll:

Note local bonding is required if available. So running the GEC with the power conductors is only an alternative to running one separately outside the feeder conduit when there are no local electrodes immediately present at the remote location of the SDS.

Frank from Arizona is corrected with the answer, as far NEC the details are in section 250.30

II. System Grounding
250.20(B)(3)
Alternating-Current Systems to Be Grounded.
(3) Where the system is 3-phase, 4-wire, delta connected in
which the midpoint of one phase winding is used as a
circuit conductor
(D) Separately Derived Systems. Separately derived systems,
as covered in 250.20(B), shall be grounded as
specified in 250.30(A). Where an alternate source such as
an on-site generator is provided with transfer equipment
that includes a grounded conductor that is not solidly interconnected
to the service-supplied grounded conductor, the
alternate source (derived system) shall be grounded in accordance
with 250.30(A).

Thank you:)
 

Smart $

Esteemed Member
Location
Ohio
...as far NEC the details are in section 250.30

...
Yes... that would be the next step. Thereafter, please refer to 250.30(A)(5) and (7), then 250.64(A), (B), (C), and (E), plus 250.52(A)... if you wish to continue this conversation.
 

kacper

Member
Location
Islamorada
Yes... that would be the next step. Thereafter, please refer to 250.30(A)(5) and (7), then 250.64(A), (B), (C), and (E), plus 250.52(A)... if you wish to continue this conversation.

250.52 specify the types of grounding electrodes permitted
(A) Electrodes Permitted for Grounding.
(1) Metal Underground Water Pipe. A metal underground
water pipe in direct contact with the earth for 3.0 m (10 ft) or more (including any metal well casing bonded to the pipe) and electrically continuous (or made electrically continuous by bonding around insulating joints or insulating pipe) to the points of connection of the grounding electrode
conductor and the bonding conductors. Interior metal water piping located more than 1.52 m (5 ft) from the point of entrance to the building shall not be used as a part of the grounding electrode system or as a conductor to interconnect electrodes that are part of the grounding electrode system.
(2) Metal Frame of the Building or Structure. ? (You will have to have a proof to verify methods 1,2,3, & 4 Sometimes is not easy on existing buildings)
(3) Concrete-Encased Electrode. - (Need proof on existing buildings)
(4) Ground Ring.
(5)(a)(b) Rod and Pipe Electrodes. ? (Best know method ?Inspector will not argue)
(6) Other Listed Electrodes.
(7) Plate Electrodes.

250.64 (A),(B),(C) is strictly related to method of installation of grounding electrode system itself.

The request u typed was: ?Show me where it actually says that in the current code.?
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Possible "learning moment" for an "ole dog".......
This "contest" and reading 250.30(A)(7) for the millionth time has brought a question to my mind. I have always thought on a SDS to use the closest available water line and building steel as the grounding electrode.
However the specific wording is:
(7) Grounding Electrode. The grounding electrode shall be as near as practicable to and preferably in the same area as the grounding electrode conductor connection to the system. The grounding electrode shall be the nearest one of the following:
(1) Metal water pipe grounding electrode as specified in 250.52(A)(1)
(2) Structural metal grounding electrode as specified in 250.52(A)(2)

(emphasis added)
250.52(A)(1) states the metallic water line beyond the initial 5 ft is not to be considered a grounding electrode.
The commentary to the handbook seems to support the argument that
the GEC must be connected within the 1st 5 ft. of water line.
Does this mean, that if effectively grounded structural steel is not available and the premises does have a water grounding electrode, then the SDS GEC should run back to the water line (withing the 1st 5 ft) regardless of the distance ??

Secondly, without regard to the 2011 proposal, does the Code allow you to use the primary EGC, if sufficient is size, to provide the path back to the water line {assuming any metallic conduits are bonded per 250.64(E)} ?
 

kacper

Member
Location
Islamorada
Possible "learning moment" for an "ole dog".......
This "contest" and reading 250.30(A)(7) for the millionth time has brought a question to my mind. I have always thought on a SDS to use the closest available water line and building steel as the grounding electrode.
However the specific wording is:
(7) Grounding Electrode. The grounding electrode shall be as near as practicable to and preferably in the same area as the grounding electrode conductor connection to the system. The grounding electrode shall be the nearest one of the following:
(1) Metal water pipe grounding electrode as specified in 250.52(A)(1)
(2) Structural metal grounding electrode as specified in 250.52(A)(2)

(emphasis added)
250.52(A)(1) states the metallic water line beyond the initial 5 ft is not to be considered a grounding electrode.
The commentary to the handbook seems to support the argument that
the GEC must be connected within the 1st 5 ft. of water line.
Does this mean, that if effectively grounded structural steel is not available and the premises does have a water grounding electrode, then the SDS GEC should run back to the water line (withing the 1st 5 ft) regardless of the distance ??

