two phase or three phase

I am noticing on Kolker's spec sheet:

Now my understanding of two phase is that your have three wires. The middle one is ground, one of the outer ones is

My understand of three phase is four wires. One ground and three other wires of 120V that are 0 degrees 120 degree, and 240 degrees

Am I missing something here? How did Kohler come up with three phase and 240 volts?

Many thanks,

-T

By chance are they using one of the three phases for the neutral and not using a forth wire for the return?

The transformer supplies 120/240 single phase . The load side of the transformer has a "tap" coming from the center of the winding . Loads hooked to the center tap and either side will be 120 , across the whole winding will be 240 V . All the same phase .

It's called split-phase, but it does look and act like two 120V phases 180 deg apart.

Typically it's those 3 plus a ground. Some applications can have a neutral added too, so then it's 5 wires.

Niagara Falls generators were originally two phase. They've been changed out. Some areas of Philadelphia still use two phase. I've seen three phase 240vac for hookups to grain bins. That's because the dryer fans need more power than single phase could supply. There's a 10 hp. limit in my are for single phase.

Forget about the 2 phase and 3 phase stuff. What you and most all homes in the US has is a single phase with a center tap. Three wires plus maybe a ground come into the house. Across 2 of the wires is the 240 volts. From the neuteal wire to either of those two wires is 120 volts.

There are some odd ball places that seem to have 120/208 volts. Seems like the standard for the US is not so standard.

Almost no homes will have 3 phase going into them. That is for larger users of electricity and especially if they have large motors.

People often call what is comming into the house as 2 phase, but that is not true two phase. It is single phase with a center tap.

True 2 phase was never used in most homes of the US. I think there may have been some in the New York area but it is an exception to most of the US.

People may use several voltages when talking. They are all the same such as 110/220, 115/230, 120/240. Over the years the power company has been upping the voltage. My house is often 126/252 as measured by a meter I have traced to the government standard.

I think the 208 comes from 440 3 phase with the transformer wired wye (or is it delta? memory fails me on this one) . 440 between legs but only 208 from any one leg to neutral/ground . Been a lotta years since that knowledge was useful to me ...

I forgot where the 208 comes from. It may be 208 3 phase with 120 volts on the center conductor. At the plant we has about 2 circuits that had

On the 440 volt circuit the Y was used and it is 277 volts from the center of the y to one leg. Mainly used for the lighting circuits where I worked. Had to make sure all 3 breakers for the hot wires were cut off before the circuit was totally dead.

Hi Snag,

This has all been a trip down memory lane for me as I hold a bachelors degree in electrical, electronics, and computer engineering.

If a center tap transformer is using one of the the upper or lower legs as neutral, then your explanation holds.

But if the center tap is used as neutral, the two legs are of equal and opposite polarity (180 deg out of phase with each other).

I use to do this all the time with "push pull" amplifiers.

And if your are really cleaver with the winding, you can have two legs that are 90 degrees out of phase and a third legs that absorbs any standing waves reflected back to the transformer from your load, usually and antenna. I use to do this all the time with Low Noise (radio) Amplifiers (LNA's). Got really good at it too. I use to design radio circuit in my 20's and 30's.

A standard house look to me to use a Center Tap neutral. It is if this guys paper holds true:

This is where my confusion comes in. Why would Kohler be specifying out a three phase generator if you had an electric dryer and stove, but a single phase generator is you had a gas stove and range? Both my dryer and my range are both two phase.

Maybe they are using one of the thee phases as neutral? But that does not make any sense to me.

-T

So they can sell that generator to customers that will use it for split-phase residential like you or customers that will use it for light commercial that needs 3 phase for some equipment.

Try sci.electronics.design

We had a residential area with 3 phase for the air conditioners. I think they got a deal on the units buying in bulk - it happened before I got there so I don't really know.

Anyway, that meant 208 leg to ground. The occupants all complained their dryers took longer to dry, and the stoves longer to heat up.

Wait, I think I said that wrong. I think it is 120 leg to neutral, and 208 leg to leg.

Which brings up a thought. In an average US house, you have 240/120, and you try to divide up the load equally between the hot buses. Theoretically when the loads balance there is no current on the neutral. But you're always adjusting it, turning on lights or appliances, the refrigerator kicking on, etc.

Do they make a load center that can shift loads to keep it balanced?

while most of the US does "center tapping" to bring "two hots and a neutral" (plus safety ground) into houses and small buildings, thus giving you 120VAC when hot <-> neutral and 240VAC hot <-> hot, plenty of building in the NYC area use two legs of a three phase wiring setup.

This is common in apartment buildings and many commercial structures, so that...

apt # 1 will get Leg A and Leg B, plus neutral. apt # 2 will get Leg A and Leg C apt # 3 will get Leg B and Leg C.

Rinse, lather, repeat.

All three "hots" will feed into the three-phase motor used for the elevator, pehaps water pumps, and to the common area, large, central air conditioners.

What this leads to is that... the so-called "240VAC" is actually (the equivalent of) 208VAC, which, as the earlier poster pointed out, dramatically cuts down the actual heat you get in electric dryers and stoves.

(Not as noticable in ovens)

It's worse than you'd think. 208 is bout 85% of 240, so at first glance you might say it's just ("just") a 15 percent reduction in throughput, with only a modest time increase, BUUUUUTTTT

that 15% voltage reduction _also_ means a 15% [a] reduction in amperage, so that actual wattage going through is cut by about 30% (numbers rounded). That adds up pretty quickly. And the horrors of trying to match color renditions ("colour temperature") of incandescent lamps as the voltage changes will give you headaches.

And in regards to motors? supposedly most are designed to handle that range od 208 - 240VAC without hiccuping, but... well, I can tell you from personal experience we had a half dozen modestly large (25,000 or so BTU/hr) window air conditioners quickly die when used at the lower voltage.

This despite specifically asking both the local sales reps and the corporate hq mouthpieces if they'd be ok running at 208.

It is time for you to revisit your text books. True two phase is actually 90 deg out of phase and not 180 deg like you get from a center tapped transformer or the push pull amplifier circuits. Often 4 wires are used for the true 2 phase instead of 3 wires like the split phase (single phase) found in most of the US power grid.

- single phase, not 2-phase, but the addition of a neutral causes a bit of a split personality and a lot of misunderstandings.

There are some , or used to be, appliances that are built for the lower

At work we had some heaters that were rated for about 2 or 3 KW. They looked identical but some were rated for 208 and some for 240. The plant had a few areas that of all things had 208 volts. The 208 units did not last too long at 240 volts. Where they were used it did not make much difference if the 240 volt units were put in the 208 power. They were just in block buildings about 10 feet square that housed some fire protecton valves and pipes.

Many MURBs have 3 phase power - and that is where you generally find

I haven't seen such a thing.

I think the general idea is that even if one home is unbalanced in one direction, the next home might be unbalanced in the other direction, thus smoothing things out. Across an entire neighborhood, perhaps the difference becomes slight.