- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
So laws requiring "dogs" to be on leashes in parks are satisfied if only one dog is on leash? (Depending in the actual wording of course.)
480v to 240v 3ph tranformer x4 tap
- Thread starter Scali
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The actual wording is the key. What if the law says dogs over 10lbs in parks must be leashed?So laws requiring "dogs" to be on leashes in parks are satisfied if only one dog is on leash? (Depending in the actual wording of course.)
In the case of 250.20(B)(1), we can ground the system such that two ungrounded conductors do not exceed 150 volts to ground. It would be much more controversial if only one ungrounded conductor would not exceed 150 volts to ground (such as a corner grounded delta 4-wire system).
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
A very interesting thought, and I would pity the sparky who came on such a system unexpectedly and tried to figure it out from the voltages!
I had to go back and reread 250.20(B)(3) to be sure, but I think that although the intent may have been to require that the neutral be the grounded conductor, it does not actually say that, just that the system must be grounded. Nice hypothetical situation!
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Each of the three options is acceptable, IMHO. Just do not try to combine 1 and 2.
Which would I prefer? Probably 2 (as clarified by Smart $).
Which would I prefer? Probably 2 (as clarified by Smart $).
- Location
- New Jersey
- Occupation
- Journeyman Electrician
There are three ungrounded conductors, one exceeds 150 volts why isn't it that simple?
It can be that simple. Depends on the AHJ's interpretation.
Another point is, none of them exceed 150 volts to ground until one terminal (or conductor, by way of fault) is grounded.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Can't be that simple just because it is in the NEC:happyyes:
And we can butcher any wording that may be printed in there anyway.
We could debate via hundreds of posts just what is meant on page 10 where it says 70-10 at the bottom of the page
As you are required to ground the transformer to building steel it is very easy to ground X4 to the terminal on the case. Most inspectors require this even if you don't have a neutral in your system. This also provides a return path to open the oc protection should you develop a short or ground fault.
- Location
- Illinois
- Occupation
- retired electrician
By definition (NEC Article 100) the voltage to ground for an ungrounded system is the maximum phase to phase voltage.
And that is because a second, different-line-to-ground fault will effect such a differential voltage. However, the system grounding rules are written based on line-to-ground voltage after grounding the system.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Now getting back to the original question here - does the X4 have to be used just because it is there? If it is used then NEC tells us it is the point of the system that is to be grounded.
The real question here is if it is not intended to be used do we have to ground it anyway? Or can we utilize this transformer as a corner grounded system or even an ungrounded system if for some reason we have such need or desire. In either of those instances you have to leave the X4 float or it will cause problems with the scheme of things.
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