Voltage Ratings: 110/115/120, 220/230/240 or 440/460/480

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
Unless it was a “6 wire” system where all of the center points were ungrounded....
We don't see these systems because the NEC has required grounding if 120V is available for several decades.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
We don't see these systems because the NEC has required grounding if 120V is available for several decades.
But 250.20(B) would allow such a system to be ungrounded. The only grounding requirements it has are for systems where there's a conductor <= 150V to all the other conductors, or for the two most common 3-phase 4-wire systems.

Cheers, Wayne
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
But 250.20(B) would allow such a system to be ungrounded. The only grounding requirements it has are for systems where there's a conductor <= 150V to all the other conductors, or for the two most common 3-phase 4-wire systems.

Cheers, Wayne
A standard high leg delta does not have <= 150V on all of its ungrounded conductors, yet it is required to be grounded.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
A standard high leg delta does not have <= 150V on all of its ungrounded conductors, yet it is required to be grounded.
Correct, by 250.20(B)(3), which applies only to "3 phase, 4-wire delta" systems. Add a 5th (or 6th) wire, and 250.20(B)(3) no longer requires the system to be grounded.

Cheers, Wayne
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Oh well, this is kind of like this new argument about whether there were people of color in Middle Earth… it doesn’t exist so it really doesn’t matter what anyone thinks.

I for one apologize for having fed into this divergence. As was already said, there is no 240/120 3 phase 4 wire with 3 separate 120V circuits available, nor would/could there be a 6 wire version for numerous reasons, outside of some phantasy realm.
 

drcampbell

Senior Member
Location
The Motor City, Michigan USA
Occupation
Engineer
... you certainly can create a "240/120 4-wire [system] that has three 120-volt-to-ground legs with no stinger," it just won't be a delta. If the primary is 3-phase, just add another phase to a 120/240V 3-wire secondary system, at some angle to the single phase already present. 60/120 degrees would be easy to do with two transformers. Or you could get 4 wires out of the usual 5 wire 240/120V 2-phase system.

Cheers, Wayne
Just because you can, doesn't mean you should. I could make stop-action slow-motion videos of bonsai trees, but I don't.
 

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
I did a lot of remote cellular telephone equipment shelters in Argentina. Some of those shelters has to be located at the local telephone exchanges. I found that they used all 220 volt tools and appliances, their neutral conductors were blue...
Light blue has become the most common neutral conductor in the world. The NEC has had to allow that color for neutrals in flexible cord.

Oh and there are some third world countries with 127v power, derived from 220Y/127
Yeah not just some, all of South America, its an interesting story, that I'd like to know more about, there were competing standards and for a time they were going with US standards and 208Y/ 120 then they notched it up to 220Y/ 127.
 

garbo

Senior Member
Side note: For years a lot of people called 460 & 480 volts 440 due guess it was faster to say. Anyway while working in a large plant back in the early 80's the engineer in charge of ordering & installation of a state of the art ten millon dollar machine told the European company that we had 440 volts. The 480 volts that we had was closer to 495 volts at night causing one of the computers to trip out due to high voltage on a 24 volt power supply. He spent over 3 grand to have a 440 to 480 volt transformer air freighted to location. Only had 3 input & 3 output wires. After wiring in only the primary measured the secondary and it was only 460 volts. Had the nerve to tell me that I do not know how to connect a three phase transformer. Called him a few choice words over the phone. Turns out he ordered the wrong transformer. Finally we had to adjust taps on 13.2 KV transformer that feed the buss duct that it was feed off of
 
Top