Delta High "B" phase

[ACFIXR]

This is a first for me today.....Got befuddled by my meter readings which usually means my batteries are almost dead or there are no grounds. I needed some temp power to charge my batteries (listen to radio)so i flip up a disco door and tie in my trusty pigtail.After a few minutes of getting a good ground I finally got some juice. But my readings were weird.....208v A-B,208v A-C, 110v-A-Ground, 110v C- ground and 152v B- ground. 152 volts what the heck is that?

The panels show this diagram-



It shows 208 to ground. Is a transformer going out?

[timebuilder]

No, it's normal for many transformer configurations.

A "high B," "wild leg," or "bastard leg" is a holdover from days when a transformer used a ground connection in the middle of one of the windings, changing the relationship between that ground connection and the opposite leg, usually the B. You can see it on the diagram you posted.

The B leg gets marked orange, and lives in the second position of the panelboard. Today, there is a notice placed on the deadfront of the panelboard cabinet that warns against using the B leg to ground, because of the higher voltage.

Some older panels actually skip the B leg, and there is a blank out used in place of a breaker, when the three phase is feeding a panel for 120V single phase loads.

[ascj]

Wow, never seen a 208v 3 phase four wire delta. Always, thought it was only 240v?

[ACFIXR]

Thanks Timebuilder.

I wonder if there are any extra considerations for fusing and or grounding with disconnects on circuits out of these panels. For example does anything weird happen if you lose the "c" phase? Would theses Delta panels be more easily able to be out of "balance"? Everything I do now days and for many years has been 460v volt "Y" and the voltages have been up to 495v at times. I hate 208 because units lose alot of their "potential" capacity because of the low voltage. A 460v unit running on almost 500v screams..............

[hvacrmedic]

It doesn't add up. If you have 208 volts between phases, then the hi leg should read around 180 volts to ground. You should also get 104 volts from A or C to ground. What did you get between B and C?

[RuralSpaceman]

In case your customer might like to add a variable frequency drive one day... make sure everyone understands the system is a "corner grounded, delta system" and follow the VFD installation instructions.

Or you might be buying more than just one drive.

[controldude]

The wild leg voltage will vary by manufacturer it is all in where they ground the phase at the transformer.

[R123]

In case your customer might like to add a variable frequency drive one day... make sure everyone understands the system is a "corner grounded, delta system" and follow the VFD installation instructions.

Or you might be buying more than just one drive.

This is not a "corner grounded delta system". A corner grounded delta system has 1 leg grounded which would read 240 volts across all 3 phases and reads 240 volts to ground on 2 phases and 0 volts to ground on the third phase. There is no center tap for 120 volts.

This system is called "center tap delta".

[wolfdog]

This is not a "corner grounded delta system". A corner grounded delta system has 1 leg grounded which would read 240 volts across all 3 phases and reads 240 volts to ground on 2 phases and 0 volts to ground on the third phase. There is no center tap for 120 volts.

This system is called "center tap delta".

And...

"Corner grounded delta" does not have a neutral, that is why one phase is grounded to stabilize the sytem.
The 240 delta in the original post has a neutral that is derived by the center tapped winding.....and that causes the high leg.

[DPinst]

Corner ground !!!
That is the first explanation of this voltage reading that make some sense.
Have had some older buildings that you read your meter and have to take a second look because you do not believe your meter.

Thank you R123

[wolfdog]

An earlier post stated that 240 delta was a holdover from the old days. It is actually quite common depending on the application.
In this area:
240 delta is used where the 3 phase load is high is relation to the single phase load, the motors like the higher voltage.
208/120 is used where the 3 phase load is present but not predominant. The single phase balances out better.

[timebuilder]

Thanks Timebuilder.

I wonder if there are any extra considerations for fusing and or grounding with disconnects on circuits out of these panels. For example does anything weird happen if you lose the "c" phase? Would theses Delta panels be more easily able to be out of "balance"? Everything I do now days and for many years has been 460v volt "Y" and the voltages have been up to 495v at times. I hate 208 because units lose alot of their "potential" capacity because of the low voltage. A 460v unit running on almost 500v screams..............

I know what you mean. I have a whole warehouse roof in philly that runs 498 volts!

[timebuilder]

An earlier post stated that 240 delta was a holdover from the old days. It is actually quite common depending on the application.
In this area:
240 delta is used where the 3 phase load is high is relation to the single phase load, the motors like the higher voltage.
208/120 is used where the 3 phase load is present but not predominant. The single phase balances out better.

The center tapped delta IS a holdover from the old days. All of the panels in buildings that use the center tapped delta system are almost as old as I am. The buildings themselves are from the 20's and 30's.

ALL of the new construction three phase systems I see are wired without the center tap, and all phases measure the same voltage when referencing ground. In fact, our utility will not supply a new building using anything but a full three phase drop. You can always tell the full delta service from the three transformers on the pole.