208/120 VAC vs. 120/208 VAC

[encoreman]

I just got one of my drawings redlined because I had 120/208 VAC describing a surge suppressor. When I asked why, they said the manufacturer's data sheet called for 208/120 VAC.

I wasn't in the mood to argue, so I just changed it but it started me questioning which is the correct notation.

Any thoughts out there?

Jack

 

[infinity]

Is it 3? or 1??

 

[jim dungar]

Technically 120/208V describes a single phase 3-wire system of 2 hots and a neutral, while 208Y/120 describes a 4-wire system.

This is per ANSI/IEEE standards where single phase systems are listed as LV/HV and three phase systems are HV/LV.
See Informational Note after NEC definition of Voltage, Nominal.

 

[templdl]

Technically 120/208V describes a single phase 3-wire system of 2 hots and a neutral

I believe that you and I would agree that 120/208 would suggest a 1ph3w system but I question if has a "neutral" as the secondary winding of the transformer ii consisted of a 208v single winding would be taped at 120v and 88v or would have 2 windings of 120 and 88v which would not suggest that there would be a center tap.
This is not intended to be nitpicking.
Dave

 

[jim dungar]

I believe that you and I would agree that 120/208 would suggest a 1ph3w system but I question if has a "neutral" as the secondary winding of the transformer ii consisted of a 208v single winding would be taped at 120v and 88v or would have 2 windings of 120 and 88v which would not suggest that there would be a center tap.
This is not intended to be nitpicking.
Dave

Please see the NEC definition of a neutral, and a neutral point.
A neutral conductor carries the unbalance current of the line conductors, it originates at the physical center of a winding set.
1PH 3W does not always mean a center tapped system, even though that is its predominant usage.

 

[templdl]

Please see the NEC definition of a neutral, and a neutral point.
A neutral conductor carries the unbalance current of the line conductors, it originates at the physical center of a winding set.
1PH 3W does not always mean a center tapped system, even though that is its predominant usage.

I see your point. From my experience with transformers I have never run across a transformer which had to be custom made to be applied as such. I sold many transformers that had malt tap but can't recall using a tap in that manor even though it is in fact feasible.

 

[GoldDigger]

Please see the NEC definition of a neutral, and a neutral point.
A neutral conductor carries the unbalance current of the line conductors, it originates at the physical center of a winding set.
1PH 3W does not always mean a center tapped system, even though that is its predominant usage.

But if the 1PH 3W system does not have a center tap, it also does not have a neutral.
And if the intermediate tap is not in the center (as in 120/208 1PH) there is also no neutral. You can have a common grounded conductor for both voltages, but it would not be a neutral.

Informational Note: At the neutral point of the system, the vectorial sum of the nominal voltages from all other phases within the system that utilize the neutral, with respect to the neutral point, is zero potential.

Note that the reference is to all the phases within the system, not within a particular circuit. So by that definition you could have a single line or two line circuit derived from a 3PH wye, and a wire in that feeder or branch circuit which is attached to the center of the wye would still be a neutral conductor.

 

[jim dungar]

But if the 1PH 3W system does not have a center tap, it also does not have a neutral.

That is correct. About the most common one I can think of is a 3W 120/24V control power transformer output. It would be possible to create a 240/480V 3 wire system where the center tap is not the grounded conductor and still be code compliant.

When discussing NEC applications we should use the definitions that actually exist in the NEC.
When we are discussing texts and papers, we should be aware of the different meanings and representations that are possible.

 

[GoldDigger]

When discussing NEC applications we should use the definitions that actually exist in the NEC.
When we are discussing texts and papers, we should be aware of the different meanings and representations that are possible.

:thumbsup::thumbsup:
And the wisdom to know the difference....:roll:

 

[encoreman]

Thanks for your help!

Thanks for your help!

