404.8 (b)

[texie]

An older rule makes it less likely to be relevant today IMO.

I didn't say I had an opinion on this. I was just citing facts.

 

[Terminator5047]

In that case code would not allow MWBC, and OSHA would be ok with live work.

Neither of those apply code is code. You could mess up with something energized just as easy as de-energized. Sound but hurt I failed an inspection imop

 

[mbrooke]

I didn't say I had an opinion on this. I was just citing facts.

I know, we're cool

 

[mbrooke]

Neither of those apply code is code. You could mess up with something energized just as easy as de-energized. Sound but hurt I failed an inspection imop

Messing up would be in violation of 110.7, among others.

 

[romex jockey]

Any idea on the code's reasoning?

to sell barriers.....~RJ~

 

[electrofelon]

I might actually be in support of this section. Having 480 between two adjacent switches does sound a little scary.

 

[Clayton79]

Doesn’t it have to do with the manufacture voltage rating of the switches themselves perhaps? If you have a 120v switch that’s max rating is 300...? The. To put it in an enclosure exceeding that would violate the installation and pose a fire hazard?...


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[roger]

How is he getting 381 volts vs 397? just curious on how the math works.

But being honest, I can't see a reason for this rule.

Smart$ drew it out few years back.



Roger

 

[steve66]

Any idea on the code's reasoning?

Safety for anyone working on or replacing switches?

But I'm reluctant to circuit any interior lights at 277V anymore. With lower power draws of LED, there isn't that much advantage to using 277V.

And with grounded ceiling grids, working on 277V lights is one of the most likely places for someone to get hurt. Combine that with the qualifications and training for a typical "maintenance person".....

 

[mbrooke]

Smart$ drew it out few years back.

View attachment 2556683

Roger

Awesome!

But I want ask- where does the 30 degree phase shift come from? I'm guessing from a delta-wye transformer? In that case how is the circuit path completed? Would the transfomer's vector group make a difference?

 

[mbrooke]

Safety for anyone working on or replacing switches?

But I'm reluctant to circuit any interior lights at 277V anymore. With lower power draws of LED, there isn't that much advantage to using 277V.

And with grounded ceiling grids, working on 277V lights is one of the most likely places for someone to get hurt. Combine that with the qualifications and training for a typical "maintenance person".....

You saying line to line 208-240 is good?

 

[mbrooke]

Doesn’t it have to do with the manufacture voltage rating of the switches themselves perhaps? If you have a 120v switch that’s max rating is 300...? The. To put it in an enclosure exceeding that would violate the installation and pose a fire hazard?...


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How though? Both yokes are grounded, and there is ample air space between the devices such that dielectric breakdown will not occur steady state or reasonable voltage swells imo.

 

[kwired]

Awesome!

But I want ask- where does the 30 degree phase shift come from? I'm guessing from a delta-wye transformer? In that case how is the circuit path completed? Would the transfomer's vector group make a difference?

In that drawing that Smart$ posted, both "systems" are wye systems and both neutral points are bonded together.

I don't know exactly how to draw it out but guessing if you had a corner ground delta on either side that grounded corner needs to be at same point as the neutral of the wye when you draw it out. That should result in different dimensions from ends of each primary to each secondary line than the wye-wye ended up with. Change the delta to high leg delta and you move things around again.

 

[mbrooke]

In that drawing that Smart$ posted, both "systems" are wye systems and both neutral points are bonded together.

I don't know exactly how to draw it out but guessing if you had a corner ground delta on either side that grounded corner needs to be at same point as the neutral of the wye when you draw it out. That should result in different dimensions from ends of each primary to each secondary line than the wye-wye ended up with. Change the delta to high leg delta and you move things around again.

I'm picturing a wye supply going into a Dyn01 step down.