NEC 300.3 (B) Ramifications, Engineering Question

[ken2lsi]

I recently ran accross a single family dwelling installation where the electrician had a 6/2 WG ran to a 240V sub panel for a spa. After the arrival of the spa it was determined a neutral was required. So the electrician added a #10 THWN from the service panel, through the attic, to the sub panel. Clearly this is more than 1 specific violation and not the basis for this question.

The question is, with the neutral conductor being seperate from the phase conductors, and of different characteristics, what would be the specific reasons for premature failure of the electronic circuit board in the spa? I suspect the board mounted transformer is a 120V primary but have not confirmed this.

I have seen before on a 3 phase lighting circuit where only two of the phase conductors were brought down each row, caused the ballasts to prematurly fail. When the installation was changed to include all of the branch circuit conductors in the same raceway, the ballasts functioned normally.

 

[iwire]

I have seen before on a 3 phase lighting circuit where only two of the phase conductors were brought down each row, caused the ballasts to prematurly fail. When the installation was changed to include all of the branch circuit conductors in the same raceway, the ballasts functioned normally.

This makes no sense, there must have been more to it.

 

[al hildenbrand]

Considering the special case laid out in 300.3(B)(3), I ask, what is the wiring method(s) of the energized conductors and the grounded conductor? If they are nonferrous, then 300.3(B)(3) would seem to apply.

Say the 6/2 WG is NM and the #10 is in PVC, then all's right with the NEC.

Integrated circuit failure . . . well, I'm with Bob.

 

[ken2lsi]

This makes no sense, there must have been more to it.

The circuit was a 3 phase 480V 30A lighting circuit connected to low bay fixtures with 480V ballasts. The conduit grid had a North/South conduit run with all 3 phase conductors, originating at the panel. Each East/West conduit run had only the 2 phase conductors pertaining to that row, AB row 1. AC row 2, BC row 3, etc. The installation was corrected by adding the missing phase in each conduit and connecting the fixtures to alternate between the phases down each row as opposed to the entire row being on only 2 phases.

 

[roger]

The circuit was a 3 phase 480V 30A lighting circuit connected to low bay fixtures with 480V ballasts. The conduit grid had a North/South conduit run with all 3 phase conductors, originating at the panel. Each East/West conduit run had only the 2 phase conductors pertaining to that row, AB row 1. AC row 2, BC row 3, etc. The installation was corrected by adding the missing phase in each conduit and connecting the fixtures to alternate between the phases down each row as opposed to the entire row being on only 2 phases.

There is nothing wrong with the installation just using two phases and that would have nothing to do with the ballast failures. As Iwire said, there has to be other factors.

Roger

 

[highvolts582]

harmonics and fire?

harmonics and fire?

I always thought if you ran the neutral without it being near the phase conductors it could vibrate in a pipe/ could burn or catch fire and cause high harmonic distortion in the area. i dont know.