On Thu, 12 Feb 2004 14:37:36 GMT Beachcomber wrote: | On 12 Feb 2004 08:51:03 GMT, snipped-for-privacy@ipal.net wrote:>
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|>A-----*------------------------------------------------------* |>B-----|--------------*----* | |>C-----|--------------|----|--------------*----* | |>N--* | | | | | | |> | | 208 | | 208 | | 208 | |> | \/\/\/\/\/\/\/ \/\/\/\/\/\/\/ \/\/\/\/\/\/\/ |> | ================= ================= ================= |> | /\/\/\/\ /\/\/\/\ /\/\/\/\ /\/\/\/\ /\/\/\/\ /\/\/\/\ |> | | 120 | 120 | | 120 | 120 | | 120 | 120 | |> | *--------|--------|-|--------|--------|-|--------|--------|-- X1 |> | | | *--------|--------|-|--------|--------|-- Y1 |> | | | | | *--------|--------|-- Z1 |> *----------*--------|----------*--------|----------*--------|-- N |> *-------------------|-------------------|-- X2 |> *-------------------|-- Y2 |> *-- Z2 |>
| Phil: | Thanks for a most impressive diagram. Now I'm wondering if I can | just order my service this way from the power company. (In other | words... they would configure the secondaries according to your | diagram, using a primary voltage of whatever the incoming lines are | set for... | | I've not seen a diagram like this before. Would this be considered a | standard class of service? The only thing that causes me to have | concern about your circuit is that I've lived in condo buildings that | only provided the common wye 208/120 V. (single phase service to each | unit - 3-phase incoming service). I'm now wondering why I could not | get the more desirable 240/120 V. service (as per your diagram).
The power company would likely not deliver 7 wire service to you. They don't have meters that can work with 7 wires. And if they did this with
3 separate 1 phase meters, they likely can't set that up under a single service account. And then there are electrical code and tariff issues.
To meter it properly, it will have to be brought in as conventional
3 phase. You'll have to put in three transformers, or if you can find such a thing (I've never seen one, and I've seen a lot of transformers listed by manufacturers and used/surplus sellers), a 6-pole 7-wire
3x240/120 3 phase transformer (let me know if you find such a beast).
I also recall seeing some limitations on number of wires on a service drop.
3 phase can be run from 3 separate transformers. The power companies do it all the time. Just look around at the poles in commercial areas and you'll see many with 3 transformers (pole pigs) together. Look closer (from the ground) and see how it is wired. You should see one of the wires going to all three on the secondary terminals, and three (for delta service) or four (for wye service, the most common) wires going into the drop (overhead or underground).
So what you'll likely end up with is normal 3 phase power at some voltage. How you wire this up will depend on which voltage you get.
If you get service at 208Y/120, you can wire the hot tubs up as shown above, with transformers rated for the usage you will have (including any future expansion) for those hot tubs. Then lights and outlets in the rest of the place can just tap off of the 208Y/120 directly.
Alternatively, you can run the entire building/office/whatever from those transformers. Each of the 240/120 volt outputs would need their own breaker panel whether just for the hot tubs or for the whole area.
If your service comes in at 480Y/277 (or 600Y/347 in Canada), you have to have either a 3 phase transformer, or three 1 phase transformers, just to get usable 120 volts circuits, anyway. In these cases, you might as well just do the above circuit for the whole place and have
240/120 (x3) everywhere.
If you are going with 3 transformers as described above for the whole building/office/area, then you might try to get your service dropped in at 240 volt DELTA (if not the higher voltages listed above). The reason for that is because single phase transformers with an input of 240 volts or 480 volts (usually they come as dual primary 480/240) are cheaper due to mass production.
If you get 240 DELTA, you won't have a neutral coming in, but you'll be creating one on the secondaries (you _must_ run everything from the transformers with this kind of power service). Of course that neutral must be well grounded from the power room where the transformers will be located.
You might also be able to get the oddball power service of 416Y/240 which might be known as 400Y/230, etc. It's uncommon in the US, but not unheard of. The reason it might be possible is because a regular
240/120 volt secondary pole pig can be easily wired up to do it in a WYE configuration by ignoring the center tap. If you do get this kind of service, the wiring diagram I provided will have to be changed to following to be able to use the cheaper transformers:
A-----* B-----|-------------------* C-----|-------------------|-------------------* N--*--|--------------*----|--------------*----|--------------* | | 240 | | 240 | | 240 | | \/\/\/\/\/\/\/ \/\/\/\/\/\/\/ \/\/\/\/\/\/\/ | ================= ================= ================= | /\/\/\/\ /\/\/\/\ /\/\/\/\ /\/\/\/\ /\/\/\/\ /\/\/\/\ | | 120 | 120 | | 120 | 120 | | 120 | 120 | | *--------|--------|-|--------|--------|-|--------|--------|-- X1 | | | *--------|--------|-|--------|--------|-- Y1 | | | | | *--------|--------|-- Z1 *----------*--------|----------*--------|----------*--------|-- N *-------------------|-------------------|-- X2 *-------------------|-- Y2 *-- Z2
If you do get 416Y/240 you can also use the original diagram with 416 volt input transformers, but those are rare and more expensive. There is no reason to get 416Y/240 unless it saves you money (it's uncommon and probably not available just because no one uses it anymore).
Check your power company web site for tariffs to see what you might be able to get.
And of course, a licensed electrician will have to install this and make sure it meets all applicable code, and it will have to be inspected in any scenario. All I'm doing is exploring your options (something I would be doing if I were installing all this). I don't like running
240 equipment on 208 volts ... I've seen it burn out to many A/C motors.
| Are you saying there is no issue with the three center tapped neutrals | all bonded together like that? It would seem that even with no load, | you would have current flowing in the neutral even though it might all | sum to zero.
You would have no current in the neutrals unless the transformers were faulty. If you have current flowing _out_ of the transformer on one wire you have to have current flowing _in_ on another. That's how ground fault breakers are able to work without cutting into the ground wire. What they do is measure the current on all the hot wires and neutral (not ground) wire together (i.e. run them all through a common current transformer). If there is a ground fault and current is flowing out the ground (green) wire somewhere, then the vector sum of currents in the hots+neutral will show such current flowing (and trip the breaker at the appropriate level). If there is no ground leakage, that sum of hots+neutral would be zero.
If you do have potential between transformer secondaries, you have a big problem.
Just be sure you put GFCI breakers on all the circuits going anywhere near the hot tubs, bathrooms, kitchens, concrete floor areas, etc. The codes should spell out all these requirements and your electrician should know them well (I'm not an electrician and I'm assuming you are not, either).