480/277 WYE service to 120/240 Single phase

Status
Not open for further replies.
You don't need to have a "main shut off box",

Well...are you sure?
The main switch is what makes the meters cold.
So with a 480/277V 3 phase account AND a 277/480 1 phase account, no main switch would really mean TWO main switches- I don't think POCO wants that.
They want a main switch, then a load panel for each customer- that way it's one service xfmr-wise, with two totally separate accounts bill-wise...and that set-up messes up the line-side (hot meter side) PV connection idea.

If the PV has to be load side, it has to be on the 3 phase customer load side- so you need that upside down T to accomplish the "load panel for each customer" idea.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Well...are you sure?
The main switch is what makes the meters cold.
For cold sequencing, each meter needs a disconnect before it, but there doesn't need to be a single disconnect for both meters. Each meter could have its own disconnect before it.

So with a 480/277V 3 phase account AND a 277/480 1 phase account, no main switch would really mean TWO main switches- I don't think POCO wants that.
I haven't read your National Grid book to see if they allow that, but from what I've read here on other threads, that would be a pretty standard arrangement in most parts of the country.

They want a main switch, then a load panel for each customer- that way it's one service xfmr-wise
The arrangements of meters/disconnects has nothing to do with transformers.

Cheers, Wayne
 
For cold sequencing, each meter needs a disconnect before it, but there doesn't need to be a single disconnect for both meters. Each meter could have its own disconnect before it.
The arrangements of meters/disconnects has nothing to do with transformers.

I can't see how two main service disconnects would work visually.
Right now the service is this, there is no PV-
Two POCO wires coming from the 4 POCO wires running along the road- that's a line and a neutral, so they run 200+ feet from the road overhead to a pole (across one support pole) to a 7200 L-N to 120/240 xfmr, 25kVA.
The 3 wires for the 120/240 run from the pole to a building, overhead, through the meter (it's hot) to the main switch. The main switch is 400A and there are 3 or more load panels from that going to various buildings (one is the residence that isn't supposed to use PV according to the weird rule.)

With the PV (480/277 wye Sunny Tripowers), the service will be changed to 480/277 wye, hopefully 100A and not the standard 200A, because 90kVA of xfmrs for 83kVA of "service" is plenty for 72A max PV output and less than 25kVA max load. (I think)

So that service would be all 4 wires from the road, to the same pole where the 25kVA xfmr is now, running down to the ground with say 3 30kVA xfmrs on a pad, 12.47kV delta on the grid side and 480/277 wye on the service side- from there (the base of the pole), the 4 wires would go underground to the same building (actually a 6x8 foot shed outside the building) where currently the meter is on the outside and the main switch is inside.

The meter can stay where it is, the new meter will go right near it (but not in the same socket or enclosure).
The 480/277 wires will go to the switch first, and then those meters will be cold, but they can't be on the same line because they'd be double measuring something.
So you have to split it there- technically, both meters would still be "hot" after you threw the main switch until you threw the PV disconnect switch.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
I can't see how two main service disconnects would work visually.
I described one possibility earlier: "In practice, I think you'd typically bring your service entrance conductors into a gutter/tap box, make your connections there, and then come out of the gutter separately to the three phase disconnect/meter and to the single phase disconnect/meter."

So that service would be all 4 wires from the road,
I think the POCO transformers typically are delta on the grid side, so they'd only need to bring 3 wires from the road to their transfromer. [Edit: or do they need to bring the HV neutral for bonding?]

So you have to split it there- technically, both meters would still be "hot" after you threw the main switch until you threw the PV disconnect switch.
If the inverters are grid tie inverters, then throwing the main disconnect should cause them to stop producing power for anti-islanding.

Cheers, Wayne
 
1. I described one possibility earlier: "In practice, I think you'd typically bring your service entrance conductors into a gutter/tap box, make your connections there, and then come out of the gutter separately to the three phase disconnect/meter and to the single phase disconnect/meter."

2. I think the POCO transformers typically are delta on the grid side, so they'd only need to bring 3 wires from the road to their transfromer. [Edit: or do they need to bring the HV neutral for bonding?]

3. If the inverters are grid tie inverters, then throwing the main disconnect should cause them to stop producing power for anti-islanding.

1. Well, golly, I just found this in italics below. So you *can* have either/or. Hmm. I'm assuming OR dual secondary xfmrs means in that case there's a single primary.

2. I think you are right there- I tried looking it up just now- seems to be the case as far as I can see.

3. Also a good point, thamks.

4. I just sent the POCO guy an email, so hopefully I'll have some answers Monday.

12. Multiple service facilities may be supplied to the customer from the Company’s Distribution
EPS. These service installations may be either dual primary switchgear or dual secondary
transformers. To assure that the reliability and proper protection are maintained in these
multiple service facilities, the Customer-Generator is not permitted to:
• Parallel secondary services from a common facility.
• Parallel secondary facilities supplied from separate locations.
• Exceed the ampacity rating of any service facility.
• Create an unbalanced loading condition in excess of 2% voltage unbalance between
phases of a service
 
Status
Not open for further replies.
Top