Is this panel 480 Wye or 480 Delta?

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SolarCenTex

Member
Location
Texas
My challenge is determining the correct 480V configuration so I can use a
3-phase Solar Edge 10000 for a 12KW commercial system. The SE10K requires a
480V Wye configuration.

The main 480 panel looks straightforward. L1, L2, L3 come from below grade
to three separate busbars in the panel. A 4th wire, not taped white, goes
to what appears to be a ground bar at the lower right of the panel. Green
and green-taped wires come from this bar. I do not see any physical
connections between the L1, L2, L3 bus bars and the ground bar in the lower
right, other than the box itself as the ground bar appears to be bonded to
the main box itself.



Voltage measurements depicts 480V at line to line, and 277 Volts from each
line to the ground (neutral?).



The overhead service at the road depicts 4 wires into the service head. The
three from the three each transformers at the pole are taped traditional
3-phase colors. The bare wire from the pole to the service head is bare
wire, but is taped white as it goes into the service head with an insulated
conductor (wire). There is no apparent ground wire at the pole or inside
the building that I can see but the service is underground and under
concrete until it comes up inside the facility at the 480 panel board.



My master electrician is researching to determine the type but I wanted to
post it here for comments, too.



My questions:

- Is it possible to have an ungrounded Wye where the "4th wire"
actually is a neutral to the lower right bus bar, and the wires leaving that
bar are in fact ground wires?

- The SE10K calls for a neutral wire in a Wye config. If this 4th
wire is a neutral, and is bonded to ground, can I run a wire from this to
the inverter neutral, then another wire from this same bar t0 other ground
wire location in the SE10K (right beside the neutral).

- Is the white taped wire (the bare wire from the pole, then
insulated and taped white into the service head) a neutral or is that
ground.

- Can anything other than a 480 Wye give the 480/277 voltages
indicated above?

- If the 4th wire is a neutral (I certainly hope it is), where
might I find the ground electrode conductor (the building is relatively new,
less than 10 years I believe.). FYI, the building is metal.



I look forward to your comments
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Most likely the fourth conductor from POCO is a true wye center point neutral and is grounded at the POCO side.
POCO does not supply a ground-only wire like the EGC you use on the customer side.
Instead.
So, the POCO grounded neutral comes into the single combined ground/neutral bar where it is joined by the GEC from the local ground system. From there separate EGCs and neutrals will run to each feeder and branch circuit.
In some cases (pure delta three phase loads) there may not be a neutral, just three phase lines and an EGC.
 

SolarCenTex

Member
Location
Texas
So, the POCO grounded neutral comes into the single combined ground/neutral bar where it is joined by the GEC from the local ground system.

My first inclination (hope) is that this is the case, but I keep getting hung up on fact that I cannot see / determine where a a GEC links into this. Could the neutral and ground be bonded ahead of the 480 distro panel?

Thanks for your review and previous assessment.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
My first inclination (hope) is that this is the case, but I keep getting hung up on fact that I cannot see / determine where a a GEC links into this. Could the neutral and ground be bonded ahead of the 480 distro panel?

Thanks for your review and previous assessment.
Yes, it could, but to comply with current code I would expect the neutral and ground bus to be isolated in this panel if the bond is upstream.
So I am puzzled too, unless one of the bare or green taped wires is really the GEC.
 

SolarCenTex

Member
Location
Texas
A distribution panel...not a main service. May that why no neutral in the distro pane

A distribution panel...not a main service. May that why no neutral in the distro pane

As I review the layout, I'm at point of thinking that neutral to Ground connection is at pole outside where meter is located. A gutter and two disconnects are there and I'm betting that the neutral to ground bond is there.

But still no neutral it appears in this distro panel.

Must I run a neutral 300 feet underground to this panel in order to connect a neutral wire to my inverter

OR

Can I use the EGC and bring one wire from the ground bus bar in the distro panel to the neutral position and one to the ground position?

Either way, I'm supplying a ground reference to the inverter?
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
If the service includes a grounded neutral conductor, I believe that the NEC requires it to be available at the service disconnect. That may be the fourth wire from POCO.
If none of the existing loads use the neutral, the NEC does not require it to be carried beyond that point.
But your inverter requires a neutral for voltage reference, even though the power flow is entirely on the delta connection.
You need to find out exactly what the service is and what bonds are upstream of the panel.
If that wiring is not NEC compliant, it will have to be corrected.
 

SolarCenTex

Member
Location
Texas
You need to find out exactly what the service is and what bonds are upstream of the panel.

Start point for the day - thanks for your insights. I'm convinced the Wye is here but the neutral must be "found" and brought forward to my panel. Easier said than done but the alternative ("Sir, we picked the wrong inverter..").

