( C ) phase is 240 V. to ground

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Buck Parrish

Senior Member
Location
NC & IN
Which three way system has (A) phase 120 to neutral (B) phase 120 to neutral (C) phase 240 volts to neutral ?

That's what I've got at a fish farm I'm working on.
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
It's probably more like 208 to ground and would be a center grounded Delta.

Roger
 

Buck Parrish

Senior Member
Location
NC & IN
They've got printed signs on all the panels . ' C phase 240 volts to ground.
So I took the cover off and put my meter on it. They've got orange tape on C phase and sure enough it's 240 to ground. 240 between A and B
 

Dennis Alwon

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Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
You have a high leg delta system. Do not hook any 120V circuits to the high leg. You still should have 240V between phases
 

qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
Occupation
Sorta retired........
Shouldn't it be on B phase?

It should be, but the POCO often doesn't want it on B phase in their equipment.
Once it came in it could have been put back on B but most just leave it on C because that's where it started out.
 

Buck Parrish

Senior Member
Location
NC & IN
Okay , thanks.

Yes if you changed it now. The motors might go backward. Then their would be Talapia flopping all over the floors. I'm putting lights over the center of the indoor fish pools. The water is five feet deep.
 

don_resqcapt19

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Location
Illinois
Occupation
retired electrician
They've got printed signs on all the panels . ' C phase 240 volts to ground.
So I took the cover off and put my meter on it. They've got orange tape on C phase and sure enough it's 240 to ground. 240 between A and B
It is not mathematically possible for the high leg to be 240 to ground where the phase to phase voltage is 240 and two of the legs are 120 to ground.
 

kwired

Electron manager
Location
NE Nebraska
I am having a deja vu...
same here.

Don't recall ever resolving the other similar problem.

Buck Parrish did you measure with a meter or with a Wiggy or other similar device?

If it is a 240 volt nominal system with a high leg - it is not possible to have 120 volts to ground on the other two phases if the high leg is 240 on a healthy properly working system. If the high leg is 240 it will bring the other two phases up to about 138 volts and line to line voltage to about 276 volts. In order to maintain the phase angles voltages must be in right proportions or something abnormal is going on.

But if the overall system voltage is reading a little high and you are testing with a Wiggy or similar device you may see 125 to ground and 216 on the high leg which could make some voltage testers indicate 240 instead of 208.
 

Carultch

Senior Member
Location
Massachusetts
Shouldn't it be on B phase?

The convention has changed over time. Today, the rule is to put it on the B phase.

Years ago, it was on the C phase, and when it changed to the B-phase, a lot of utilities said "we're not changing our standard just because you changed yours". So on metering equipment it may be on the C-phase, while on all downstream equipment it would be on the B-phase.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
150422-1526 EDT

Buck:

You have made insufficient measurements. Suppose this was to be a three phase wild leg delta using two transformers. One transformer is center tapped providing 120-0-120, and the other is just 240. But if one end of the 240 was connected to neutral instead of one of the outer ends of the center tapped winding, then the result would be what you read. I doubt you have a phase sensitive meter.

You also need to measure all three leg-to-leg voltages. If my assumption is correct, then one of the unmeasured values would be about 208 and the other 317.

.
 

kwired

Electron manager
Location
NE Nebraska
150422-1526 EDT

Buck:

You have made insufficient measurements. Suppose this was to be a three phase wild leg delta using two transformers. One transformer is center tapped providing 120-0-120, and the other is just 240. But if one end of the 240 was connected to neutral instead of one of the outer ends of the center tapped winding, then the result would be what you read. I doubt you have a phase sensitive meter.

You also need to measure all three leg-to-leg voltages. If my assumption is correct, then one of the unmeasured values would be about 208 and the other 317.

.
What do you suppose the chances are of encountering that on something that has been in service and operation - which I guess he didn't specify but sort of seems to be that this is something he just stumbled onto that was already there.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
150423-1055 EDT

kwired:

I was just looking for a possible way to explain his readings. With two more measurements of voltage we may be able to determine what the source looks like. What transformers are on the pole would be useful to know and how they are wired.

He noted that there was a tag indicating 240 V. Also I assume he is using a meter with reasonably good accuracy.

Another possibility is a single phase system with one leg 240 to neutral plus the center tapped 120-0-120 secondary.

.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
150423-1055 EDT

kwired:

I was just looking for a possible way to explain his readings. With two more measurements of voltage we may be able to determine what the source looks like. What transformers are on the pole would be useful to know and how they are wired.

He noted that there was a tag indicating 240 V. Also I assume he is using a meter with reasonably good accuracy.

Another possibility is a single phase system with one leg 240 to neutral plus the center tapped 120-0-120 secondary.

.

We went through all these scenarios in that other thread. The readings as they are reported cannot be correct.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
We went through all these scenarios in that other thread. The readings as they are reported cannot be correct.

One possibility that has not been considered is RMS voltage readings on a source with extremely high third harmonic voltage components.
But it would be coincidental that the odd voltage came out so close to an exact 240V.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
150423-1300 EDT

ggunn:

What other thread?

In post 15 here I provided a possible way to get his measurements. Was this suggested in the other thread?

.
 
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