240/120 3ph.

[Open Neutral]

So I'm still working with a NorCal property owner needing service to an upcoming house & pool.

We'd really like 3ph 208/120 wye; for a welder & a number of pumps: deep well, swimming pool/slides, and fire protection. The rub is, the house is 750 ft back crow-fly from the 3ph-221.5 kv pole line & PG&E wants a 1400 ft long route. PG&E has guesstimated $60k for that, and quoted us only (!!!) $29K for split phase 320A 240/120.

I gather that a large part of the $60K is that 3-ph is considered 'Special Facilities' & such is heavily marked up under Rule 2. [This is part of the muddle; I was told by Engineering that a 7.5+ HP motor would take us out of Special Facilities, but the lower level people disagree.]

However, we recently found out several details they had, well... I'll just say 'overlooked' telling us, and as a result we had a meeting with them. Now it seems we can use so-called 'Applicant-Installation Options' instead of paying them for much of the work.

(While they insist such an approach is only advantageous to developers who can't wait for their crews to install; I'm twice-shy & waiting for some outside estimates on that approach.)

But the kicker was added on at the very end. While 3ph 208/120Y would be a Special Facility; 3ph 240/120 would not. I can't recall the term I've seen used here, but this appears to be their delta service with one 240 err side center-tapped & grounded; 120V loads would come both directions off it alone. Yes, it's mentioned in their Green Book, at least in section 5-13.

My questions for the brain trust here..

1) Why would they *want* to offer that to us? It's just a different transformer secondary to them, right?

2) Can we stomach it?

Yes, all the 120 loads can be put on the one side; both halves.

We have one 3-ph 480 load [Don't ask...] already in place; I'd assume I can buy a 240:480 transformer as easily as a 208:480 one.

We could, I hope, buy 3ph motors rated for 208/240 or just 240.

But is it legal to run 240V single phase loads off the other two sides? That would mean they would be 120 & 360V above ground.

Or do we buy our own 240:208Y transformer? That makes sense from an initial purchase (to avoid the $pecial Facilitie$ standing) but at an efficiency cost.

 

[augie47]

So I'm still working with a NorCal property owner needing service to an upcoming house & pool.

We'd really like 3ph 208/120 wye; for a welder & a number of pumps: deep well, swimming pool/slides, and fire protection. The rub is, the house is 750 ft back crow-fly from the 3ph-221.5 kv pole line & PG&E wants a 1400 ft long route. PG&E has guesstimated $60k for that, and quoted us only (!!!) $29K for split phase 320A 240/120.

I gather that a large part of the $60K is that 3-ph is considered 'Special Facilities' & such is heavily marked up under Rule 2. [This is part of the muddle; I was told by Engineering that a 7.5+ HP motor would take us out of Special Facilities, but the lower level people disagree.]

However, we recently found out several details they had, well... I'll just say 'overlooked' telling us, and as a result we had a meeting with them. Now it seems we can use so-called 'Applicant-Installation Options' instead of paying them for much of the work.

(While they insist such an approach is only advantageous to developers who can't wait for their crews to install; I'm twice-shy & waiting for some outside estimates on that approach.)

But the kicker was added on at the very end. While 3ph 208/120Y would be a Special Facility; 3ph 240/120 would not. I can't recall the term I've seen used here, but this appears to be their delta service with one 240 err side center-tapped & grounded; 120V loads would come both directions off it alone. Yes, it's mentioned in their Green Book, at least in section 5-13.

My questions for the brain trust here..

1) Why would they *want* to offer that to us? It's just a different transformer secondary to them, right? .

Depending on their supply, sometimes it is easier (cheaper) for them to supply 240/120 3 phase high-leg

2) Can we stomach it?

Yes, all the 120 loads can be put on the one side; both halves.

We have one 3-ph 480 load [Don't ask...] already in place; I'd assume I can buy a 240:480 transformer as easily as a 208:480 one. .

Yes

We could, I hope, buy 3ph motors rated for 208/240 or just 240. .

NOrmally

But is it legal to run 240V single phase loads off the other two sides? That would mean they would be 120 & 360V above ground. .

No problem. You just need to be sure and not use 240/120 slash-rated breakers when "B" is being used. You need straight rated 240 which are more expensive (see 240.85)

Or do we buy our own 240:208Y transformer? That makes sense from an initial purchase (to avoid the $pecial Facilitie$ standing) but at an efficiency cost.

I see no need... 240/120 3 phase used to be common for installations with "light" 3 phase loads relative to the single phase loads.

 

[Open Neutral]

Depending on their supply, sometimes it is easier (cheaper) for them to supply 240/120 3 phase high-leg

Their supply is their overhead '4ART' 3ph 21kv primary; they'll run 1/0 EPR CONC ENCAP PE to their transformer at the house.

No problem. You just need to be sure and not use 240/120 slash-rated breakers when "B" is being used. You need straight rated 240 which are more expensive (see 240.85)

But what about the appliances? Will the manufacturers & the AHJ agree the 208/240 oven, range etc. are OK with being run 120/360, so to speak?

 

[Open Neutral]

Make that:

....with being run 120<->360, so to speak?

 

[augie47]

240 volt appliances will operate the same on a hi-leg delta system a a single phase 240 system but you need to use extreme caution on appliances with neutral terminations due to the high leg.

 

[Smart $]

...
But what about the appliances? Will the manufacturers & the AHJ agree the 208/240 oven, range etc. are OK with being run 120/360, so to speak?

There is no 360.

Line A is 120V to neutral/ground
Line B is 208V to neutral/ground
Line C is 120V to neutral/ground

All Line to Line is 240V.

You can use A-B and B-C for 2-pole 240V 1? 2W loads (keeping slash rated breakers as Gus mentioned out of the picture).

