Corner Grounded Delta

[Misha80]

Could someone fill me in on the difference between a panel rated for a Grounded B Phase and a regular panel. I know it can't slash rated i.e. 120/240, but what else is different.

POCO approved my service upgrade to 3ph/4w, engineer came out several times and discussed it as I'm adding four services. They come out to change over my 3ph to the new service and inform me that they were mistaken, and all I can get is the corner grounded system. New panel is all fitted out and pretty, and I don't really want to change it.

Mick

 

[jim dungar]

First and foremost, you cannot supply 120V loads directly from a corner grounded system.

After that, you get into issues of circuit breaker fault ratings. Corner grounded system faults are much harder to interrupt, so UL Listing for these systems may mean a non-standard' test. Non-standard almost always means more money due to a limited market.

 

[kwired]

So who pays for their mistake? Did you or the owner have any agreements signed prior to you installing your equipment that possibly will not work? Is this engineer actually an engineer or just a POCO employee they call their engineer.

You and your customer got hosed.

 

[suemarkp]

An obvious difference is the phase to ground voltage is the same as phase to phase voltage. So all the things in the code allowing 150V or less to ground won't apply with this panel.

 

[Hv&Lv]

Could someone fill me in on the difference between a panel rated for a Grounded B Phase and a regular panel. I know it can't slash rated i.e. 120/240, but what else is different.

POCO approved my service upgrade to 3ph/4w, engineer came out several times and discussed it as I'm adding four services. They come out to change over my 3ph to the new service and inform me that they were mistaken, and all I can get is the corner grounded system. New panel is all fitted out and pretty, and I don't really want to change it.

Mick

Don't. Demand that they build you the bank you originally agreed to. Why should you or your customer have to change and pay for their mistake.
kwired is right. You probably talked to a service tech that works out of the engineering dept. "stakers" like to call themselves engineers, and hate to explain to the line superintendant that they wrote down the wrong assembly number and the construction crew built the wrong bank based on the build sheet or work order.

 

[Misha80]

Thanks for the replies.

I actually own half of the building that this service is for. I'm also doing service upgrades and panel replacements in the two adjoining buildings.

There are no signed documents with the poco, it's pretty laid back around here, I have to get a permit to do a service upgrade, but there are no inspections.

His card says engineer, but that's pretty meaningless.

I'm also finding out that this is all that's available in parts of this downtown area. The poles are complete rats nests, the one I'm tapped off of is actually leaning against my building, xformer over my rubber roof. The first time he came out he said they would replace it, as it was undersized for the load anyway, never happened so I called to actually put a ticket in for it. Engineer calls me the next day and tells me they don't have time to replace that pole, and that it's fine as it's not cracked, just leaning. I'll take a picture, it's obviously not fine.

I'm pretty fed up with them in general, but I'm also hesitant to raise an uproar as this "engineer" basically has final say in hooking up anything I install.

Regardless of what they do to resolve the situation in the near future, I need to get this service up now as it powers an elevator that needs to be up asap.

I guess what I'm asking is this. I replaced the B phase fuse in the disco with a solid bar, if my ocpd's all have a high enough interrupt rating, is there any problem using a standard panel until the service is upgraded? As I said, I am part owner of the building, but doing the upgrade as a bid job with a contract, I don't mind running a bit afoul of code until the upgrade, but I don't want to do anything unsafe.

.

Mick

 

[TobyD]

What voltage rating did you originally have on your building?Did you go from 120/240 single phase?Are you saying that now the POCO is suppling you with a HIGH leg on the B phase?Where are you located?Just trying to understand a little more .I just finished 2 service entrance pulls with a similiar issue.But, the POCO backed up and built the bank as first agreed upon.

 

[ptonsparky]

Corner ground would give you 240v to ground on 2 phases and 0 volts to ground on the third. No 120v available. You could install your own delta to wye transfomer if POCO is not going to deliver what you asked for.

Hi leg delta would give you 120 to ground on 2 phases and roughly 212 on the third.

Which system are they providing?

 

[renosteinke]

"The transformer over my roof ...." THERE's the problem.

Let me put it in simple terms .....

IF single-phase service requires one transformer, one might speculate that three phase service needs three transformers. You would be wrong.

If there were three transformers, the PoCo could give you a proper "Wye" system with little problem; just connect the wires differently. So, why do they persist in delivering 'delta' arrangements?

Well, if they limit what you can do, it can be cheaper for them. With an ordinary 'wye' system, they need three big transformers. If they can get you to accept a 'delta,' they can use two small transformers, and just one larger transformer for the 120 loads.

An even more economical (for them) is the 'open delta' arrangement, where they need only two transformers. One big and one small.

What about 'corner grounded' deltas that are also 'open'? Now it gets even cheesier. If there is no need for 120 circuits, they can make a 'corner grounded' system using only two small transformers.

Look at your power pole. There ought to be three or four wires WAY high up, another three or four wires at transformer level, and the phone / cable wires even lower down. If this is your arrangement, there ought to be no big deal getting proper three phase power to you.

If the real high wires are missing, then the PoCo has not brought all three phases down your street. Now it becomes a bit more expensive for them to get you the power you want - they essentially need to replace everything back to the main line or substation. That's why they try to cut corners.

The bottom line is that it might be easier for you to relocate than to pay for the new service.

 

[al hildenbrand]

POCO approved my service upgrade to 3ph/4w, engineer came out several times and discussed it as I'm adding four services. They come out to change over my 3ph to the new service and inform me that they were mistaken, and all I can get is the corner grounded system.

I actually own half of the building that this service is for. I'm also doing service upgrades and panel replacements in the two adjoining buildings.

There are no signed documents with the poco, it's pretty laid back around here, I have to get a permit to do a service upgrade, but there are no inspections.

