Do I need a 4 pole ATS?

[Mvillines]

Guys, my point to quoting 250.142 is a technical point.

I agree that the transformer is wired in Smart$'s drawing exactly like a non SDS generator and i agree we could call it a non seperately derived transformer.

Article 250.35 gives us permission to wire generators as non seperately derived systems. There is not a single article that gives us permission to wire transformers as non seperately derived systems.

Article 250.142 gives us permission to use the grounded conductor in the following manner...

A grounded circuit conductor shall be permitted to ground non?current-carrying metal parts of equipment, raceways, and other enclosures at any of the following locations:

(1) On the supply side or within the enclosure of the ac service-disconnecting means
(2) On the supply side or within the enclosure of the main disconnecting means for separate buildings as provided in 250.32(B)
(3) On the supply side or within the enclosure of the main disconnecting means or overcurrent devices of a separately derived system where permitted by 250.30(A)(1)

Since this transformer is not a SDS and it does not fit any of the 3 listed locations and is not a generator, the grounded conductor does not have permission to be used to "ground non?current-carrying metal parts of equipment, raceways, and other enclosures"
My technical point is untill permission is granted, this install is unsat.

Rick

RUWired I now understand your point and a very good point at that. As I said before....I have to study on this one.

 

[Smart $]

I could be reading this wrong, but I don't think the transformer is part of the service system. The service stops at the first disconnect from the serving utility. Re-read the definition for feeders.

I didn't say it was part of the service, I said [or meant it to say] it was part of the service-[supplied-]system. A seperately derived system has no current-carrying conductors in common with a service-supplied-system.

 

[Smart $]

Guys, my point to quoting 250.142 is a technical point.

I agree that the transformer is wired in Smart$'s drawing exactly like a non SDS generator and i agree we could call it a non seperately derived transformer.

Yeah, yeah...

Article 250.35 gives us permission to wire generators as non seperately derived systems. There is not a single article that gives us permission to wire transformers as non seperately derived systems.

...and conversely, there is no article which says it is not permissable.

Article 250.142 gives us permission to use the grounded conductor in the following manner...

A grounded circuit conductor shall be permitted to ground non–current-carrying metal parts of equipment, raceways, and other enclosures at any of the following locations:

(1) On the supply side or within the enclosure of the ac service-disconnecting means
(2) On the supply side or within the enclosure of the main disconnecting means for separate buildings as provided in 250.32(B)
(3) On the supply side or within the enclosure of the main disconnecting means or overcurrent devices of a separately derived system where permitted by 250.30(A)(1)

Since this transformer is not a SDS and it does not fit any of the 3 listed locations and is not a generator, the grounded conductor does not have permission to be used to "ground non–current-carrying metal parts of equipment, raceways, and other enclosures"
My technical point is untill permission is granted, this install is unsat.

Once again, we are not using the grounded conductor for grounding of any non-current-carrying metallic parts. Non-current-carrying metallic parts of the equipment under discussion are grounded by way of both the GES's and their interconnected EGC's. 250.142 in its entirety does not apply... period!

 

[RUWired]

Once again, we are not using the grounded conductor for grounding of any non-current-carrying metallic parts. Non-current-carrying metallic parts of the equipment under discussion are grounded by way of both the GES's and their interconnected EGC's. 250.142 in its entirety does not apply... period!

I just don't see it that way. Take away the grounded conductor and tell me how the OCPD will trip if your only using the EGC. I can't get past that point.

The grounded conductor is being used back at the service and at each unit with SDS transformers and generators to ground the equipment and in those three location, it is allowed.

Without the neutral being grounded, the EGC has no use. So you can't say the Neutral is not being used to ground.

I might add...250.142 Use of Grounded Circuit Conductor for "Grounding" Equipment.

Rick

 

[Smart $]

...So you can't say the Neutral is not being used to ground.

It is being used to GROUND the alternate AC power source... but it is not being used to ground non-current-carrying metal parts.

The title of 250.142 is "Use of a Grounded Circuit Conductor for Grounding Equipment". "Grounding Equipment" means the grounding of non-current-carrying metal parts of equipment NOT the current-carrying parts or conductors interconnecting those parts.

The grounded circuit conductor you are referring to is part of the fault-current path, but it is no different than the service grounded circuit conductor being part of the fault-current path. And just because it is part of the fault-current path does not mean it is being used for GROUNDING non-current-carrying metal parts of equipment.

What if you wired the transformer as an SDS and put the bonding jumper at the secondary's disconnect instead of at X0. The grounded circuit conductor between the transformer and its disconnect in this wiring configuration serves the same purpose as the one you are trying to say is disallowed.

 

[RUWired]

Smart$, did you read up on article 450.6 and 6(C) and what do you think besides I don't think i applies. The transfer switch can be considered the secondary tie especially if the feeder supplying the xfer sw is right off the main service panel.

450.6 Secondary Ties.
As used in this article, a secondary tie is a circuit operating at 600 volts, nominal, or less between phases that connects two power sources or power supply points, such as the secondaries of two transformers. The tie shall be permitted to consist of one or more conductors per phase or neutral. Conductors connecting the secondaries of transformers in accordance with 450.7 shall not be considered secondary ties.