 

[lefty]

Phase to Phase

Phase to Phase

I hope somebody can explain it better than I can, but here goes. Voltage between any of the phases are 240volts. You do not have 360volts. The 120volts is center tapped between two phases A and C for example. This center tap causes the B Phase to be approxiamatly 208volts to ground, just do not use B Phase for single pole 120volt loads, there will be to high of a voltage for this. Use B Phase for loads that need two or three poles and you will be fine. I hope somebody will chime in, there are some on here that can explain there way out of anything.:lol:

 

[lefty]

Somebody beat me to it.

Somebody beat me to it.

They already beat me to the answer:slaphead:

 

[Open Neutral]

There is no 360.

Line A is 120V to neutral/ground
Line B is 208V to neutral/ground
Line C is 120V to neutral/ground

All Line to Line is 240V.

You can use A-B and B-C for 2-pole 240V 1? 2W loads (keeping slash rated breakers as Gus mentioned out of the picture).

  B

A g C

You are correct; I was not thinking far enough in. (Memories: Prof. Klingshirn would give me one of his looks and I'd skulk back in shame to read that chapter all over again...)

So any 240-only appliance should be OK on AB or BC legs. The 240/120V ones are a different matter. [Hmm; are there any 240-only clothes dryers in the US?]

This might actually work...if the AHJ does not have kittens.

 

[broadgage]

Three phase delta at 120/240 volt should be fine.
Many appliances that are listed for both 208 and 240 volt operation will perform better on 240 volts.
As others post, there wont be 360 volts anywhere.

If all 3 transformers are of equal size, then take care not to overload the 120/240 volt one. All 120 volt loads, and loads that need a 3 wire 120/240 volt supply MUST be on this transformer.
Therefore straight 240 volt loads should be on the other transformers.

If on the other hand, the 120/240 volt transformer is larger as is sometimes the case, then most of the load should be on that one, with the other phases only utilised for 3 phase loads.

Although 208 volts is present between the neutral and the high leg, such services are not primarily intended for 208 volt loads.
Most 208 volt loads are also suited for 240 volt.
Some consider that 208 volt loads may be utilised, between high leg and neutral provided that such loads are a small proportion of the service capacity.

 

[Open Neutral]

I don't know if PG&E will propose one 3ph or three single-phase units. We have to pay up front before we get specifics. Every other mention of 3ph transformers, pole or pad, has been one transformer.

Looking in their GreenBook, they list multiple pad-mount 3ph units with 120/240 secondaries, such as the 261547.

I'm still befuddled as to why they would rate 208 Wye as Special Facilities, but 240 Delta is not....

 

[kingpb]

If the cost for the High leg delta is $29K, and the cost for the 3ph 208Y/120V is $60K the additional cast is around $30K, It sounds like the place you are building is upscale in nature, I wouldn't think the Owner is really going to care much about the $30K. I would assume the higher cost is simply because of where (distance) they have to bring a line in from that has 3ph capability.

 

[ptonsparky]

In the past these high leg delta systems would/could use only two transformers, not three, which would reduce the cost even more for the POCO. Pole top.

 

[kwired]

They can provide an open delta supply cheaper than a full delta or wye because they only need to supply it with two phases and a neutral. They can build it out of any combination of single phase transformers they have on hand also. They can do so with single phase padmounts also - not done as often but it can be done.

 

[broadgage]

To supply three phase at utilisation voltage requires a three phase source.

Open delta requires only 2 transformers to be purchased rather than 3 thereby saving money, but it still requires a 3 phase source.

If the utility are going to supply 2 single phase transformers for 3 phase open delta service, or if they are going to use 3 single phase transformers for 3 phase closed delta dervice, then you need to know the size of the transformers to ensure that no transformer will be overloaded.

If a 3 phase transformer is to be supplied, then simply ensure that the load is reasonably balanced.

 

[Open Neutral]

OK, I'm still reading up & looking for drawings, but infer if we were to be offered open delta, the one transformer would have a centertap secondary that's the neutral. [I find lots of open delta drawings but none showing the tap to get 120 service.]

Further, if we assume the windings are A-B & A-C, with B-C open;

  B

A g C

it sounds like we should not be loading B-C with single phase 240v loads. We can live with that as well.

But in talking to a veteran contractor who does large and small "Option 2" PG&E jobs, and whose company is all PG&E err escapees; he is very surprised that they are offering, much less suggesting, 240/120 3ph. He thought it was history. He recalled open delta as something they offered for agricultural use, but in teh 70's.

I do note that I can't find a mention of "open delta" in the PG&E Green Book; they do show a closed delta configuration.

 

[Smart $]

...

I do note that I can't find a mention of "open delta" in the PG&E Green Book; they do show a closed delta configuration.

Didn't you say earlier the xfmr was going to be pad mounted? I have to wonder if there even is an open delta pad mount in a single unit, and I certainly can't imagine the POCO doing a two unit pad mount installation. In my mind open delta pad mount is n/a.

 

[kwired]

Didn't you say earlier the xfmr was going to be pad mounted? I have to wonder if there even is an open delta pad mount in a single unit, and I certainly can't imagine the POCO doing a two unit pad mount installation. In my mind open delta pad mount is n/a.

I would guess two unit pad mount cost less or at least about same and you will not have to wait for it to be manufactured.

 

[Smart $]

I would guess two unit pad mount cost less or at least about same and you will not have to wait for it to be manufactured.

Quite likely.


But I'm doubtful the POCO would consider such for the OP's installation.

 

[Open Neutral]

I don't know if it *is* open delta; I'm going to reach out to their transformer expert & see what he says.

Of course, if it's closed delta, that just furthers my confusion as to why a wye installation is Special Facilities but a delta is not.