120/208v vs 208y/120v rating callout

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guggemos

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Who knows the correct way to display this common secondary rating of a 3-phase transformer? My rule has always been to show the single phase power first followed by the three phase power.
 
208Y/120 is how I have been told and that is what the NEC does as well.




220.5 Calculations.
(A) Voltages. Unless other voltages are specified, for purposes
of calculating branch-circuit and feeder loads, nominal
system voltages of 120, 120/240, 208Y/120, 240, 347,
480Y/277, 480, 600Y/347, and 600 volts shall be used.
Click to expand...
 
According to the standards:
Three phase is shown with the L-L voltage first.
Single phase is shown with the L-N voltage first.

In real life anything goes, so I try to add Ph and W descriptors:
Three phase
480Y/277 3Ph 4W
208Y/120 3Ph 4W
240/120 3Ph 4w

Single phase
120/208 1Ph 3W
120/240 1Ph 3W
 
Voltage ratings

Voltage ratings

Speaking of the code ... thoughout the NEC it is common to see ratings posted as 120/208-volt or 277/480-volt system (Art. 100, Voltage to Ground).

In 220.5 Calculations, it is spelled out as 208Y/120 and 480Y/277 and it is probably for uniformity and consitency.

It is contractory so it is OK to continue to use 120/208V and 277/480V as Ratings.
 
Well speaking as a Senior Member of the Institute of Electrical and Electronic Engineers (IEEE), I will state that they have published an official ruling on this topic. But I don't know which it is, and I refuse to learn. :roll: If someone wants to look it up and post the official answer (and perhaps Jim has already done that), I will do my best to forget whichever is the official answer as soon thereafter as I can manage. I just don't think it is important to get this "right." :cool:
 
I got in this argument years ago when I worked for Sq. D and had to look it up... with IEEE! Jim's right. L-L first on 3 phase, L-N first on single phase.

Technically then if you are describing a single phase circuit derived from a 208Y/120 3 phase service, as I interpreted that you would call it 120/208 (that was the original topic of the debate I was drawn into). So for example I am being asked to hook up a machine that needs 208V single phase for a motor and 120V single phase inside of it to run controls. The circuit that I run from the 2P breaker in the panelboard would be a 120/208V circuit. But the panelboard itself would be described as a 208Y120 service panel.
 
In Europe for three phase it is usuall to state the the lower voltage first, for example 230/400 volts, but common USA practice is the other way round.
In practice I dont think that it matters much, provided that the meaning is clear.

In the case of single phase, it is usuall only to state the single phase voltage, and not the voltage of the system from which it is derived.
For example the normal household supply would be reffered to as 230 volts here, with no mention of the fact that it is almost certainly derived from a 230/400 volt system. Stating "230/400" would imply a 3 phase circuit or supply, which is the norm in larger premises but not domesticly.

It is normally presumed in the case of a single phase supply that one wire is grounded unless stated otherwise.
In the USA there are numerous instances of 2 wire 208 volt or 240 volt circuits with 2 hot wires. This is almost unknown in Europe.

In the very rare case of say a single phase 220 volt circuit derived from a 4 wire 3 phase, 127/220 volt system, then this should be made clear.
I have only ever worked on one such system in my whole life.
 
Distribution design tech from the poco here. With the transformers at our location, the TRF name plate places the ratings in regards to the windings of the transformer. For instance, if a trf (usually a padmount) has "240/120" it has a secondary coil that is PERMANENTLY in series, and the coils cannot be parralled for 120V at full transformer capacity. the opposite is true for a rating of "120/240" (usually OH TRF). We can pop the lid of the TRF and parrallel the windings to give 120V at full transformer capacity.
 
charlie b said:
Well speaking as a Senior Member of the Institute of Electrical and Electronic Engineers (IEEE), I will state that they have published an official ruling on this topic. But I don't know which it is, and I refuse to learn. :roll: If someone wants to look it up and post the official answer (and perhaps Jim has already done that), I will do my best to forget whichever is the official answer as soon thereafter as I can manage. I just don't think it is important to get this "right." :cool:
Click to expand...

A topic near and dear to me, but at least your consistent with your belief.:roll:

For reference, the standard in question is ANSI C84.1 for system voltages, however the OP related to transformers in which you need to refer to IEEE C57.12.00 Tables 11(a) and 11(b).
 
jim dungar said:
According to the standards:
Three phase is shown with the L-L voltage first.
Single phase is shown with the L-N voltage first.

In real life anything goes, so I try to add Ph and W descriptors:
Three phase
480Y/277 3Ph 4W
208Y/120 3Ph 4W
240/120 3Ph 4w

Single phase
120/208 1Ph 3W
120/240 1Ph 3W
Click to expand...

This what I was taught and what I see on most specs.
 
charlie b said:
Well speaking as a Senior Member of the Institute of Electrical and Electronic Engineers (IEEE), I will state that they have published an official ruling on this topic. But I don't know which it is, and I refuse to learn. :roll: If someone wants to look it up and post the official answer (and perhaps Jim has already done that), I will do my best to forget whichever is the official answer as soon thereafter as I can manage. I just don't think it is important to get this "right." :cool:
Click to expand...

That right there is funny! And I agree. There are bigger things to worry about.
And as Iwire would say: Don't believe everything you see. Test it!
 
According to the standards:
Three phase is shown with the L-L voltage first.
Single phase is shown with the L-N voltage first.

In real life anything goes, so I try to add Ph and W descriptors:
Three phase
480Y/277 3Ph 4W
208Y/120 3Ph 4W
240/120 3Ph 4w

Single phase
120/208 1Ph 3W
120/240 1Ph 3W
Click to expand...

This makes perfectly good sense, therefore it can't be correct. :grin:
 
I was at teh Home Depot and found plastic boxes for dryer receptacle that said ready for 220v, which isn't a standard NEMA voltage.

I take it people use whatever nomenclature they feel like using.
 
120/240V is the nominal system voltage, and 115/230V is the nominal utilization voltage. It is recognized that the voltage at utilization points is normally somewhat lower than at the service point, i.e. 3-5%.

For any specific nominal system voltage, the voltages actually existing at various points at various times on any power system, or on any group of systems, or in the industry as a whole, usually will be distributed within the maximum and minimum voltages. The minimum voltage range for service voltage on a 120/240V system is listed as 114/228V, and for this, the minimum utilization voltage range is listed as 110/220V. The difference being about 3.5%.

These standards are intended to coordinate the voltages so that throughout the range of of actual utilization voltages encountered, the equipment will perform in a satisfactory manner. The nomenclature is very intentional for products that follow industry standards , as are the way voltages are listed in the standards. Whether people accept the use is another matter.

Hope that helps.
 
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I post this a lot but I think it is a great little graphic.

ANSIC841.jpg
 
208Y/120 correctly conveys the derivation of voltage, which is L-L 208, N-L 120 wye three phase source.

120/208v can mean neutral, leg 1 and high leg of 240v center tapped delta, which provides 240v L-L, 120v L-N, 208v HL-N
 
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