I'll keep you informed as to the outcome.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Start point for the day - thanks for your insights. I'm convinced the Wye is here but the neutral must be "found" and brought forward to my panel. Easier said than done but the alternative ("Sir, we picked the wrong inverter..").

I'll keep you informed as to the outcome.

Sight unseen, I tend to agree that you have a 480Y/277 system (your voltage readings seem to confirm that) and the neutral stops at the service disconnects.
What type of conduit system connects your service disconnects to the panel in question ?
As an advocate of equipment grounding conductors (wire type) I hate to open the possibility, but if you have a metallic conduit system that could be used as your EGC and you could convert the
existing "wire" to a neutral ].
 

SolarCenTex

Member
Location
Texas
but if you have a metallic conduit system that could be used as your EGC and you could convert the
existing "wire" to a neutral ].

I must have heard your fingers typing! I was just planning my line of attack for the day and am considering this. But, I'm confident this is Sched 40 conduit across the yard.

I wanted to review the current EGC size to see if it met a neutral conductor sizing requirement.

May I ground the box locally (I'm in a huge metal building built on concrete, I'll look for an existing building GEC system) and then possibly do as you're recommending???
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I must have heard your fingers typing! I was just planning my line of attack for the day and am considering this. But, I'm confident this is Sched 40 conduit across the yard.

I wanted to review the current EGC size to see if it met a neutral conductor sizing requirement.

May I ground the box locally (I'm in a huge metal building built on concrete, I'll look for an existing building GEC system) and then possibly do as you're recommending???

I think you would be "grasping at straws" but considering your predicament it might be worth talking to your AHJ IF the initial install was completed before 2008 and conditions are such that the grounded conductor could have been used as the grounding means provided the guidelines in 250.32 were met.
I think the possibility is slim that all the requirements on in place but it's worth a look.
 

under8ed

Senior Member
The advice of a simple call to the power company sure makes perfect sense; but since the transformers & wiring can be seen at the pole, you may be able to determine what they are going to tell you. If you are not sure what to look for, there are some decent pictures & drawings of 3 phase, pole mounted transformers online.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Although confirming the system with POCO would be productive, from the OP's posts it sounds like this is a subpanel (downstream from his service disconnects at the pole). If that is the case, even if the service is Wye, a neutral might not have been brought to this panel.
 

Smart $

Esteemed Member
Location
Ohio
Although confirming the system with POCO would be productive, from the OP's posts it sounds like this is a subpanel (downstream from his service disconnects at the pole). If that is the case, even if the service is Wye, a neutral might not have been brought to this panel.
That's a noteworthy possibility. Currently leaning the other way, though. POCO could at least verify whether the transformer [bank] secondary is wye or not.

Regarding other "highlights", GoldDigger brought up SBJ upstream. SolarCenTex brought up gutter, two disconnects, and meter at pole... but earlier referred to wire going into "service head" taped white and phase taping on other conductors. I'm doubting any competent electrician would white tape a ground. The two disconnects throw in a measure of uncertainty... but I'm thinking they are actually POCO required. It would help to know whether either is a fused disconnect, plus line and load wire sizes, number and any phase taping, etc. If both are "sealed", then they are under exclusive control of POCO and not an NEC service disconnect.

If premises only requires the ungrounded conductors, it is commonplace for the switchgear to not have a neutral bus and SBJ. Engineers just spec' equipment as 3? 3W, and land the grounded service [neutral] conductor on the ground bus. It is only required to bring the neutral to the service disconnect... it is not required for it to be treated any particular way once it gets there other than connected to the GES and EGC systems.
 

meternerd

Senior Member
Location
Athol, ID
Occupation
retired water & electric utility electrician, meter/relay tech
If the service includes a grounded neutral conductor, I believe that the NEC requires it to be available at the service disconnect. That may be the fourth wire from POCO.
If none of the existing loads use the neutral, the NEC does not require it to be carried beyond that point.
But your inverter requires a neutral for voltage reference, even though the power flow is entirely on the delta connection.
You need to find out exactly what the service is and what bonds are upstream of the panel.
If that wiring is not NEC compliant, it will have to be corrected.

If the transformer bank has a grounded common (neutral) point, Code says the neutral must be run to the service disconnect (250.24.C) even if it will not be used for 277, so if you have a bare wire, that's what you've got. You can verify it by looking at the bank wiring. If three of the secondary bushings are jumpered together, it's Wye. The reason I restated it is because some older service drops did not include the neutral conductor even when the bank was a grounded Wye. The bare was just a ground wire. Found a few here I had to fix. They fed a 480 pump station with no 277 loads.

Not sure if was always a requirement or not.
 
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