ok- single phase wiring- lets do this

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slc410

Electrician
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Madison wi
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Electrician
first off I would like to ask about 3-phase 4 wire 120/240 (b-phase high leg) wiring. I was told that connecting a line to neutral load to the B phase is not permitted but im assuming that what they're thinking is one will connect a 120v load to this connection which obviously will end not so well. But lets say you connect a load which is rated for the 208 volts which this phase provides isnt this an ideal setup for this situation. I think I remember in tech school that this is why this voltage was created in the first place, to provide multiple voltages without having to have transformers all over the place.

Next, somewhat unrelated, but can you wire a lighting ballast rated for only 277 volts (line to neutral) to 208 volts (line to line)? In my 6 years in the trade I had never heard of this till the other day when a seasoned veteran in the trade said it was ok since both voltages are "single phase".
 
slc410 said:
Next, somewhat unrelated, but can you wire a lighting ballast rated for only 277 volts (line to neutral) to 208 volts (line to line)? In my 6 years in the trade I had never heard of this till the other day when a seasoned veteran in the trade said it was ok since both voltages are "single phase".
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No you cannot


277 volts to ground,,,,277 volts line to line is 480 volts

208 Volts Line to Line ,,,,,,A 277 volt ballast requires a grounded conductor so it will blow if you hook it up to 208volts line to line.
 
You can connect loads to the high leg as there is nothing "wrong" with that voltage. The problem is finding the breaker 208 voltage-rated for the high-leg instead of the standard 120/208 rating.

Since it is such an unusual thing to do, I would not recommend connecting single-phase loads to the high leg. It won't blow up if you do but you have to watch your winding loading.
 
mivey said:
You can connect loads to the high leg as there is nothing "wrong" with that voltage. The problem is finding the breaker 208 voltage-rated for the high-leg instead of the standard 120/208 rating.

Since it is such an unusual thing to do, I would not recommend connecting single-phase loads to the high leg. It won't blow up if you do but you have to watch your winding loading.
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Mivey meant a 120/240 rating I think.
 
slc410 said:
first off I would like to ask about 3-phase 4 wire 120/240 (b-phase high leg) wiring. I was told that connecting a line to neutral load to the B phase is not permitted but im assuming that what they're thinking is one will connect a 120v load to this connection which obviously will end not so well. But lets say you connect a load which is rated for the 208 volts which this phase provides isnt this an ideal setup for this situation. I think I remember in tech school that this is why this voltage was created in the first place, to provide multiple voltages without having to have transformers all over the place.
Click to expand...

The high leg is more of a by product of this delta set-up. Generally not used.

Next, somewhat unrelated, but can you wire a lighting ballast rated for only 277 volts (line to neutral) to 208 volts (line to line)? In my 6 years in the trade I had never heard of this till the other day when a seasoned veteran in the trade said it was ok since both voltages are "single phase".
Click to expand...

They make 120V to 277V ballasts that can be hooked up to 208V L-L or L-N, but ya gotta have the right breaker.
 
According to IEEE and ANSI standards the proper way to describe this voltage is 240/120V.
 
slc410 said:
I think I remember in tech school that this is why this voltage was created in the first place, to provide multiple voltages without having to have transformers all over the place.
Click to expand...

As Jumper mentioned it is a by product of the delta system. There is no way to make all three phases 120 volts to any one point on this system. If that is what is wanted you need a wye connected system- but will have to give up 240 volts phase to phase and settle for 208.

Delta connected systems are convenient when majority of load is 240 volt power loads. If the majority of the load is 120 volts the wye system would be preferred. The delta system is also convenient for POCO for remote locations or limited load but three phase is still needed. They can save on equipment cost by installing an open delta system to supply these services.
 
kwired said:
As Jumper mentioned it is a by product of the delta system. There is no way to make all three phases 120 volts to any one point on this system. If that is what is wanted you need a wye connected system- but will have to give up 240 volts phase to phase and settle for 208.

Delta connected systems are convenient when majority of load is 240 volt power loads. If the majority of the load is 120 volts the wye system would be preferred. The delta system is also convenient for POCO for remote locations or limited load but three phase is still needed. They can save on equipment cost by installing an open delta system to supply these services.
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Now many POCO's (including ours) no longer offer 240/120 4W delta services. Hard to find underground transformers wired that way and overhead is going away pretty rapidly. We currently require all new commercial to be underground, and if a customer needs 240 3 phase, they have to use their own step-up transformer.

Maybe for agricultural, there's still a need, but most of the stuff I see is dual rated to 208 or 240.
 
Quote Originally Posted by slc410 View Post
well I could use the vernacular 110/220 which seems to be the way for everyone that doesn't belong to the trade likes to say it!

I think that the 110/220 goes back to one's age. In the "old days", that was what we had, if we had good voltage!
 
LEO2854 said:
No you cannot


277 volts to ground,,,,277 volts line to line is 480 volts

208 Volts Line to Line ,,,,,,A 277 volt ballast requires a grounded conductor so it will blow if you hook it up to 208volts line to line.
Click to expand...
The 208 in this thread is line to ground. It is the high leg of a 4 wire delta system.
There may be safety issues if you supply the fixture with line to line in place of line to neutral, but it will not "blow".
 
meternerd said:
Now many POCO's (including ours) no longer offer 240/120 4W delta services. Hard to find underground transformers wired that way and overhead is going away pretty rapidly. We currently require all new commercial to be underground, and if a customer needs 240 3 phase, they have to use their own step-up transformer.

Maybe for agricultural, there's still a need, but most of the stuff I see is dual rated to 208 or 240.
Click to expand...

I disagree with fact that 240/120 4W delta is no longer offered universally - maybe some places it is.

Pad mount transformers - may be a little more expensive but not that hard to find.

Pole top transformer banks - easiest three phase transformers there is for a POCO - they have all kinds of 120/240 pots around for single phase services, and same pots are used for this setup. If load is limited you can even use just 2 to build an open delta bank - you can use a smaller pot if just the three phase load is limited - you can just add a pot to an existing single phase to get a third phase of limited load. In rural areas you don't have to run all three primary conductors long distances to supply a single service just two phases and a ground.

Around here if you want 120/208 Y it often will cost you more in contruction fees from POCO than a 120/240 delta, for pole top transformers, padmount - maybe the other way around but in those cases you are usually looking at larger capacity - like large enough they would rather use padmount instead of pole mounted transformers.
 
kwired said:
I disagree with fact that 240/120 4W delta is no longer offered universally - maybe some places it is.

Pad mount transformers - may be a little more expensive but not that hard to find.

Pole top transformer banks - easiest three phase transformers there is for a POCO - they have all kinds of 120/240 pots around for single phase services, and same pots are used for this setup. If load is limited you can even use just 2 to build an open delta bank - you can use a smaller pot if just the three phase load is limited - you can just add a pot to an existing single phase to get a third phase of limited load. In rural areas you don't have to run all three primary conductors long distances to supply a single service just two phases and a ground.

Around here if you want 120/208 Y it often will cost you more in contruction fees from POCO than a 120/240 delta, for pole top transformers, padmount - maybe the other way around but in those cases you are usually looking at larger capacity - like large enough they would rather use padmount instead of pole mounted transformers.
Click to expand...

We will not build a open delta bank with padmounts, But offer them overhead to anyone wanting to serve a small three phase load. I have built them with two single phase padmounts in the past. Too many problems with lightning and backfeeding the way padmounts are built...
 
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