I'm also finding out that this is all that's available in parts of this downtown area. The poles are complete rats nests, the one I'm tapped off of is actually leaning against my building, xformer over my rubber roof. . . .

Mick,

Are you (and those you are upgrading) the only customers supplied by the transformer bank leaning over your roof?

Given that this is a "downtown area" the PoCo may have realized, after the first approval, that it has to set a whole new pole and transformer bank to supply you, leaving the old bank to supply those other customers in the area.

 

[jim dungar]

Hi leg delta would give you 120 to ground on 2 phases and roughly 212 on the third.

The high leg is nominal 208V.
Right angle triangle, hypotenuse = 240V and the short leg =120V therefore, according to Pythagoras, the 'high' leg =208V.
Of course, any real time voltage measurement may be different.

 

[kwired]

"The transformer over my roof ...." THERE's the problem.

Let me put it in simple terms .....

IF single-phase service requires one transformer, one might speculate that three phase service needs three transformers. You would be wrong.

If there were three transformers, the PoCo could give you a proper "Wye" system with little problem; just connect the wires differently. So, why do they persist in delivering 'delta' arrangements?

Well, if they limit what you can do, it can be cheaper for them. With an ordinary 'wye' system, they need three big transformers. If they can get you to accept a 'delta,' they can use two small transformers, and just one larger transformer for the 120 loads.

An even more economical (for them) is the 'open delta' arrangement, where they need only two transformers. One big and one small.

What about 'corner grounded' deltas that are also 'open'? Now it gets even cheesier. If there is no need for 120 circuits, they can make a 'corner grounded' system using only two small transformers.

Look at your power pole. There ought to be three or four wires WAY high up, another three or four wires at transformer level, and the phone / cable wires even lower down. If this is your arrangement, there ought to be no big deal getting proper three phase power to you.

If the real high wires are missing, then the PoCo has not brought all three phases down your street. Now it becomes a bit more expensive for them to get you the power you want - they essentially need to replace everything back to the main line or substation. That's why they try to cut corners.

The bottom line is that it might be easier for you to relocate than to pay for the new service.

I see his problem as being an older developed area that already has a mess in the alley that the POCO does not wish to try to clean up leaving him with only one system choice - the one that is existing.

He probably still can get anything he wants but POCO will set what price he can get it for. Hopefully they have enough available capacity for what ever load he proposes to place on it, he can always transform voltages with his own equipment but can never use more than they can deliver.

 

[Misha80]

The transformer hanging over the roof provides single phase service.

It's set up like this, there are two 3ph banks, one half a block east, and one half a block west. The one to the east supplies me and 2 other customers, the one to the west looks to supply 3 as well, one being city hall. There are single and three phase secondaries strung between each pole. There are primaries running on the very top.

I want them to replace my leaning pole and install a wye bank. To do that they have to also relocate the single transformer. I guess my argument is if not now when? Will this whole area be limited to this delta system forever, and no new renovations or buildings will be able to get anything else?

I'm sure they would build the bank if I want to pay for it..but like someone said, I installed equipment for the service I was promised, I wouldn't have even done this upgrade if I had known I couldn't get the system I wanted.

Also it's a corner grounded delta, not a delta with a high leg. I have 0V B phase to ground. Interestingly enough, they marked the grounded phase Orange, tell me that's not a recipe for disaster....

Mick

 

[ptonsparky]

I believe orange is used for the grounded leg by POCOs. One of the utility guys may step in and verify or deny. Hopefully.

 

[ptonsparky]

The high leg is nominal 208V.
Right angle triangle, hypotenuse = 240V and the short leg =120V therefore, according to Pythagoras, the 'high' leg =208V.
Of course, any real time voltage measurement may be different.

I thought it was sq rt of 3 * 120v , in this case. I don't think I have ever seen 208. Only 1 of 6 meters has ever been calibrated, as far as that goes so...that argument doesn't hold water.

 

[jim dungar]

I don't think I have ever seen 208. Only 1 of 6 meters has ever been calibrated, as far as that goes so...that argument doesn't hold water.

If you are referring to a nominal 240V L-L (per the NEC), then you must also refer to the high-leg as a nominal 208V L-N (allowing for rounding).

And yes the ratio of 208V to 120V is approximately 1.732 (sqrt 3).

 

[kwired]

I thought it was sq rt of 3 * 120v , in this case. I don't think I have ever seen 208. Only 1 of 6 meters has ever been calibrated, as far as that goes so...that argument doesn't hold water.

I can't recall ever seeing 208 volt reading myself but on same systems the 120 reading was also at least 123 - 125 which will bring line - line up to 213-217.

 

[Hv&Lv]

I believe orange is used for the grounded leg by POCOs. One of the utility guys may step in and verify or deny. Hopefully.

I wish it was standard in the NESC. I prefer orange for a high leg only and the grounded conductor of a corner grounded delta to be white. It makes life so much easier when you have to rebuild a bank that is laying on the ground destroyed or "cleaned up" by a groundman that doesn't know of forgot what to look for before he removes the connections from the XF.

 

[hardworkingstiff]

Wow, I've been in electrical work since 1973 and I've never seen nor heard of the PoCo delivering a corner grounded Delta service. I'll say it again, wow!

Now, as far as the high leg on the 3-phase Delta High leg, it used to be 190-volts (in the Norfolk, VA area) back in the early '70s, but that was when they delivered 110/220. When they went to 120/240 the high leg went to 208 (just like the math says it should).

Again, wow on the corner grounded delta service.

What advantage is it to the PoCo to deliver this type of service (which causes headaches for the user).

 

[ptonsparky]

We see them often enough, mostly existing for irrigation. The 480 gounded deltas make me nervous. More than usual anyway.