3-Phase Open Delta with Residence Attached

[MJRobinson]

Hello,

I'm trying to figure out a what service is at this location. I thought this was 3-phase 480v until I saw the typical 3-phase delta transformers.

There are two transformers feeding 4 lines to the house meter, along the line, two wires are dropped to the house three carry on to another 3-phase meter.

What confused me was when i was left with only 3-wire without the neutral leading to the pump meter.

See attached.

The Color Coding has red, brown and orange.

Thoughts on what this combo is?

What voltages should be reading A to B?, A to C? and B to C? to figure this out.

Thanks in advance, this forum is awesome.

 

[Smart $]

What you have is likely a 240/120V 3Ø 4W (open delta) service drop. Only A, C, and N are dropped at first meter. A, B, C at pump meter... but N (the grounded conductor) is required by Code to be run to all service disconnecting means.

240V phase to phase
120V A and C to N/G

 

[kwired]

Hello,

I'm trying to figure out a what service is at this location. I thought this was 3-phase 480v until I saw the typical 3-phase delta transformers.

There are two transformers feeding 4 lines to the house meter, along the line, two wires are dropped to the house three carry on to another 3-phase meter.

What confused me was when i was left with only 3-wire without the neutral leading to the pump meter.

See attached.

The Color Coding has red, brown and orange.

Thoughts on what this combo is?

What voltages should be reading A to B?, A to C? and B to C? to figure this out.

Thanks in advance, this forum is awesome.

Is there a grounding electrode conductor running down the pole and a jumper to it from the meter or disconnect? Not exactly NEC compliant way to get the grounded conductor there, but if it is POCO installed NEC doesn't apply either, and I have seen this many times on some older (more like really old) rural services.

 

[JFletcher]

Welcome to the forum.

Hello,

I'm trying to figure out a what service is at this location. I thought this was 3-phase 480v until I saw the typical 3-phase delta transformers.

There are two transformers feeding 4 lines to the house meter, along the line, two wires are dropped to the house three carry on to another 3-phase meter.

What confused me was when i was left with only 3-wire without the neutral leading to the pump meter.

See attached.

The Color Coding has red, brown and orange.

Thoughts on what this combo is?

What voltages should be reading A to B?, A to C? and B to C? to figure this out.

Thanks in advance, this forum is awesome.

It's a high-leg delta 120/240V 3ph4w system. Red (now orange) usually denotes the high leg and is usually on the B phase tho can be on C phase at service equipment/at the meter. If the high leg is on B phase, your voltages would be as follows:

A - N = 120V
B - N = 208V
C - N = 120V

A to B, B to C, and A to C are all 240V.

Whatever leg is 208V to neutral is the stinger or high leg and should have red/orange phase tape.

Your picture is too small to see any detail/words.

 

[Jraef]

And it's not at all unusual that the neutral is not run out to the pump panel, because nothing there needs it. The pump starter would either use a 240V coil, or have its own control power transformer. (The CPT is generally cheaper than running a full size neutral wire for no other reason).

Given that there is no other transformer to feed the residence, I agree it's likely 240/120 3 phase 4 wire delta high leg, not 480 of any sort. The fact that one can is bigger than the other confirms it. That's the transformer with the split phase inside.

 

[MJRobinson]

Thanks

Thanks

Hello,

I am going to be connecting a sub-panel and a solar inverter that requires a neutral.

Attached is another photo that shows the 4th wire as the Cable itself.

I think the photo taken of the breaker is just missing the neutral off to the side?? Thoughts?

Thanks,

Michael

 

[ggunn]

Hello,

I am going to be connecting a sub-panel and a solar inverter that requires a neutral.

Attached is another photo that shows the 4th wire as the Cable itself.

I think the photo taken of the breaker is just missing the neutral off to the side?? Thoughts?

Thanks,

Michael

The AHJ's I have dealt with prefer that for a residential or small commercial PV interconnection where the service is three phase 240/120V high leg, you interconnect with the A and C phases (120V phase to neutral) and ignore the B (high leg) phase.

 

[Electric-Light]

Hello,

I am going to be connecting a sub-panel and a solar inverter that requires a neutral.

Attached is another photo that shows the 4th wire as the Cable itself.

I think the photo taken of the breaker is just missing the neutral off to the side?? Thoughts?

Thanks,

Michael

The solo wire on the smaller transformer is the high leg at the top. The jumper is the left corner.

the remaining are the neutral and right side. You'll just connect solar to the 120/240, most likely which is the bigger transformer.

The small transformer is pretty dedicated for serving just three phase loads and the presence can be more or less ignored at the 120/240 single phase panel.

 

[MJRobinson]

stuck with 3-phase

stuck with 3-phase

The AHJ's I have dealt with prefer that for a residential or small commercial PV interconnection where the service is three phase 240/120V high leg, you interconnect with the A and C phases (120V phase to neutral) and ignore the B (high leg) phase.

I think that's works for smaller systems, but in PGE land we can't be more than a 5k difference in phases, so we're out on that, the older inverters with a transformer could handle it, but the transformerless single phases don't work. So i'm in the boat of using a small dedicated 3-phase, 4 wire inverter.

Thanks,

Michael

 

[Smart $]

I think that's works for smaller systems, but in PGE land we can't be more than a 5k difference in phases, so we're out on that, the older inverters with a transformer could handle it, but the transformerless single phases don't work. So i'm in the boat of using a small dedicated 3-phase, 4 wire inverter.

Thanks,

Michael

Is that POCO "word" or is there possibly wiggle room?

The reason I ask is that under Code this configuration can be considered two services having different characteristics. If POCO does also, then connecting to the residential single phase drop should not invoke the (max?) 5k difference between phases stipulation. They likely have an over-5k difference in phase potential just in the two different size transformers.