another grounded B phase thread

[kchap]

I just took a call from a customer who is installing a panel in a building with a grounded B phase service. The panel is rated for 240V AC, consisting of five 3-Phase VFD motor loads and the following single-phase loads:

• single-phase motor load connected to phases A - B
• single-phase motor load connected to phases A - C
• DC power supply connected to phases B - C
• heater load connected to phases A - B
• heater load connected to phases A - C

This is the first time I have even heard of a grounded B phase service. After studying on it for a little while, I am concerned about whether this panel is OK to connect to this type of service. The three-phase loads are fine, but I am not sure about the single-phase loads that connect to phase B.

Can anyone offer insight?

 

[LarryFine]

Any line-to-line (240v) load that does not require a neutral (120.240v) can use any two lines.

 

[Hv&Lv]

Any line-to-line (240v) load that does not require a neutral (120.240v) can use any two lines.

Wait. We talking about the same thing?
grounded b phase is a corner grounded delta.

Is it 480 delta or 240 delta?
There isn’t a center ground like an open delta or center grounded closed delta (high leg delta)

The op may have the naming wrong. He may have a center grounded delta.

 

[Dsg319]

Wait. We talking about the same thing?
grounded b phase is a corner grounded delta.

Is it 480 delta or 240 delta?
There isn’t a center ground like an open delta or center grounded closed delta

The op may have the naming wrong. He may have a center grounded delta.

For my sanity’s sake, line to neutral loads are not possible with a true corner grounded delta correct?

 

[Hv&Lv]

For my sanity’s sake, line to neutral loads are not possible with a true corner grounded delta correct?

Correct.
voltage L-L is 240 or 480,
but L-G voltages are 240(480), 240(480), 0(B phase to G)
And you can’t fuse the grounded b phase

 

[don_resqcapt19]

One thing that is often missed is the fact that the grounded phase is exactly that and the rules in Article 200 for the identification of that conductor apply.

In the field I have never seen a corner grounded system where the grounded conductor has bee identified as required in Article 200.

 

[Dsg319]

One thing that is often missed is the fact that the grounded phase is exactly that and the rules in Article 200 for the identification of that conductor apply.

In the field I have never seen a corner grounded system where the grounded conductor has bee identified as required in Article 200.

I was just thinking this in my mind. I remember a co-worker telling me a he came across a single phase 480v system. Maybe it was, but possible it was a corner grounded delta with a white/grey grounded conductor.

 

[Hv&Lv]

We don’t build corner grounded anymore unless the electrician AND owner signs for the installation.
We have way too many problems with people that don’t understand the installation.

I was just thinking this in my mind. I remember a co-worker telling me a he came across a single phase 480v system. Maybe it was, but possible it was a corner grounded delta with a white/grey grounded conductor.

There can only be two pole breakers for a three phase install. Electricians call us and say they have 0 volts on b phase when they are troubleshooting “something”, or they install three pole breakers and the ground is gone when the breaker trips.

 

[Tulsa Electrician]

I understood what Larry said as a load that needs a netutal.

 

[MTW]

Most VFD's will not like a corner grounded Delta supply, they are built to be applied on a Wye system.

 

[Tulsa Electrician]

Wonder if he meant a SDS and panel.
I have only installed one 480 v corner grounded service. Yes very very hard to get.

 

[synchro]

The document here from Schneider has some info about panels and breakers for corner grounded systems:

https://www.se.com/us/en/download/document/2700DB0202/

 

[Tulsa Electrician]

I find this interesting.
Read 2
Including the ground?

 

[jim dungar]

I find this interesting.
Read 2
Including the ground?

No.
Including the grounded conductor but not the grounding one. This is most commonly seen with motor circuits which employ commonly available 3 phase 3 pole equipment.

 

[Tulsa Electrician]

Maybe some one should let them know what it says. It was dated 2/2009 would be bad if some one read that and made a dangerous mistake.

 

[LarryFine]

For my sanity’s sake, line to neutral loads are not possible with a true corner grounded delta correct?

Technically, yes, as the grounded phase is treated like a neutral.

But, no to your question, as there is no grounded center tap.

It's merely a 3ph delta that happens to have one line intentionally grounded.

 

[LarryFine]

One thing that is often missed is the fact that the grounded phase is exactly that and the rules in Article 200 for the identification of that conductor apply.

In the field I have never seen a corner grounded system where the grounded conductor has bee identified as required in Article 200.

I have, complete with white wire and "dummy" fuses.

 

[LarryFine]

There can only be two pole breakers for a three phase install.

Not true. A 3p breaker can be used, because all poles open simultaneously.

 

[LarryFine]

No.
Including the grounded conductor but not the grounding one.

Agreed.

 

[Hv&Lv]

Not true. A 3p breaker can be used, because all poles open simultaneously.

I’m sorry if I was misleading. You are 100% technically correct.
But for troubleshooting it creates more trouble than it’s worth.
Like I stated earlier, it seems like every one we have built over the last 30 years we have had to send service guys to because someone didn’t understand what they were dealing with.
Those with two fuses (legal) or two poles didn't cause as much confusion as those with three pole breakers (also legal as you stated)