Secondly, without regard to the 2011 proposal, does the Code allow you to use the primary EGC, if sufficient is size, to provide the path back to the water line {assuming any metallic conduits are bonded per 250.64(E)} ?

?Does this mean, that if effectively grounded structural steel is not available and the premises does have a water grounding electrode, then the SDS GEC should run back to the water line (withing the 1st 5 ft) regardless of the distance ??? - I think not

All that should be done is to bond the water pipe of the premises at the location accessible for inspection ? eg? water heater location

After entering the building water line is divided to two separated systems (use of different types of fittings compounds and Teflon tapes (fittings to water heaters, faucets ? a lot of them made by plastic) can caused a disconnecting in continuity of the connection.
I think this may also answer the question # 2
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I thought not also, until I closely read 250.30 in regard to the earlier post and then when I checked the Handbook (1st time in years for this section) I found:
effectively grounded metal water pipe is available nearby, 250.30(A)(7) requires that it be used as the grounding electrode. For example, where a transformer is installed on the fiftieth floor, the grounding electrode conductor is not required to be run to the service grounding electrode system. However, where an effectively grounded metal water pipe is used as an electrode for a separately derived system, 250.52(A) specifies that only the first 5 ft of water piping entering the building be used as a grounding electrode. Therefore, the grounding electrode conductor connection to the metal water piping must be made at some point on this first 5 ft of piping.
I recognize Handbook commentary is not "Code" , but apparently some folks think differently from my 1st thoughts and yours.
 

Smart $

Esteemed Member
Location
Ohio
.... Interior metal water piping located more than 1.52 m (5 ft) from the point of entrance to the building shall not be used as a part of the grounding electrode system or as a conductor to interconnect electrodes that are part of the grounding electrode system.
...

The request u typed was: “Show me where it actually says that in the current code.”
Underline in quote by me.

I do not see how what you bolded relates to my question. :confused:

An enhanced form of my question is: Show me in the current code where it says a single conductor shall not serve as both an EGC and a GEC.
 

Smart $

Esteemed Member
Location
Ohio
...

Does this mean, that if effectively grounded structural steel is not available and the premises does have a water grounding electrode, then the SDS GEC should run back to the water line (withing the 1st 5 ft) regardless of the distance ??
Yes.

Secondly, without regard to the 2011 proposal, does the Code allow you to use the primary EGC, if sufficient is size, to provide the path back to the water line {assuming any metallic conduits are bonded per 250.64(E)} ?
The NEC up to this point does not prohibit such.
 

Smart $

Esteemed Member
Location
Ohio
?Does this mean, that if effectively grounded structural steel is not available and the premises does have a water grounding electrode, then the SDS GEC should run back to the water line (withing the 1st 5 ft) regardless of the distance ??? - I think not

All that should be done is to bond the water pipe of the premises at the location accessible for inspection ? eg? water heater location

After entering the building water line is divided to two separated systems (use of different types of fittings compounds and Teflon tapes (fittings to water heaters, faucets ? a lot of them made by plastic) can caused a disconnecting in continuity of the connection.
I think this may also answer the question # 2

I thought not also, until I closely read 250.30 in regard to the earlier post and then when I checked the Handbook (1st time in years for this section) I found:
effectively grounded metal water pipe is available nearby, 250.30(A)(7) requires that it be used as the grounding electrode. For example, where a transformer is installed on the fiftieth floor, the grounding electrode conductor is not required to be run to the service grounding electrode system. However, where an effectively grounded metal water pipe is used as an electrode for a separately derived system, 250.52(A) specifies that only the first 5 ft of water piping entering the building be used as a grounding electrode. Therefore, the grounding electrode conductor connection to the metal water piping must be made at some point on this first 5 ft of piping.
I recognize Handbook commentary is not "Code" , but apparently some folks think differently from my 1st thoughts and yours.
Bonding to local metal piping system(s) does not qualify as a GES.
 

kacper

Member
Location
Islamorada
Underline in quote by me.

I do not see how what you bolded relates to my question. :confused:

An enhanced form of my question is: Show me in the current code where it says a single conductor shall not serve as both an EGC and a GEC.

"I do not see how what you bolded relates to my question."

Question u posted: ?Show me where it actually says that in the current code.?

