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Joined: Mar 2003
Posts: 849
All conductors including the Grounded conductor Must be broken.
480 Volt 3 phase (Transformer mini power center) to 120-208 volt secondary Panel
that feeds pumps & dispensor circuits.
Shunt trip the Primary (480 volt 3 phase) thur Emergency stop button.
Completely Shuts dn Panel feed to 120/208 volt off.
Does this meet the intent of the code?
(Never saw it done this way )??

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Joined: Apr 2002
Posts: 7,299
Likes: 6
I have not seen this method either, seems to meet the intent of 514.11, sort of.

As long as the transformer and panel only kill the dispensers, and not effect any life safety items.

Joined: Mar 2011
Posts: 98

How is that breaking the grounded conductor originating on the 208/120 side of the transformer?

Joined: Mar 2005
Posts: 212
I'm with vindiceptor. Killing the source of the primary does not disconnect the grounded conductor on the secondary side.
514.11(a) also refers to the "source of supply". In a separately derived system that's the secondary coil, not the primary.

Joined: Apr 2002
Posts: 7,299
Likes: 6
We have to debate the word 'breaking' as in the opening of a knife switch, as opposed to 'de-energizing' all conductors.

Yes, there is no physical disconnection of the grounded conductors, but there also is no voltage potential within the fictious panel.

As I said above, "seems to, sort of'. Would I accept this setup IF prsented on a set of PE/EE signed and sealed plans? I cannot say that I would or would not at this time.

Note that in the 2011 this section was modified to:

514.11 Circuit Disconnects.
(A) General. Each circuit leading to or through dispensing
equipment, including all associated power, communications,
data, and video circuits, and equipment for remote pumping
systems, shall be provided with a clearly identified and readily
accessible switch or other approved means, located remote
from the dispensing devices, to disconnect simultaneously
from the source of supply, all conductors of the circuits, including
the grounded conductor, if any.

The wording "or other approved means" IMHO will result with a manufactured control panel that will 'kill' everything within the dispensers.

Joined: Mar 2005
Posts: 212
I don't think we have to debate the word at all. According to the section you posted above, it doesnt matter which method is used to "disconnect simultaneously from the SOURCE OF SUPPLY, all conductors of the circuits, including the grounded conductor, if any." Opening the circuit on the primary side of a transformer does not disconnect the grounded conductor from its source of supply, which is the secondary coil. The fact that there is no voltage potential when the primary is disconnected is not germain to the question.

Joined: Mar 2003
Posts: 849
The Source of the Grounded conductor is on the Load side of the transformer. The Grounded conductor does not exist on XO
till the 120/208 exist. A Grounding conductor existing on the Primary feeder side but NOT a grounded conductor.

Joined: Jul 2004
Posts: 9,696
Likes: 11
I have just been watching since my personal knowledge of gas pumps is selecting the right grade and getting the hose in the filler neck but you do seem to be stuck on whether the SDS is a "source".

Perhaps it would be interesting to find out why it is important to disconnect the grounded conductor in the first place. Has anyone researched the ROP for the origin of this rule?

Greg Fretwell
Joined: Apr 2002
Posts: 7,299
Likes: 6

I believe the reasoning for disconnecting the grounded conductor was required to prevent any possibility of electrical energy to be present within the dispensers.
Hence, the availability of a cb with the facility to 'open' the neutral conductor.


The assured elimination of all electrical energy within the dispenser is, IMHO the intent of 514.11. Both for service and maintenance of the dispenser, via the circuit breaker for the dispenser/item requiring maintenance AND in emergency situations, the EPO which kills ALL power to the fuel islands. We seem to agree on this.

The OP leads me to follow the scenario for the EPO, which, again IMHO should be compliant via the termination of the transformer primary. This method must not affect any life safety items when the EPO is activated.

Joined: Jun 2004
Posts: 1,273
The grounded conduct can become energized at voltages above the local 'equal potential' plane --

As a result of collision/ accident / fire in the transformer windings.

Amazing things happen in collapsing transformer fields.

In normal circumstances grounded conductors are no problem -- EPO's exist because vehicles are known colliders.

Over the years, fire departments have seen every manner of troubles when transformers are destroyed by collisions/ earthquakes / tsunamis....

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