- 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.We don't see these systems because the NEC has required grounding if 120V is available for several decades.
A standard high leg delta does not have <= 150V on all of its ungrounded conductors, yet it is required to be grounded.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.
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.A standard high leg delta does not have <= 150V on all of its ungrounded conductors, yet it is required to be grounded.
Just because you can, doesn't mean you should. I could make stop-action slow-motion videos of bonsai trees, but I don't.... 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.
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.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...
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.Oh and there are some third world countries with 127v power, derived from 220Y/127