So 3 phase 240 volt has a high leg. 2 of the 3 legs measured to ground measure 120v. While the high leg to ground measures 240v to ground. So let’s say originally the unit was a 3 phase. Some time later some one put in a single phase unit 240v. Yes you have to be sure the wire gauge (awg) is sized for now the higher amp draw. But besides that if you chose one line and the high leg line to line measures 240v. Electrically when applied to a single phase 240v unit can it cause damage? I would guess no because it’s still 240v. But on the other hand I want to say yes because some how electrically its not the same. What is your experience on this?
So 3 phase 240 volt has a high leg. 2 of the 3 legs measured to ground measure 120v. While the high leg to ground measures 240v to ground. So let’s say originally the unit was a 3 phase. Some time later some one put in a single phase unit 240v. Yes you have to be sure the wire gauge (awg) is sized for now the higher amp draw. But besides that if you chose one line and the high leg line to line measures 240v. Electrically when applied to a single phase 240v unit can it cause damage? I would guess no because it’s still 240v. But on the other hand I want to say yes because some how electrically its not the same. What is your experience on this?
None. Never done this. I am in interested to read future posts.
usually high leg will run 165 170 to ground. I remember a cafe a few towns over that had central AC installed where the guy moved some breakers around. I had installed some counter top receptacles years earlier and the cook told me ever since the AC was put in one receptacle had more power in it. but they liked it cause the meat slicer worked way better in that one.
I would not use the "high leg" for single phase loads. Typically it's the B phase but code changes now allow for the C phase to be used. The high leg should be clearly marked in red or orange.
You can use the high leg on 240 volt single phase but can’t pull 120 volts off the high leg. The unit doesn’t care what the phase to ground voltage is.
You can use the high leg on 240 volt single phase but can’t pull 120 volts off the high leg. The unit doesn’t care what the phase to ground voltage is.
It's not phase to ground. It's phase to phase I believe the OP was referring to.
With a center tapped 120/240 delta system, the high-leg to ground should be close to 208 as was stated. Check your reading again, maybe with an analog meter to be sure, because that does not read kosher. If it is 240 call the poco.
And no way, do not, in my opinion, connect any equipment 240, or 208, phase to ground.
The equipment does see the amps and voltage, but sine waves are different phase to ground vs phase to phase. It could operate, but don't know how happy it would operate.
Pulling power from only one transformer of the bank could be a problem depending on the loading design.
That’s my point..... the unit doesn’t care what voltage you measure from phase to ground. It only cares what the phase to phase voltage is.
Yes and if you use the high leg for 1 of the phases and 1 of the two lower voltages for the second phase would you not have a imbalance between phases ?
Yes and if you use the high leg for 1 of the phases and 1 of the two lower voltages for the second phase would you not have a imbalance between phases ?
The way your wording this isn’t really right. I think you mean “legs” not “phases” as a single phase unit only uses 1 phase which is 1 transformer winding between 2 wires (or legs). As far as imbalance, you really can’t have an imbalance on a single phase unit that the unit sees. Now as far as the set of 3 phase transformers goes, it depends. It depends on the transformer setup, the sizes of the transformers, and whether it’s open or closed delta transformers. If there are 3 equally sized transformers on the poles wired in the closed delta configuration, then it doesn’t matter.
So 3 phase 240 volt has a high leg. 2 of the 3 legs measured to ground measure 120v. While the high leg to ground measures 240v to ground. So let’s say originally the unit was a 3 phase. Some time later some one put in a single phase unit 240v. Yes you have to be sure the wire gauge (awg) is sized for now the higher amp draw. But besides that if you chose one line and the high leg line to line measures 240v. Electrically when applied to a single phase 240v unit can it cause damage? I would guess no because it’s still 240v. But on the other hand I want to say yes because some how electrically its not the same. What is your experience on this?
R123 here's the original post and this is what I'm referring to.
In a building with the service configuration as you have described, it was common practice to put 120v loads on the A and C phase legs in panels that used blank outs where the B phase leg busbar was located, and only three phase loads could use the high leg in conjunction with the other two legs.
I would recommend avoiding using the high leg for any purpose without also using the other two legs in a 3-phase configuration for supplying power to the same appliance, so that all three legs have an even load.
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Yes, and that would be 240 volts which is outside of most 208/230 rated equipment.
208/230 volt is nominal voltage, not min and max. The voltage utilization range for 208/230 is something like 187-252 volts so 240 volts would be acceptable. If what you said was true, almost all residential equipment wouldn’t work in residences as they almost always have 240 volts single phase service and equipment is 208/230 on the nameplate.
ReplyOriginally Posted by anthonyac1
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