difference between voltage. (ex: 208/220/240/277)

[George Stolz]

For a full listing of standard USA voltages refer to ANSI/IEEE C84.1.

Geoff, another (perhaps shorter and more accessible) list appears in section 220.5(A) of the NEC.

Edit to add: For even more information on voltages allowed for certain occupancies and appliances, see 210.6. In case you weren't overloaded yet.

 

[kingpb]

The problem I have with NEC 220.5 (A) is that the list of voltages is not all inclusive, particularly it does not list 240/120 V which is the high leg delta system. Also, that there is a difference between 120/208Y and 208Y/120V. Consequently it misleads many people into incorrectly stating it as 120/240V. There is also no mention of voltages above 600 V. Besides, 220.5 (A) is a reference for calculations, it is NOT a reference for properly writing or referring to voltages.

In this case, the NEC is providing the voltages second hand, and it is incomplete. Therefore it is best to always refer to the source of information, in this case ANSI/IEEE C84.1. Unfortunately, many are not familiar with the engineering standards in which the NEC is taken, or that they even exist.

 

[dnem]

The problem I have with NEC 220.5 (A) is that the list of voltages is not all inclusive, particularly it does not list 240/120 V which is the high leg delta system. Also, that there is a difference between 120/208Y and 208Y/120V. Consequently it misleads many people into incorrectly stating it as 120/240V. There is also no mention of voltages above 600 V. Besides, 220.5 (A) is a reference for calculations, it is NOT a reference for properly writing or referring to voltages.

In this case, the NEC is providing the voltages second hand, and it is incomplete. Therefore it is best to always refer to the source of information, in this case ANSI/IEEE C84.1. Unfortunately, many are not familiar with the engineering standards in which the NEC is taken, or that they even exist.

Is there a general rule that can be stated about voltage designation ?
Does single phase always list the voltage to ground first while 3phase lists phase to phase first ?

The problem I have with NEC 220.5 (A) is that the list of voltages is not all inclusive, particularly it does not list 240/120 V which is the high leg delta system. Also, that there is a difference between 120/208Y and 208Y/120V.

120/208Y is 3phase and 208Y/120 is 3phase, both are wye, both have 120volts to ground and 208volts phase to phase.

So what's the difference ?

 

[kingpb]

Please see post #17:

120/208Y is single phase, three wire , open wye service, where 208Y/120v is a three phase, 4 wire service.

I was going to post the whole table, w/ notes but it seems we have lost the capability to upload pictures. Maybe George can get the webmaster to bring it back.

The full table is also reproduced in the IEEE Std 141 Red Book. If you can't get a hold of it, send me a PM and I will see what I can do.

 

[George Stolz]

I was going to post the whole table, w/ notes but it seems we have lost the capability to upload pictures. Maybe George can get the webmaster to bring it back.

Bob (iwire) is the chief moderator, I will send him a PM to ask him to check into it.

 

[dnem]

Please see post #17:

120/208Y is single phase, three wire , open wye service, where 208Y/120v is a three phase, 4 wire service.

I was going to post the whole table, w/ notes but it seems we have lost the capability to upload pictures. Maybe George can get the webmaster to bring it back.

The full table is also reproduced in the IEEE Std 141 Red Book. If you can't get a hold of it, send me a PM and I will see what I can do.

OK, so the rule is 3phase voltages have phase to phase listed first while single phase have phase to ground listed first, correct ?

 

[George Stolz]

Off topic posts moved

Off topic posts moved

I might suggest someone post a new topic under engineering/calculations to discuss the 2 phases of a 120/208Y vs. single phase designation.

Agreed. To continue with the two-phase/single phase discussion, please click here.