My answer :
?Frank from Arizona is corrected with the answer, as far NEC the details are in section 250.30

II. System Grounding
250.20(B)(3)
Alternating-Current Systems to Be Grounded.
(3) Where the system is 3-phase, 4-wire, delta connected in
which the midpoint of one phase winding is used as a
circuit conductor
(D) Separately Derived Systems. Separately derived systems,
as covered in 250.20(B), shall be grounded as
specified in 250.30(A). Where an alternate source such as
an on-site generator is provided with transfer equipment
that includes a grounded conductor that is not solidly interconnected
to the service-supplied grounded conductor, the
alternate source (derived system) shall be grounded in accordance
with 250.30(A).?
 

M. D.

Senior Member
Well, I found this I hope it helps

Report on Proposals ? May 2004 NFPA 70
5-99 Log #2716 NEC-P05
(250-30(A)(4) Exception No. 2 (New) ) Final Action: Reject
Submitter: Donald A. Ganiere Ottawa, IL
Recommendation:
Renumber existing Exception as Exception No. 1 and add new Exception No. 2 as follows:
"Exception No. 2: Where a transformer is used as a separately derived system and where the transformer primary feeder circuit
originates in the same building or structure, a grounding electrode shall not be required."
Substantiation:
There is no electrical or safety related reason to require a grounding electrode for a transformer used as a separately derived system when
the primary power source for the transformer is located in the same building or structure. The requirements of 250.4(A)(1) are met
without the use of a grounding electrode at the secondary side of the transformer. Lighting is not a problem within the building or
structure. The only possible contact with a higher voltage system is a fault on the primary feeder and this fault will be cleared by the
primary feeder equipment grounding conductor. The bonding required by 250.30(A)(1) will stabilize the voltage to earth under normal
operating conditions. The same bonding in combination with the primary feeder equipment grounding conductor will limit the effect of
line surges. The addition of a direct connection from the secondary side of a separately derived system to a grounding electrode
provides no additional protection over that which is already provided by the primary feeder equipment grounding conductor.
Panel Meeting Action: Reject
Panel Statement:
The present requirements for separately derived systems to be grounded to a reference earth by a dedicated grounding electrode
conductor apply to all systems without regard of installation inside or outside the building or structure served. The primary reason is to
establish an earth ground reference and stabilize the system voltage around this reference. The equipment grounding conductor from the
source to the separately derived system does not meet the requirements for size, not having a choke effect when installed in metal
raceways, multiple terminations, etc. The equipment grounding conductor's primary purpose is to provide a low impedance path for
fault current in the event of a ground-fault on the system up to and including the primary of the transformer, not to act as the low
impedance earth reference conductor.
Number Eligible to Vote: 16
Affirmative: 15 Negative: 1
Ballot Results:
Explanation of Negative:
RAPPAPORT: The purpose of the grounding electrode conductor in the proposed Exception is to stabilize voltage. See my Comment
on Affirmative on Proposal 5-91. An equipment grounding conductor, run with the feeder to the separately derived system and sized for
the separately derived system, should be adequate.

It was a response to questions beaten around back in the time of Bennie one such discussion can be found here

http://forums.mikeholt.com/showthread.php?t=56713&page=2

I would like to know what you guys think
 

Smart $

Esteemed Member
Location
Ohio
Well, I found this I hope it helps



It was a response to questions beaten around back in the time of Bennie one such discussion can be found here

http://forums.mikeholt.com/showthread.php?t=56713&page=2

I would like to know what you guys think
I'm already on record as to what I think. ;)

The proposal cited is to relinquish the SDS GES requirement altogether for an SDS in the same structure as the service. I could have guessed that wouldn't "fly". However, note the Explanation of Negative.
 

M. D.

Senior Member
I guess it is really the same thing as you suggest with the idea of an equipment electrode conductor ,..isn't it ??

The only reason to have a grounding electrode conductor is the grounding electrode ,.. yes??

Anyway Don seems to have thought so (from the link)

in response to Bennie asking why the transformer needs a grounding electrode

Bennie,
That is a very good question. I have submitted a proposal that would permit the primary EGC to also serve as the transformer secondary GEC where both the service disconnect and the transformer are located in the same building.
Don
______________
 

Smart $

Esteemed Member
Location
Ohio
I guess it is really the same thing as you suggest with the idea of an equipment electrode conductor ,..isn't it ??

The only reason to have a grounding electrode conductor is the grounding electrode ,.. yes??

Anyway Don seems to have thought so (from the link)

in response to Bennie asking why the transformer needs a grounding electrode


______________

Yes... Yes. I'm a yes man (when I'm not a no man :D)
 
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