Delta

[winnie]

http://forums.mikeholt.com/showthread.php?t=105794

First:
I am wiring a machine in a marble shop.
The machine says 115v 3 phase Y and the control panel has a spot to land 3 hots, one neutral, and one ground.
Three of the motors are 120v.

Normally, when the voltage of a three phase service is quoted, it is the line-line voltage.

120V line-neutral is very, very common, and my _guess_ is that the machine really wants the 208/120 wye supply that iwire mentions.

But because of the way the nameplate says 115v, I would double check to see if the machine is supposed to be connected to a common 208/120 service, or if it really needs something strange.

In particular, check the motors. Are they 120V single phase motors connected line-neutral, or are they connected line-line?

-Jon

 

[Besoeker]

My home is supplied by one voltage system, it happens to be one 120/240 system.

That's kinda my point. It may be one system, but you have two voltages.
In UK, residential voltage is just 230V.

 

[Besoeker]

[From here ECN

OK, so maybe we do have some odd set ups :grin: but at least we drive on the right side of the road.

For what it's worth I don't run into the open delta service in my area, predominately all Wye services.

Thanks for that. I had forgotton about using a centre tap on one winding of a three-phase system. It's just not something that's done here but I understand the concept.

And the driving thing - well yes, you drive on the right-hand side of the road. That doesn't make it the right side. :wink:
The highlight of our drive to work is the "Magic Roundabout".
http://en.wikipedia.org/wiki/Magic_Roundabout_(Hemel_Hempstead)
My wife's from GA and not used to roundabouts at all. You can only imagine how she felt about this one.

 

[iwire]

I saved one customer about $6K by re-using the existing high-leg service and the two fusible mains; a 125a 3ph and a 200a 1ph.

Bad business, you threw away a bunch of money and cut the legs off the other ECs.

JMHO,

 

[LarryFine]

Bad business, you threw away a bunch of money and cut the legs off the other ECs. JMHO,

The POCO would have gotten the $6K, not me. I made more than I would have if I had to replace perfectly usable stuff.

As for "the other EC's," I'm not sure what you mean. I was able to charge a little less and spend a lot less. Was that evil?

 

[charlie]

. . . Nobody would specify an open-Delta service today . . .

We do, even with three primary phases available. Two transformers are less expensive where the customer only has a small three phase load and the rest is single phase. We use them for the stop and robs (convenience stores), lift stations, filling stations, etc. It is not the customer's choice, we normally give him what he requests unless it is extra cash coming out of our pocket. :smile:

 

[LarryFine]

It is not the customer's choice, we normally give him what he requests . . .

Why does that sound like a dichotomy? :smile:

In my case, the architect had specified a 208Y/120 service, but the building had run fine for years on the high-leg 4-wire service before the demo. I kept the existing drop, mast-mounted CT's and meter, trough, and fused switches w/ new fuses.

He worked with me to use the existing above entrance equipment (new panels, of course), which kept the customer from having to pay the POCO $6K for new transformers. I didn't have to replace any of the above, saving cost and labor.

Added: Another benefit: we kept the old 1-ph panel hot during construction. I placed a 3-gang GFCI-receptacle box under the panel. The building was gutted to the framing, even exposing dirt under the floor in some places.

 

[charlie]

Why does that sound like a dichotomy? . .

If the customer is adding enough load to make 208Y/120 needed, we will change it without a problem. If the customer wants 208Y/120 and he only has a 5 HP and a 10HP motor, we are giving him 120/240, 3?, 4w unless 208 is available without building a new bank. Meet the requirements and you get what you want, is that a dichotomy? I think not.

 

[peter d]

We do, even with three primary phases available. Two transformers are less expensive where the customer only has a small three phase load and the rest is single phase. We use them for the stop and robs (convenience stores), lift stations, filling stations, etc. It is not the customer's choice, we normally give him what he requests unless it is extra cash coming out of our pocket. :smile:

One of our local utilities that was swallowed up by "National Grid" used the open delta setup as well, for the same small loads you mentioned. Now that they are part of National Grid they standardized the practice of using 208Y/120 everywhere.

Edited to remove the derogatory name for National Grid. Charlie