 

[RUWired]

What if you wired the transformer as an SDS and put the bonding jumper at the secondary's disconnect instead of at X0. The grounded circuit conductor between the transformer and its disconnect in this wiring configuration serves the same purpose as the one you are trying to say is disallowed.

Article 250.142(3) allows this...


(3) On the supply side or within the enclosure of the main disconnecting means or overcurrent devices of a separately derived system where permitted by 250.30(A)(1)

 

[Pierre C Belarge]

Okay, I have tried to keep up with this thread, it is not easy to do.
My comments are based on the illustrations presented, if you do not mind.


1. Transformers may or may not be SEPARATELY DERIVED SYSTEMS (SDS).
Auto-transformers share windings and may not be SDS. Most other transformers do not share "circuit conductors" therefore they are classified as SDS. Equipment ground conductors are not "circuit conductors".
[the transformer as shown in the illustration is, from what has been described, a SDS]

2. The generator in this installation is somewhat unusual and not normally seen installed in this location. Why was a generator of the necessary voltage not provided to start with?

3. The secondary side of the transformer and the first disconnect on the secondary side do not show where the "grounded conductor" is grounded. It should either be in the transformer...or the first means of disconnect. 250.30(A)(1)

4. The transfer switch is what determines if a generator is a separately derived system. Since the generator is on the primary side of the tranformer in regards to the "standby" side of the transfer switch, I would say the ATS has no bearing on the generator. It has bearing on the "standby system".

5. Since this system is 208y/120 and there is no GFP protection, I do not see the need for a 4 pole ATS. It certainly could be installed, but is not required.

6. Generators are as per definitions separate structures. The NEC 250.32 requires separate structures that are supplied from... to have a grounding electrode system as per 250.50 to be installed.
Generators are not supplied from the building, they do the supplying. A grounding electrode system is not required. A ground rod is usually supplied as per the manufacturer's installation instructions...for lightning protection.




I may have missed some of the details, this is a very long and detailed thread. Hopefully it is not something that affects my answer...if it does, I am sure you will all let me know. :grin:

 

[Smart $]

Article 250.142(3) allows this...


(3) On the supply side or within the enclosure of the main disconnecting means or overcurrent devices of a separately derived system where permitted by 250.30(A)(1)

You keep bringing up 250.142, yet it has no bearing on this connection or conductor. However I'll go along for the moment...

Simple fact... connected as per diagrammed, the transformer is not an SDS. Therefore no article or subpart therein pertaining to an SDS applies to this transformer. Where is the grounding taking place in my diagram that you are saying is disallowed? As I see it the GROUNDING is taking place at the Service Disconnecting Means, which is permitted under 250.142.

I don't know what else I can say to help you see the installation as diagrammed is compliant...

...and if by chance I am wrong, I will gladly admit it... but I've yet to hear, see, or read any irrefutable evidence contrary to my belief.

 

[Pierre C Belarge]

Article 100

Separately Derived System
A premises wiring system whose power is derived from a source of electric energy or equipment other than a service. Such systems have no direct electrical connections, including a solidly connected grounded circuit conductor, to supply conductors originating in another sytem.


The transformer in the illustration does not have any connected "circuit conductors" connected together. Remember that the EGC is not a circuit conductor.

It is rare that a power transformer installed in our field would not be a separately derived system.

 

[Mvillines]

Article 250.142(3) allows this...


(3) On the supply side or within the enclosure of the main disconnecting means or overcurrent devices of a separately derived system where permitted by 250.30(A)(1)

250.142 (A) and (B) is describing the grounded conductor as serving a dual purpose, grounded and grounding function. The intent is to prevent normal current form flowing over the EGC in the event the grounded conductor becomes interrupted. Referring to diagram, an open grounded conductor would totally interrupt the current flow and not allow the normal current to take an alternate route over the EGC or any other metal parallel paths. This is a single point grounding and bonding system.

 

[Mvillines]

Article 100

Separately Derived System
A premises wiring system whose power is derived from a source of electric energy or equipment other than a service. Such systems have no direct electrical connections, including a solidly connected grounded circuit conductor, to supply conductors originating in another sytem.


The transformer in the illustration does not have any connected "circuit conductors" connected together. Remember that the EGC is not a circuit conductor.

It is rare that a power transformer installed in our field would not be a separately derived system.

Rare?? Before this thread I would have said all power transformers would be SDS (excluding autoxformers). This transformer as shown is not a SDS, the grounded conductor is a circuit conductor and has a solid connection with the service neutral and grounding electrode system.

I still say this is a valid and compliant system.

 

[Smart $]

Article 100

Separately Derived System
A premises wiring system whose power is derived from a source of electric energy or equipment other than a service. Such systems have no direct electrical connections, including a solidly connected grounded circuit conductor, to supply conductors originating in another sytem.


The transformer in the illustration does not have any connected "circuit conductors" connected together. Remember that the EGC is not a circuit conductor.

It is rare that a power transformer installed in our field would not be a separately derived system.

