1200A Main grounding conductor

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augie47

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Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Think about many universities and industrial complexes.
Customer may well own the transformers, often they even own the primary transmission line. The transformers are SDS systems and the transformer conductors fall under 240.21(C).
The biggest change might be the fact that the conductors to the building are now sized by the NEC. the transformer disconnect might well be a pole mounted switch.
(There is a bit of controversy concerning 250.30 Exception 2, with some changes ion the '11 Code but thats another subject)
 
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kwired

Electron manager
Location
NE Nebraska
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...???
Somehow you need to sneak a service disconnecting means in that installation if the service point is on the primary side of the transformer.

The AHJ needs to step in and say it is not possible to make the input terminals the service point, POCO apparently intends the service point to be on supply side - but to meet code it needs a service disconnecting means.

JMO.
 

iwire

Moderator
Staff member
Location
Massachusetts
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...???

No can do.

For starters check out 230.82

I could probably come up with more but I am out tent camping with family. :)
 

kwired

Electron manager
Location
NE Nebraska
Think about many universities and industrial complexes.
Customer may well own the transformers, often they even own the primary transmission line. The transformers are SDS systems and the transformer conductors fall under 240.21(C).
The biggest change might be the fact that the conductors to the building are now sized by the NEC. the transformer disconnect might well be a pole mounted switch.
(There is a bit of controversy concerning 250.30 Exception 2, with some changes ion the '11 Code but thats another subject)
Again ownership doesn't necessarily determine service point. I think a lot of POCO's charge customers for equipment and consider the customer to be the owner of that equipment - yet POCO installs and maintains it, whether it be a meter socket, service drop or lateral, or even a section of primary distribution line.
 

augie47

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Location
Tennessee
Occupation
State Electrical Inspector (Retired)
As kwired notes,I don't know that ownership of the transformer or other equipment would make a difference one way or the other...that's a contractual agreement.
The service point would be decided on by the customer/utility. If the service point is the transformer secondary, regardless of ownership, then the service conductors would be customer supplied but that would not change any Art 230 rules.
If the service point is on the primary side then Art 230 Part VIII, and Art 225 Part III come into play and there is a whole lot more latitude on the service disconnect means including location, size, etc.
We have a number of facilities in this area with customer owned distribution.
 
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I was thinking primary transformer protection required, and 230.82 (equipment allowed on supply side of service disconnect).

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).

Unless I have missed it, I dont see any language in the code that changes the classification of conductors based on whether there is interactive PV or the equipment is for the sole purpose of PV.
 

GoldDigger

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Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Are you trying to make a distinction based on whether or not there are also local loads?
IMHO any GTI is by design utility interactive whether there are local loads or not. And in any case, some control and monitoring loads will always exist even when the PV input circuit is inactive.
 
Are you trying to make a distinction based on whether or not there are also local loads?
IMHO any GTI is by design utility interactive whether there are local loads or not. And in any case, some control and monitoring loads will always exist even when the PV input circuit is inactive.

Yeah it's sort of tempting to think about things differently if the entire service is just for the GTI, and the code doesn't define primary and secondary of a transformer so the argument could be made...i personally don't subscribe to that philosophy though.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
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).

If it is part of the premises wiring, then a transformer secondary is a feeder according to the NEC, so there is no 'rather than' there to consider. I also agree with...

Unless I have missed it, I dont see any language in the code that changes the classification of conductors based on whether there is interactive PV or the equipment is for the sole purpose of PV.

The sizing of grounded conductors and EGCs (whichever applies in this case) is based on fault current from the utility side and the presence of PV shouldn't and doesn't (IMO) change that.
 
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Smart $

Esteemed Member
Location
Ohio
If it is part of the premises wiring, then a transformer secondary is a feeder according to the NEC, so there is no 'rather than' there to consider. I also agree with...



