250.32(B) curiousity

[kwired]

What code section is that?
And do you know what the reason for it is?

Any winding tap (mid point or not) is not at same potential as the grounded conductor already established back at the source. This makes it an ungrounded conductor and we must provide overcurrent protection on ungrounded conductors.

A center tap on a balanced system is going to be close to same potential as center tap on the source but will vary, but grounding that second neutral point on same system will put current on non current carrying paths between the source and the autotransformer. A grounding transformer basically turns whole system into a grounded system, you would need an ungrounded system to start with.

 

[Open Neutral]

An auto transformer is not an SDS by definition. But it doesn't have to be to be a solution. The problems I see are...
- it's not allowed to reidentify a 6awg from white to green. For a #4 feeder it would be fine.
- it's my understanding that an autotransformer in this situation can only handle a limited phase imbalance. So you may need a bigger transformer than you think you need, depending on the maximum possible load imbalance.

On the color change... OK, I was not aware of that. (Another great idea of mine ruined by Those People...) But it is allowed to recolor 12AWG switch legs, etc. isn't it?

In my scenario the autotransformer would have to handle any 120V loads such as hand tools.It would also handle any 240/120 loads but not 240-only ones. The 120v part of those would be small.

I would think such would not be expensive as it could be any transformer with a sufficient 120-0-120 winding; the other winding would be unused and insulated.

 

[wwhitney]

What code section is that?

210.9 and 215.11 (2014 NEC). I'm not clear on the reason.

Cheers, Wayne

 

[kwired]

On the color change... OK, I was not aware of that. (Another great idea of mine ruined by Those People...) But it is allowed to recolor 12AWG switch legs, etc. isn't it?

In my scenario the autotransformer would have to handle any 120V loads such as hand tools.It would also handle any 240/120 loads but not 240-only ones. The 120v part of those would be small.

I would think such would not be expensive as it could be any transformer with a sufficient 120-0-120 winding; the other winding would be unused and insulated.

You can re-identify a white conductor in a cable assembly if you don't have a grounded conductor in the circuit and wish to use it as an ungrounded conductor regardless of size of conductor. You can not pull a white wire through raceway methods and then re-identify it as an ungrounded conductor.

You can not re-identify a green conductor in any application.