high leg on a different phase

kwired

Electron manager
Location
NE Nebraska
Sorry for the confusion...I will start again from what I remember

Single phase 208 to a rotary converter output of converter 120/240 3 phase no neutral with high leg. If I need a neutral can I get it from the 208v panel feeding the converter?
What is reason you have 208 volts but yet need a phase converter?

Finding a way to get third phase from the (likely three phase) source is a wiser investment of time and money over using the phase converter. JMO.

Otherwise assuming there is a neutral at your source - then yes.
 

Smart $

Esteemed Member
Location
Ohio
Sorry for the confusion...I will start again from what I remember

Single phase 208 to a rotary converter output of converter 120/240 3 phase no neutral with high leg. If I need a neutral can I get it from the 208v panel feeding the converter?
It is electrically impossible to have 120/240 3? without a neutral and also have a high leg...???

Make and model of the converter or perhaps a link to documentation?

But what point is there in discussing this if there is no neutral connection in the tool???
 

Smart $

Esteemed Member
Location
Ohio
...

Single phase 208 to a rotary converter...
What is reason you have 208 volts but yet need a phase converter?

Finding a way to get third phase from the (likely three phase) source is a wiser investment of time and money over using the phase converter. JMO.
...
Building only has single phase, tool is 3 phase
IMO it's odd that a building only has 208/120V 1? 3W, but if that's what it is, then that's what it is.

Has the owner looked into getting 3? service?
 

kwired

Electron manager
Location
NE Nebraska
IMO it's odd that a building only has 208/120V 1? 3W, but if that's what it is, then that's what it is.

Has the owner looked into getting 3? service?
It has to originate from a three phase system or at least two thirds of a wye bank, but I don't think there is much advantage to building such a bank or you would see it more often.

Maybe it is a single phase from another building or structure that has three phase. Still the cost of a phase converter makes it worth considering bringing the third phase to this location.
 

ronaldrc

Senior Member
Location
Tennessee
Sorry for the confusion...I will start again from what I remember

Single phase 208 to a rotary converter output of converter 120/240 3 phase no neutral with high leg. If I need a neutral can I get it from the 208v panel feeding the converter?



I'm confuse, If the output of this phase converter is 120/240 3 phase it has to have a neutral to get the 120 volts from. Doesn't the wiring diagram of this phase converter show a neutral.

If it has a neutral it is either all ready gounded the converter frame, if it is not and floating the instructions should show how to deal with it.

Measure from the high leg and see if you get 208 to the metal frame and from the other two legs and see if you get 120 if so it has a neutral, if so now you need to find that neutral lug or terminal.

Ronald :)
 

GoldDigger

Moderator
Staff member
Going back to the original question about getting shocked:

The only way this could make a difference is if the concern is the line to ground voltage and its effects on the wiring and component insulation. Which in the US would have to be capable of handling it anyway. And as long as the EGC is good, no exposed metal parts should end up energized.

Sure sounds like an incorrect statement. Damage to the machine? Maybe. Shock to user? Not likely.
 

kwired

Electron manager
Location
NE Nebraska
I'm confuse, If the output of this phase converter is 120/240 3 phase it has to have a neutral to get the 120 volts from. Doesn't the wiring diagram of this phase converter show a neutral.

If it has a neutral it is either all ready gounded the converter frame, if it is not and floating the instructions should show how to deal with it.

Measure from the high leg and see if you get 208 to the metal frame and from the other two legs and see if you get 120 if so it has a neutral, if so now you need to find that neutral lug or terminal.

Ronald :)
Output of a rotary phase converter is not a separately derived system. It is the two input conductors plus the developed third phase. That phase will not be 120 volts to ground, it will not be 208 volts to ground. It will vary depending on load conditions, and motor currents will not be equal across all phases. If you need a neutral for a load, you must connect the load from one of the input lines to the neutral of the input source. Most of my experience with these comes from 480 volt units, but is still similar trends.
 

Fulthrotl

~~Please excuse the mess. Sig under construction~~
Are you saying the equipment has to be designed with a high leg in mind?
usually, i'd say not, but i have seen equipment that doesn't use a control transformer,
instead just taking one leg of 240 delta, or 208 wye... no problem if it's a wye...
but if it's a delta service.....

most machine tools and similar stuff use a control transformer,
so that can't happen, and generate their own control power.

i just put in a service that was 240 delta, and the high leg was marked by
both the panel manufacturer, and specified on the drawings, to be "C" phase.

everywhere else i've been, it's been "B" phase....
 

hurk27

Senior Member
I really think the OP needs to get someone who knows a little about rotary phase converters to help him with this?

First are you going to get 240 volts out of a phase converter fed from 208?, second, if a neutral is needed then the neutral load must come from one of the two passed thru phase conductors from the supply as well as a neutral fed from the panel, I have yet to ever seen a neutral derived from the phase converter as if you have a single phase system you will have two of the supply conductors with 120 to the supply neutral.

Another problem I see is can you use a 240 volt rated rotary phase converter on 208? I have never had a situation where I had to do this, if I had 208 I had 3-phase, I can see a very big voltage problem with the derived phase as the two pass through phases will stay at 208, but the derived phase will be what? talk about not having a balanced voltage because the rotary phase converter is going to try to keep the rpms of 60hz so will the voltage on the derived phase be 240?

I could see a 200 volt rated motor used as a rotary phase converter working but not a 240 rated one.

Static converters will just put out what is put in, so if you put 208 in you get 208 out.
 

hurk27

Senior Member
usually, i'd say not, but i have seen equipment that doesn't use a control transformer,
instead just taking one leg of 240 delta, or 208 wye... no problem if it's a wye...
but if it's a delta service.....

most machine tools and similar stuff use a control transformer,
so that can't happen, and generate their own control power.

i just put in a service that was 240 delta, and the high leg was marked by
both the panel manufacturer, and specified on the drawings, to be "C" phase.

everywhere else i've been, it's been "B" phase....
Here existing 4-wire deltas have the high leg landed as C in the meter socket but rotated to B in the panel, by rotated I mean rotation kept the same so meter A will wind up on panel C and meter B will wind up on panel A, 4-wire delta are no longer allowed here by the POCO. The NEC requires the high leg to land on B in the panel it cares less where it lands in the meter.
 
Top