I appreicate the input from everyone. Here is what I distilled from it:
When I am identifying a three phase device such as a generator connected to the system, I will label it:

208Y/120 VAC

When I put a two pole breaker in a three phase panel and connect it to a "single phase" panel I will label the single phase panel:

120/208 VAC

Jack

 

[jim dungar]

I appreicate the input from everyone. Here is what I distilled from it:
When I am identifying a three phase device such as a generator connected to the system, I will label it:

208Y/120 VAC

When I put a two pole breaker in a three phase panel and connect it to a "single phase" panel I will label the single phase panel:

120/208 VAC

Jack

:happyyes:

 

[GoldDigger]

I appreicate the input from everyone. Here is what I distilled from it:
When I am identifying a three phase device such as a generator connected to the system, I will label it:

208Y/120 VAC

When I put a two pole breaker in a three phase panel and connect it to a "single phase" panel I will label the single phase panel:

120/208 VAC

I disagree to the extent that if you have pulled a neutral to the "single phase" panel, it is still a three phase panel, but with only two phases present. As such it would still properly be 208/120, indicating that the 208 is phase to phase and the 120 is phase to neutral but there are still two distinct phases present instead of one split phase. The split phase is the only configuration I would label with LV/HV.
YMMV

Also, if you connect the two phases to a split phase panel you are very likely to confuse anybody who works with it later.

 

[Smart $]

208Y/120 VAC

FWIW, the "Y" is not necessary or required, but also not prohibited.

I disagree to the extent that if you have pulled a neutral to the "single phase" panel, it is still a three phase panel, but with only two phases present. As such it would still properly be 208/120, indicating that the 208 is phase to phase and the 120 is phase to neutral but there are still two distinct phases present instead of one split phase. The split phase is the only configuration I would label with LV/HV.
YMMV

Also, if you connect the two phases to a split phase panel you are very likely to confuse anybody who works with it later.

By the same token, labeling it 208/120V is likely to confuse someone later. IMO, it is better to label as Jim mentioned, but include both phase and wire information...

208/120V 3? 4W

and

120/208V 1? 3W

If any person working in these panels does not know they difference, they are definitely not qualified to do so.

 

[templdl]

FWIW, the "Y" is not necessary or required, but also not prohibited.


By the same token, labeling it 208/120V is likely to confuse someone later. IMO, it is better to label as Jim mentioned, but include both phase and wire information...

208/120V 3? 4W

and

120/208V 1? 3W

If any person working in these panels does not know they difference, they are definitely not qualified to do so.

Is this a real life application or simply a "what if" scenario?

 

[GoldDigger]

FWIW, the "Y" is not necessary or required, but also not prohibited.


By the same token, labeling it 208/120V is likely to confuse someone later. IMO, it is better to label as Jim mentioned, but include both phase and wire information...

208/120V 3? 4W

and

120/208V 1? 3W

If any person working in these panels does not know they difference, they are definitely not qualified to do so.

FWIW, the NEC seems to agree with you, at least in part. The system voltage descriptions in the code always include the letter Y to make them completely unambiguous.

For two-out-of-three line panels, they do just what you recommend:

Example D5(a) Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
All conditions and calculations are the same as for the multifamily dwelling [Example D4(a)] served at 120/240 V, single phase except as follows:
Service to each dwelling unit would be two phase legs and neutral.

And at the individual units:

For 120/208-V, 3-wire system....

But notice that they explicitly label this as V rather than Y. (Which I had not noticed before.)

And, of no small value, this lets them describe the voltage range for appliances as 120/208-240!

 

[Smart $]

Is this a real life application or simply a "what if" scenario?

It appears your question is directed to the OP'er, but quoted my post... :?

 

[jim dungar]

FWIW, the "Y" is not necessary or required, but also not prohibited.

The addition of the Y seems to be preferred by the ANSI/IEEE standards as well as the NEC.

Utilities and textbooks seem to not include it.

Either way LV/HV = single phase and HV/LV = three phase.
Terms like split-phase are not universally understood nor are they unambiguous; for example 2 hots + 1 Neutral is available from other transformer connections besides a center tapped single winding transformer.

 

[templdl]

It appears your question is directed to the OP'er, but quoted my post... :?

Either way would this actually be practical application or is getting to be theoretical?
I'm just intrigued by where this will end up based upon the OP.

 

[Smart $]

Either way would this actually be practical application or is getting to be theoretical?
I'm just intrigued by where this will end up based upon the OP.

Well it definitely appears the OP is a real life application.

I'm perfectly fine with 208/120V for 3? and 120/208V for 1?... but as we all know, the convention is not applied universally.

 

[GoldDigger]

Either way LV/HV = single phase and HV/LV = three phase.

So where, in your opinion which I value, does that leave the "two-out-of-three" phase feeder and panel?

LV
--- ?
HV


LV\HV? LV|HV ?