208 volts single pole usage ?

[mbrooke]

I would hate to put a new electric range on that. There’s always the possibility of getting the clock or other 120 V stuff on the range hooked to the wrong leg

Are you kidding me? Delivery guys come, plug new range in- then it smokes. "Something wrong with your electrical sir" Don't think warranty covers such. The control board and clock cost as much as a new range.

 

[jim dungar]

Seems to me that 120/240V 3 phase 4 wire "high leg" systems consistently generate more questions than anything else on this forum...

I agree.

I believe instructors don't spend time on it because they were taught it is 'uncommon' in their area. Uncommon does not mean rare or unheard of, it simply means you will run into it somewhere in your career, just not once a month.

 

[mbrooke]

I agree.

I believe instructors don't spend time on it because they were taught it is 'uncommon' in their area. Uncommon does not mean rare or unheard of, it simply means you will run into it somewhere in your career, just not once a month.

In some areas of the country or a particular area, POCO, country, ect high leg is almost every other 3 phase service. Some POCOs have disallowed high leg for new service since the 70s, others still offer it to this day.

 

[LarryFine]

I find that it helps to remember that the high-leg open delta actually started as a modification to existing single-phase services.

A high-leg delta supply is a 120/240v 1ph supply superimposed on a regular delta 3ph supply it has the characteristics of both.

 

[Jraef]

I find that it helps to remember that the high-leg open delta actually started as a modification to existing single-phase services.

A high-leg delta supply is a 120/240v 1ph supply superimposed on a regular delta 3ph supply it has the characteristics of both.

Yes, but it still leaves a lot of people confused as to the nature of the "208V circuit" and whether or not it can be used. I find it simplest to just tell people NO, it can't be used as a single phase 208V circuit. The rare oddball opportunities to use it are not worth the added confusion it fosters to keep discussing it as if it were (useful). Just fugedaboudit.

 

[LarryFine]

Mathematically, it works; electromagnetically, it doesn't.

"In theory, there is little difference between theory and practice; in practice, there is great difference."

 

[mbrooke]

electromagnetically?

 

[LarryFine]

electromagnetically?

Isn't that how transformers work?

Device ratings aren't the only reasons to avoid doing it.

 

[mbrooke]

Isn't that how transformers work?

Device ratings aren't the only reasons to avoid doing it.

Yes- but what does it have to do with a high leg?

 

[LarryFine]

Yes- but what does it have to do with a high leg?

It's my understanding that the center-tapped secondary doesn't fare well being loaded like that.

 

[mbrooke]

It's my understanding that the center-tapped secondary doesn't fare well being loaded like that.

Depends- I think.

 

[GoldDigger]

Depends- I think.

As mentioned elsewhere a lot depends on whether the 4-wire high leg circuit is supplied by a single core three phase transformer or by two or three individual pots, where the 120-0-240 is a significantly larger pot. Even then the high leg to neutral single phase circuit path is not intended to be used.

 

[mbrooke]

As mentioned elsewhere a lot depends on whether the 4-wire high leg circuit is supplied by a single core three phase transformer or by two or three individual pots, where the 120-0-240 is a significantly larger pot. Even then the high leg to neutral single phase circuit path is not intended to be used.

I'm thinking we need some math in this thread?

 

[GoldDigger]

I'm thinking we need some math in this thread?

What is this "math" you talk about?

 

[mbrooke]

What is this "math" you talk about?

That all high legs can be loaded to some degree or another in theory. I mean will 10 amps really trip a main or burn out a pot? What about 30? 50?

 

[GoldDigger]

That all high legs can be loaded to some degree or another in theory. I mean will 10 amps really trip a main or burn out a pot? What about 30? 50?

I don't think anyone is asserting that using the high leg to neutral circuit will trip a breaker (although a slash rated breaker is simply not allowed.) The effect on the pots, on the other hand is something whose math is most accessible to the transformer manufacturer, which is where the common 5% figure comes from. And as far as I have seen is only stated in relation to unit three phase transformers.

 

[mbrooke]

I don't think anyone is asserting that using the high leg to neutral circuit will trip a breaker. The effect on the pots, on the other hand is something whose math is most accessible to the transformer manufacturer, which is where the common 5% figure comes from. And as far as I have seen is only stated in relation to unit three phase transformers.

But surely anyone could hand calc a 2 or 3 bank setup like a 75/25kva setup or a 167/167/167 type deal.

 

[mbrooke]

I don't think anyone is asserting that using the high leg to neutral circuit will trip a breaker (although a slash rated breaker is simply not allowed.) The effect on the pots, on the other hand is something whose math is most accessible to the transformer manufacturer, which is where the common 5% figure comes from. And as far as I have seen is only stated in relation to unit three phase transformers.

Apparently high legs are also seen on generators

 

[GoldDigger]

Apparently high legs are also seen on generators

What's a generator but a rotating transformer....

 

[kwired]

Seems to me that 120/240V 3 phase 4 wire "high leg" systems consistently generate more questions than anything else on this forum...

Corner grounded delta's seem to raise a lot of questions also.