PV Interconnection at the Secondary of the Existing Transformer

TheElectrician

Senior Member
Hey guys,

We are doing a project where the final interconnection of the PV system is at the secondary of the existing transformer at the site (that also supplies the building). We asked the POCO for their guidelines for this interconnection (either to penetrate the t/f from the side or to go underground, etc) because the transformer is owned by them, but they said "Ask your Electrician". We are in talks with the couple of people, but did anyone here do such interconnection previously? if so how did you go about it?

Ps. This T/F is located just outside the building above ground and installed on a PAD (Check attached)
 

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ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Where is the POCO's revenue meter? Most POCOs will not allow you to connect outside the meter.
 

TheElectrician

Senior Member
Just come up from underground like the existing service conductors. I can't imagine any POCO allowing anything else.
Thank you, is there any NEC code that we have to comply while doing such Interconnection?

Also, since the transformer is already installed won't that be a task to trench into it? Or I am thinking to remove that transformer, then trench it, install conduits, pull the wire and then connect back the transformer. Wonder how much this is going to cost considering we have to provide a backup generator until we do this work! :huh:
 
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Thank you, is there any NEC code that we have to comply while doing such Interconnection?

Also, since the transformer is already installed won't that be a task to trench into it? Or I am thinking to remove that transformer, then trench it, install conduits, pull the wire and then connect back the transformer. Wonder how much this is going to cost considering we have to provide a backup generator until we do this work! :huh:
Get a locate on the existing conduits, core a hole thru the slab, dig under to meet the new hole. Get everything set up and I bet its just a 1-2 hour outage.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
Thank you, is there any NEC code that we have to comply while doing such Interconnection?

Also, since the transformer is already installed won't that be a task to trench into it? Or I am thinking to remove that transformer, then trench it, install conduits, pull the wire and then connect back the transformer. Wonder how much this is going to cost considering we have to provide a backup generator until we do this work! :huh:
You will need to work with the POCO as some, depending on the size and POCO standards, are sitting on a vault or just a concrete pad with a rectangular hole. Normally there is no need to remove the xformer. Not a big deal to do but details are important.
 

TheElectrician

Senior Member
You will need to work with the POCO as some, depending on the size and POCO standards, are sitting on a vault or just a concrete pad with a rectangular hole. Normally there is no need to remove the xformer. Not a big deal to do but details are important.
This T/F is sitting on a concrete pad with a rectangular cut out like in the pictures. We don't want to remove the transformer as well. I guess I will talk with my electrical contractors and do something like what electrofelon suggested.
 

pv_n00b

Senior Member
Location
CA, USA
Thank you, is there any NEC code that we have to comply while doing such Interconnection?
The conductors between the utility-owned transformer and the Point of Common Coupling (PCC) are usually utility-owned. You might have to install them to the utility's specs but then they usually take ownership. The NEC provides some basic guidance for these conductors in NEC 230 Part III. From the PCC to the service disconnect the conductors are Service Entrance Conductors under NEC 230 Part IV.
 

TheElectrician

Senior Member
The conductors between the utility-owned transformer and the Point of Common Coupling (PCC) are usually utility-owned. You might have to install them to the utility's specs but then they usually take ownership. The NEC provides some basic guidance for these conductors in NEC 230 Part III. From the PCC to the service disconnect the conductors are Service Entrance Conductors under NEC 230 Part IV.
Got it, Thank you very much!
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
The point of delivery (common coupling) is the secondary side of the XF.
On our system they will always be your wires, we never take ownership of your equipment.
metering here is easy. Slip on CTs over the spades, done...
the pad is a spec pad probably. Ours have a 4’X18” opening.
electricians dig under ours with no problem. We open the XF door while they are working to get in their conduits. If the XF is in service now you will have to come up with a safe plan to pull your conductors in.
I have rubbered up the spades and connectors for electricians many times for pulls.
I wouldn’t imagine the POCO would just open and leave...
 
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