1200A Main grounding conductor

[JEMENG]

I need to size the grounded conductor between the 480V side of a utility transformer and the customer's service entrance equipment (1200A breaker) on a 750kW PV system (only PV, no significant loads).

I've been told that this should be treated as a feeder with a 1200A overcurrent protection due to the PV inverters (w/ 3/o EGC and 3/o neutral) per 250.122. However, it also seems to fit under a service entrance sizing from 250.66 which would put the grounded conductor at a 1/o (600kcmil per conduit).

Should this be treated as a service entrance or a feeder?

 

[augie47]

IMO, PV or not, between the utility transformer and the disconnect is "service" and the grounded conductor should be sized for the load with a minimum as required by 250.66

 

[Smart $]

Service entrance conductors.

If ungrounded conductors in parallel conduits are 600kcmil, your minimum size will be 2/0 (assuming copper).

 

[texie]

Service entrance conductors.

If ungrounded conductors in parallel conduits are 600kcmil, your minimum size will be 2/0 (assuming copper).

1/0.

 

[Smart $]

1/0.

My bad. Looked at the size numbers and mentally ignored the "Over" and "through". :ashamed1:

 

[texie]

My bad. Looked at the size numbers and mentally ignored the "Over" and "through". :ashamed1:

You know how it is around here. One little slip, looking at the wrong line, etc. we pounce like prosecution lawyers.
One of those deals like larger than #6 or #4 and larger.

 

[GoldDigger]

You know how it is around here. One little slip, looking at the wrong line, etc. we pounce like prosecution lawyers.
One of those deals like larger than #6 or #4 and larger.

There is no #5, right?
(...and God created the even numbers and they were good.)

 

[Smart $]

There is no #5, right?
(...and God created the even numbers and they were good.)

I believe #5 exists as an original wire size specification of the American Wire Gauge. But I've never seen it commercially available.

 

[augie47]

Actually there are some high voltage cables with concentric neutrals that use
"odd" sizes like 5 & 7.

 

[JEMENG]

Thanks for the response.

If it were a customer owned transformer, would it be treated as a separately derived system (and size grounded conductor via 250.66) rather than a feeder (and 250.122)?

 

[augie47]

Basic rule: If it is directly protected by an over-current device ahead of the associated conductors, 250.122;
if not 250.66

 

[JEMENG]

So in this case, the breaker is ahead of the conductor as seen by the PV source, but behind the conductor as seen by the utility source. Should it be done for the worst case of either....which would end up as 250.122

The PV inverters typically don't have enough fault current to trip the device (short circuit is only ~115% of load current), but I can see the argument that it is the feed to the transformer.

 

[Smart $]

So in this case, the breaker is ahead of the conductor as seen by the PV source, but behind the conductor as seen by the utility source. Should it be done for the worst case of either....which would end up as 250.122

The PV inverters typically don't have enough fault current to trip the device (short circuit is only ~115% of load current), but I can see the argument that it is the feed to the transformer.

On the PV side, it depends on whether the grounding conductor is shared GEC/EGC or just EGC.

On the transformer side, it depends on whether these are service conductors or transformer secondary conductors of a separately derived system. Ownership of transformer is not an absolute method of determining which. If service, and a grounded system, no grounding conductor is required. All grounding is done by bonding to grounded conductor. Not certain about ungrounded service, but probably same as SDS... I believe you use 250.66 (your under 2008 NEC, right?).

 

[kwired]

On the PV side, it depends on whether the grounding conductor is shared GEC/EGC or just EGC.

On the transformer side, it depends on whether these are service conductors or transformer secondary conductors of a separately derived system. Ownership of transformer is not an absolute method of determining which. If service, and a grounded system, no grounding conductor is required. All grounding is done by bonding to grounded conductor. Not certain about ungrounded service, but probably same as SDS... I believe you use 250.66 (your under 2008 NEC, right?).

Ownership no, location in relation to "service point" yes.

 

[Smart $]

Ownership no, location in relation to "service point" yes.

Since you brought it up, you explain...

 

[kwired]

Since you brought it up, you explain...

Alright - the art 100 definition of Service point along with the informational note that follows explains most of it, so I will quote those:

Service Point.
The point of connection between the facilities of the serving utility and the premises wiring.


Informational Note: The service point can be described as the point of demarcation between where the serving utility ends and the premises wiring begins. The serving utility generally specifies the location of the service point based on the conditions of service.

For the most part if something is on the supply side of service point NEC doesn't apply, if it is on the load side of the service point NEC does apply. So with a transformer - if the service point is on the load side NEC doesn't apply and the secondary conductors are service conductors until they hit a service disconnecting means - which should be on load side of the service point, or maybe the disconnect is designated as the service point.

Keep in mind this term was added to NEC in 2011 (I think, could have been 2008). It was an attempt, and was fairly successful attempt to clarify just what NEC applies to and what is under control of the POCO and doesn't apply to NEC. Ownership is not necessarily the main criteria for determining the service point, but often utility does own supply side equipment. Sometimes though a utility does require the customer to provide some equipment even though the utility does more less acquire and maintain that equipment after initial installation, but supply side of service point is not subject to NEC even if owner or his contractor installs it.

 

[Smart $]

Alright - the art 100 definition of Service point along with the informational note that follows explains most of it, so I will quote those:



For the most part if something is on the supply side of service point NEC doesn't apply, if it is on the load side of the service point NEC does apply. So with a transformer - if the service point is on the load side NEC doesn't apply and the secondary conductors are service conductors until they hit a service disconnecting means - which should be on load side of the service point, or maybe the disconnect is designated as the service point.

Keep in mind this term was added to NEC in 2011 (I think, could have been 2008). It was an attempt, and was fairly successful attempt to clarify just what NEC applies to and what is under control of the POCO and doesn't apply to NEC. Ownership is not necessarily the main criteria for determining the service point, but often utility does own supply side equipment. Sometimes though a utility does require the customer to provide some equipment even though the utility does more less acquire and maintain that equipment after initial installation, but supply side of service point is not subject to NEC even if owner or his contractor installs it.

Okay... so if the service point is the primary terminals of the customer-owned transformer, are the transformer secondary conductors service conductors or not? If not, there has to be a service disconnecting means integral with the transformer so no service conductors conductors leave the transformer enclosure... and no transformers that I have experienced in this role have integral service disconnecting means...???

 

[electrofelon]

Okay... so if the service point is the primary terminals of the customer-owned transformer

I don't see how that could ever be code compliant for several reasons.....

 

[Smart $]

I don't see how that could ever be code compliant for several reasons.....

???

 

[JEMENG]

My specific installation has a 13.2kV disconnect as a service point, then customer owned transformer, (creating the separately derived system) and a 1200A breaker on the 480V side. It is under NEC2008.

Technically the transformer is a step up transformer, as it is being used to get the PV power from 480V up to 13.2kV. Therefore, I have been told that the 480V conductors between the 1200A breaker and the transformer should be treated as a feeder rather than a transformer secondary. Then this would change how the grounded conductors are sized (between 250.66 and 250.120).