The sizing of grounded conductors and EGCs (whichever applies in this case) is based on fault current from the utility side and the presence of PV shouldn't and doesn't (IMO) change that.
Agree. I actually had something similar in progress and had to leave for awhile. Figured I'd check for updated post before submitting and there it was... ;)

In short, grounding conductor between transformer secondary and disconnecting means is sized per Table 250.66.
 

kwired

Electron manager
Location
NE Nebraska
If it is part of the premises wiring, then a transformer secondary is a feeder according to the NEC, so there is no 'rather than' there to consider. I also agree with...

If the transformer is part of premises wiring NEC applies and 450.3 does require overcurrent protection.

If only the secondary is considered premises wiring (not sure if that happens or not) it is not a feeder unless it is a two wire secondary or a three wire delta and overcurrent is provided on the primary at the primary to secondary ratio. Therefore if not protected properly it has to be either a service conductor or a feeder tap, to be a feeder it must have proper overcurrent protection on supply side of the conductor.
 

Smart $

Esteemed Member
Location
Ohio
If the transformer is part of premises wiring NEC applies and 450.3 does require overcurrent protection.

If only the secondary is considered premises wiring (not sure if that happens or not) it is not a feeder unless it is a two wire secondary or a three wire delta and overcurrent is provided on the primary at the primary to secondary ratio. Therefore if not protected properly it has to be either a service conductor or a feeder tap, to be a feeder it must have proper overcurrent protection on supply side of the conductor.
OP'er said there's a disconnect on the 13.2V primary side of non-POCO transformer (http://forums.mikeholt.com/showthread.php?t=163745&p=1590494#post1590494), but no mention of OCPD... so we're left assuming OCPD is provided on primary (with the xfmr being non-POCO and y'alls comments related to service point ;)).

Anyway, still a feeder, but atypical by definition. It'd be an Interconnected Electric Power
Production Sources feeder, for lack of a better description. This is plainly evident with 705.12(D) revisions of the 2014 NEC edition.

OP'er also did not mention whether secondary is delta or wye configured, or grounded.
 

kwired

Electron manager
Location
NE Nebraska
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).

OP'er said there's a disconnect on the 13.2V primary side of non-POCO transformer (http://forums.mikeholt.com/showthread.php?t=163745&p=1590494#post1590494), but no mention of OCPD... so we're left assuming OCPD is provided on primary (with the xfmr being non-POCO and y'alls comments related to service point ;)).

Anyway, still a feeder, but atypical by definition. It'd be an Interconnected Electric Power
Production Sources feeder, for lack of a better description. This is plainly evident with 705.12(D) revisions of the 2014 NEC edition.

OP'er also did not mention whether secondary is delta or wye configured, or grounded.
Somehow I missed information in that post. To me we need more clarification on service point, it just says the disconnect is the service point. Designating line side of that disconnect as service point makes that disconnect the service disconnecting means (if overcurrent protection is also provided) and load side conductors are feeders. Designating the load side of that disconnect makes the load side conductors service conductors whether there is overcurrent protection or not.
 

JEMENG

Member
Location
NY
Electrical Path as follows:

13.2kV Service Disconnect
13.2kV Fuse
13.2kV/480V transformer (wye grd - wye grd) with primary fusing
480V 1200A disconnect (<25' away, but all equipment outside)

It looks like the overall consensus is the 480V side's non-energized conductors are per 250.66, and that the PV being a source on the 480V side is not the factor in sizing? Just like a typical installation without pv?
 

Smart $

Esteemed Member
Location
Ohio
Electrical Path as follows:

13.2kV Service Disconnect
13.2kV Fuse
13.2kV/480V transformer (wye grd - wye grd) with primary fusing
480V 1200A disconnect (<25' away, but all equipment outside)

It looks like the overall consensus is the 480V side's non-energized conductors are per 250.66, and that the PV being a source on the 480V side is not the factor in sizing? Just like a typical installation without pv?
That's correct... twice over. :D
 

don_resqcapt19

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Staff member
Location
Illinois
Occupation
retired electrician
I believe #5 exists as an original wire size specification of the American Wire Gauge. But I've never seen it commercially available.
I have never seen it as an individual conductor but have installed different sizes of Type G flexible power cable that had 5, 7 and 9 AWG EGCs.
 
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