The grounded circuit conductor of the transformer is solidly connected to the service-supplied feeder's grounded circuit conductor.

As a side note, there are no parallel neutral (grounded conductor) current paths. Do you know of any way to ground the transformer's output without creating a parallel neutral current path (and without using a 4-pole ATS)?

 

[Smart $]

Smart$, did you read up on article 450.6 and 6(C) and what do you think besides I don't think i applies. The transfer switch can be considered the secondary tie especially if the feeder supplying the xfer sw is right off the main service panel.

450.6 Secondary Ties.
As used in this article, a secondary tie is a circuit operating at 600 volts, nominal, or less between phases that connects two power sources or power supply points, such as the secondaries of two transformers. The tie shall be permitted to consist of one or more conductors per phase or neutral. Conductors connecting the secondaries of transformers in accordance with 450.7 shall not be considered secondary ties.

Yes, I'm up to speed on 450.6(C). It is one of those special instances where creating a parallel neutral path via the grounding system is allowed. While it makes your point, it unfortunately does not apply.

 

[qcroanoke]

Okay, I have tried to keep up with this thread, it is not easy to do.
My comments are based on the illustrations presented, if you do not mind.


2. The generator in this installation is somewhat unusual and not normally seen installed in this location. Why was a generator of the necessary voltage not provided to start with?




I may have missed some of the details, this is a very long and detailed thread. Hopefully it is not something that affects my answer...if it does, I am sure you will all let me know. :grin:

The generator also is supplying some delta loads with the 400 amp output breaker. So the correct generator was supplied.
The reason for the delta/wye xfmr is to supply 120/208 3 phase loads in our building from the 200 amp delta output of the generator.
As I posted earlier the generator has 2 output breakers 1-400 for the delta loads And 1-200 to feed the xfmr.

 

[Pierre C Belarge]

Rare?? Before this thread I would have said all power transformers would be SDS (excluding autoxformers). This transformer as shown is not a SDS, the grounded conductor is a circuit conductor and has a solid connection with the service neutral and grounding electrode system.

I still say this is a valid and compliant system.

Read my post again, that is what I said.


The transformer shown is a SDS. It is not the connection to the panel that determines this, it is the wiring within the transformer itself. There is no neutral connection from the primary to the secondary, hence the transformer is a SDS.

 

[Pierre C Belarge]

The grounded circuit conductor of the transformer is solidly connected to the service-supplied feeder's grounded circuit conductor.

As a side note, there are no parallel neutral (grounded conductor) current paths. Do you know of any way to ground the transformer's output without creating a parallel neutral current path (and without using a 4-pole ATS)?

Take a grounding electrode conductor sized as per 250.66 to one of the two electrodes mentioned in 250.30(A)(7). That will not create a parallel path.

 

[Smart $]

Take a grounding electrode conductor sized as per 250.66 to one of the two electrodes mentioned in 250.30(A)(7). That will not create a parallel path.

That would work... but conditional:

1. If connected to X0 only (i.e. no connection to otherwise grounded non-current-carrying metal parts), and...
2. As long as either of those electrodes wasn't the same electrode as used for the GES of the service.

On the latter, I'm leaning on the doubtful side of that possibility.

PS: I didn't think of it earlier, but if this is an outside transformer, it will require an ground rod and GEC bonded to X0.

 

[Mvillines]

What reference are you using? If 250.24 Grounding Service-Supplied Alternating-Current Systems. Remember this is not a service but feeders.

As for connecting the transformer XO terminal to a separate grounding electrode is a very bad idea. 250.24 (A)(5) prohibits this unless otherwise permitted and I not sure there are other permission in this case. 250.4(A)(5), (B)(4), and 250.54 indicates that the earth is a current path just not an effective path which could create a dangerous condition if the grounded conductor were to open. Would this violate 250.6?

250.54 allows supplementary grounding electrodes to be connected to the equipment grounding conductors not the grounded conductor. If the transformer is outside, this would probably be a good idea. To the case ground only not the XO terminal.

 

[Smart $]

What reference are you using? If 250.24 Grounding Service-Supplied Alternating-Current Systems. Remember this is not a service but feeders.

As for connecting the transformer XO terminal to a separate grounding electrode is a very bad idea. 250.24 (A)(5) prohibits this unless otherwise permitted and I not sure there are other permission in this case. 250.4(A)(5), (B)(4), and 250.54 indicates that the earth is a current path just not an effective path which could create a dangerous condition if the grounded conductor were to open. Would this violate 250.6?

250.54 allows supplementary grounding electrodes to be connected to the equipment grounding conductors not the grounded conductor. If the transformer is outside, this would probably be a good idea. To the case ground only not the XO terminal.

As to the ground rod and GEC at outside transformer, I was in error on that one. I was thinking (without confirming ) of 250.24(A)(2)... but that is in regards only to an outside transformer supplying the service.

As for adding any electrode, I am in agreement... I was just trying to appease Pierre's comment... and we see what that got me. Every time I try to configure the system other than what I drew up, it comes back to bite me. This is what I get for trying to accomodate others belief that my configuration is wrong