high leg on a different phase

uwireme

Member
Location
Cottonwood, CA
I hooked up a straight 3 phase no neutral wood working tool, called the manufacture to find out where to land the high leg and was told in the middle. Checked rotation no wire changing needed? all was good.

Got a call from the customer that some parts of the tool stopped working, manufacture came over and found high leg was not on the correct phase and told my customer he could have been shocked.

I have not talked to the manufacture yet but do some pieces of equipment require the high leg on a specific phase? And how could my customer be shocked by installing the high leg on a different phase?
 

Smart $

Esteemed Member
Location
Ohio
...

I have not talked to the manufacture yet but do some pieces of equipment require the high leg on a specific phase?
If the equipment was designed for a high leg supply, it should be "B" or its equivalent. Beyond that, I would imagine there are some non-standard equipment out there.


And how could my customer be shocked by installing the high leg on a different phase?
The only way I can think of would be subjecting parts to a voltage higher than rated for and causing a fault. But IMO that says the product is of a marginal design.
 

Smart $

Esteemed Member
Location
Ohio
Are you saying the equipment has to be designed with a high leg in mind?
Well that's a loaded question for sure, with the multitude of equipment available. But for the sake of discussion, let's say the equipment is made in the USA, UL or other NRTL listed, and rated for 240V 3?. The answer would then be yes, as 240/120V 3? 4W (high leg) supply is essentially the norm in the USA.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
If the equipment does not have a neutral, it shouldn't care what phase is the high leg. It will only see the phase to phase votlage and that will be the same no matter where the "high leg" is landed. The high leg is only an issue when you have line to netural loads.
 

Smart $

Esteemed Member
Location
Ohio
If the equipment does not have a neutral, it shouldn't care what phase is the high leg. It will only see the phase to phase votlage and that will be the same no matter where the "high leg" is landed. The high leg is only an issue when you have line to netural loads.
True. I know I read and understood no neutral in the OP, but my brain just completely sidestepped that fact when I posted my replies.
 

uwireme

Member
Location
Cottonwood, CA
If the equipment does not have a neutral, it shouldn't care what phase is the high leg. It will only see the phase to phase votlage and that will be the same no matter where the "high leg" is landed. The high leg is only an issue when you have line to netural loads.
That was my thought but what about getting shocked?
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
I hooked up a straight 3 phase no neutral wood working tool, called the manufacture to find out where to land the high leg and was told in the middle. Checked rotation no wire changing needed? all was good.

Got a call from the customer that some parts of the tool stopped working, manufacture came over and found high leg was not on the correct phase and told my customer he could have been shocked.

I have not talked to the manufacture yet but do some pieces of equipment require the high leg on a specific phase? And how could my customer be shocked by installing the high leg on a different phase?
You need to call the manufacture back and ask if any neutral load is required.
If not, then as has been mentioned, it doesn't matter where the high leg goes.

Most machine mfgs don't even take into consideration a high leg since they wouldn't know the transformer type a building might have.
Especially true if there are no neutral loads on the machine.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Engineer
You need to call the manufacture back and ask if any neutral load is required.
If not, then as has been mentioned, it doesn't matter where the high leg goes.

Most machine mfgs don't even take into consideration a high leg since they wouldn't know the transformer type a building might have.
Especially true if there are no neutral loads on the machine.
The only thing I can think of, if no nuetral is required, has to do with any internal filtering circuits that may be connected L-G. This wouldn't be the first time, some equipment manufctures used the ground as an intentional conductor.
 

uwireme

Member
Location
Cottonwood, CA
After sleeping on it...I think it may need a neutral but I did not see a place to land one.

If I need a neutral how do I make one off a rotary phase converter?
 

Smart $

Esteemed Member
Location
Ohio
But how do I make a neutral? Only 3 wires coming out of converter.
What converter? Sounds like a major detail not mentioned. So before speculating on a phase converter and/or providing a neutral, please tell us what is powering this tool...
 

Strathead

Senior Member
But how do I make a neutral? Only 3 wires coming out of converter.
I am thoroughly confused. Can you start over.

What is the nameplate voltage on the machine?
Why do you think it needs a neutral? I know that it does happen rarely, but typically industrial machinery that requires voltage other than the main operating voltage has a transformer to generate that voltage.
I would be especially suspect of a 240 volt rated system requiring a neutral. 208 less so.
Regardless of all of that, what would cause a shock hazard by failing to provide a neutral. I can think of other hazards, but unless there is a separate problem with the machine, there would, or should, be no way I can see a shock hazard.
 

kwired

Electron manager
Location
NE Nebraska
A rotary phase converter, single phase into converter and 3 phase no neutral out of converter
With a rotary phase converter the two input lines are directly tied to two of the output lines, the third "phase" is derived within the converter and will not be a reliable steady voltage and should only connect to motors. Any controls or other accessories that operate on straight 120 straight 240 or even 120/240 should be tied directly to the two lines that are also the input lines to the phase converter, and use neutral from the input source for any 120 volt loads. You are not really connecting the control circuit "through" the phase converter, just the input lines are "brought through" the phase converter and the third phase is derived within the converter.
 

Smart $

Esteemed Member
Location
Ohio
With a rotary phase converter the two input lines are directly tied to two of the output lines, the third "phase" is derived within the converter and will not be a reliable steady voltage and should only connect to motors. Any controls or other accessories that operate on straight 120 straight 240 or even 120/240 should be tied directly to the two lines that are also the input lines to the phase converter, and use neutral from the input source for any 120 volt loads. You are not really connecting the control circuit "through" the phase converter, just the input lines are "brought through" the phase converter and the third phase is derived within the converter.
If the tool is 3? 3-wire, any 120V controls or devices should be powered by a transformer in the tool.
 

kwired

Electron manager
Location
NE Nebraska
If the tool is 3? 3-wire, any 120V controls or devices should be powered by a transformer in the tool.
I agree. OP kind of changed what we were originally told when he threw in this phase converter and now we really don't know for sure just what he has. If he had 3? 3-wire supply, he would have no need for a phase converter, but would have a need for a transformer if 120 volt loads needed powered.
 

uwireme

Member
Location
Cottonwood, CA
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?
 
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