Delta Primary/WYE Secondary

[WGriff53]

I have a transformer in the plant I work in. It was installed to feed a general purpose panel. the voltage measures a-b 208, a-c 208, b-c 240 volts.
My supervisor and I got into a heated discussion about the neutral. yes code does permit using tray cable in industrial applications, which almost always does not have a neutral color. So he says use the black, red, blue with bare ground. use the blue for neutral. Whoooaaaa, I said that's cool, except that you still need to identify the blue, when used as neutral, with white tape.
So now we're making every effort to get our plant up to code. I feel like if you're checking something in the field end fed from this panel, the blue needs to be identified if used for other than a current carrying conductor.
Thanks in advance
WGriff53

 

[templdl]

I have a transformer in the plant I work in. It was installed to feed a general purpose panel. the voltage measures a-b 208, a-c 208, b-c 240 volts.
My supervisor and I got into a heated discussion about the neutral. yes code does permit using tray cable in industrial applications, which almost always does not have a neutral color. So he says use the black, red, blue with bare ground. use the blue for neutral. Whoooaaaa, I said that's cool, except that you still need to identify the blue, when used as neutral, with white tape.
So now we're making every effort to get our plant up to code. I feel like if you're checking something in the field end fed from this panel, the blue needs to be identified if used for other than a current carrying conductor.
Thanks in advance
WGriff53

You's back the truck up. Be somewhat causious when talking to your boss onthis as you may be eatting some crow on this one.
You said that you were working with a wye which is A-B 208v, A-C 208v, and B-C 240v. Don't you think that the 240v is a bit strange? Also noticeable omitted was the L1-N, L2-N, and L3-N voltages are.
And you do have a eye secondary?
Red, Black, Blue are line conductors, the blue is in fact represents a line conductor. The transformer has an X1,X2, X3, line conductors and X0 neutral.
The neutral point is grounded.
You post is somewhat vague with regards to where the feed to you panel is originating from and if it is a main or sub feed panel. It also would be helpful if you to advise where/how the transformer is grounded or if the panel that you are addind is being feed by an upstream breaker.
Incidentlty, that 240v still bothers me.

 

[ggunn]

You's back the truck up. Be somewhat causious when talking to your boss onthis as you may be eatting some crow on this one.
You said that you were working with a wye which is A-B 208v, A-C 208v, and B-C 240v. Don't you think that the 240v is a bit strange?

Actually it's the 208 values that seem strange to me. In a three phase system if one phase is abnormal to neutral, then both phase voltages between it and the other two phases are off while the single phase to phase voltage between the two correct voltages is normal. It seems to me that the A phase is low (or B and C are high).

 

[templdl]

Actually it's the 208 values that seem strange to me. In a three phase system if one phase is abnormal to neutral, then both phase voltages between it and the other two phases are off while the single phase to phase voltage between the two correct voltages is normal. It seems to me that the A phase is low (or B and C are high).

It's difficult to address your question when starting in the middle.
1) what is the name plate on the transformer we which supplies the panel?
2) what is the secondary connections is the transformer?
3) please confirm that the secondary of that transformer is in fact a wye.
4) you overlooked my previous question regarding the L-N voltages for each phase. Is there a reason that this hasn't been addressed?
Both 240 as well as 208v are common voltages. As such let's start with what the nameplate on the transformer is. Take a picture of it and attach it to you reply It would include the the rating, primary and secondary voltage rating, primary taps, and the winding diagram. To say that you have 208-208-240 is strange. Again what are the L-N voltages?
You also state the it's not the 240 that you are questions but its the 208v that you find odd.
You also stated the you have a wye secondary. Being the you stated that all three voltages should be 240v that would make it a 240y which is very strange in the it would have 139v to the neutral.
As such let's start with your supply, the transformer.

 

[WGriff53]

Delta/Wye transformer

Delta/Wye transformer

First of all, I will make sure to get all the info that you have questions about. I think you missed the main question. That was
if I am to use black/red/blue tray cable off this transformer, and designate the blue as neutral, to me the blue should be marked to be identified as neutral.
This transformer has a 277/280 volt primary, but that is not the issue here, identifying the neutral is the question. Is there a exemption in the code to exclude identifying the neutral as white, just because I used tray cable on the secondary circuits?

 

[rcwilson]

Is there a exemption in the code to exclude identifying the neutral as white, just because I used tray cable on the secondary circuits?

Not that I am aware of. Your 3/c cable with a bare ground will have to have one of the wires colored white where ever it is exposed.

Is the load the cable is feeding a single phase load at 208V or two 120V loads. (You did not mention having a neutral on the 208-240V side of the transformer which is what we would expect with a wye secondary).

Or is this wire bringing the 480V power to the transformer? If that is the case, no neutral is needed, just three hot phase wires and a bare ground.

 

[GoldDigger]

First of all, I will make sure to get all the info that you have questions about. I think you missed the main question. That was
if I am to use black/red/blue tray cable off this transformer, and designate the blue as neutral, to me the blue should be marked to be identified as neutral.
This transformer has a 277/280 volt primary, but that is not the issue here, identifying the neutral is the question. Is there a exemption in the code to exclude identifying the neutral as white, just because I used tray cable on the secondary circuits?

I think that there is no question that the wire you use for the neutral would have to be re-identified at the ends and at every access point along the run.
The question is whether you are even allowed to re-identify a phase color as the neutral.
And if your hypothetical circuit uses only two phases, and some other circuit uses a different pair of phases, you will have the problem of not identifying the phases consistently or re-identifying a different color as neutral in the other circuits.

BTW, which two phase lines are you planning to use? The 240V pair or one of the 208V pairs (which I still find hard to comprehend....)

The closest thing to what you describe which is a commonly seen configuration is the high-leg delta. But that would have 240 line-to-line on all phases and 120, 120, and 208 between the three phase lines and the "neutral" which is actually the center tap of one 240 volt delta winding.
But even that does not fit the voltage combinations you describe.

It is possible, with a real wye configuration of windings and a custom made or oddly tapped transformer, to have each of the phase to neutral (center point) voltages be anything you want, but you could not then use those phase lines as a delta connection.

If you really have the three line-to-line voltages you describe, then their phase vectors cannot be at a 120 degree rotation as would be the case for a normal wye or delta.