Motor 120V 3-Phase

[j j]

really....

what do you get then, oh great HA HA?

3 wires come in the house from the utility, what are they?

[j j]

you get 3 phase power in a residential unit?

[j j]

do you get all 3 voltages at the same time, and out of phase?

[Tom Horne]

I can take a buck boost transformer that has four taps on the secondary and ground one of those taps. I will have three different voltages relative to the grounded tap. Is it your position that I know have a three phase transformer?

Why does a 240 volt motor that is connected to a center tapped 120/240 volt seccondary need a capacitor to make it turn?

-- Tom H

[HA HA Budys Here]

I'll tell ya. The 2 "phases" as you call them are not phases at all. Each is derived from the same primary phase. There is however, relative to their reference to neutral,

240v difference between them.

secondary primary windings windings

(1)----------) ( ) ( (n)----------) ( (*) ) ( (2)----------)

You know between either 1 or 2 and N you get 120v, and between 1 & 2 you get

240. Now add a tap at the (*) and say that's 60v to (n) - it would also be 60v from * to (2) and 180v between * and (1).

Now, would this be a 3-phase transformer? No, and that's why these kinds of services are called single phase 120/240.

[volts500]

Tom, I've been doing electrical work in "heavy industrial to home environments" for 27 years, and I've never seen a 120 volt 3 phase motor either, nor a 3 phase 120 volt (line-to-line) system..............but if you look at NEC (2002) Table 430.150 it does indeed show FLC's for 115 volt 3 phase motors 2 HP and under.........so, evidently, they must exist somewhere for some special purpose. Also see the commentary at the beginning of Article 647 in the NEC Handbook........evidently the motion picture and tv production industry (NEC Article 530) has been using a 60/120 volt 6 phase wye connected system for some time, for noise reduction when they set up to shoot in "dirty" electrical environments. It's being referenced as "balanced power" or "technical power." Seems the 2002 NEC (new) Article 647 is now permitting these systems for just about any sentitive electronic equipment requiring isolation.........computers, medical equipment, etc.

[Wade Lippman]

Follow the link. Can't be much clear than that.

[CBHvac]

One of my old customers there sure as hell did. We went to replace his old AC unit, and be damned if he didnt have 3 phase hitting the board.... Turns out, that everyone on his block was like that...and it was residential.

[Dean Hoffman]

Would it be practical for the original poster to use a static phase converter for this motor? Maybe he'd be better off to just buy a regular single phase 1 hp motor money wise.

Dean

[j j]

well, then I guess every network is different. Where I live, I'm pretty sure we don't get 3 phases (I have no idea how it is in a building, I live on a street with houses only). On my street there's no transformer, the phases get split somewhere else.

[j j]

again, are these voltages out of phase? if not, no you don't have different phases, but if the voltages are not in phase, then they're different phases. the 2 120V lines most people get in their residential units are 180 degres out of phase, which is why together they can make 240V.

because them otor is being fed a single 240V phase and it needs at least 2 phases to run, the capacitor gives a 90 degree phase shift.

[volts500]

No, Tony, only an electronics "wizahd" like you would confuse BPL with "clean" 120 volt power. Wouldn't surprise me if you told the OP to wire the motor up with some Cat5.

[volts500]

I think the OP has a $5 boat anchor. Have you ever seen a converter with a

120 volt output?

[Tom Horne]

Make up my mind! Either the two conductors that supply the 240 are a single phase or they are two phases. There is no difference between my buck boost transformer and the utilities center tapped single winding secondary service transformer except for the number of taps. They both have a primary that is connected to one grounded conductor (the Multi Grounded Neutral [MGN] in the case of the utility transformer) and a single conductor that has a voltage relative to the grounded conductor. They both have points on the single secondary winding that are tapped so that different voltages can be supplied from the same transformer. If the utility transformer is two phase why isn't my multi voltage secondary with three voltages relative to the grounded tap three phase?

-- Tom

[j j]

if you take a 3-phase 120V/phase Wye connection, line to line you get 208V

Are the 3 phases separate or the same phase? If you take the line to line voltage, (using one phase as the neutral) do you get another phase of 208V or is it the same phase?

I dunno, by the basic definition of "phase", since the 2 120V lines in the house are 180 degrees out of phase, they are different phases. If they're not in phase, they can't be the same phase...

[TURTLE]

This is turtle.

You have them somewhere but maybe you have transformer bank / Mini-Substation on the ground some where to feed the hold area.

TURTLE

[Dean Hoffman]

TH:

JJ:

TH:

JJ:

JJ, look at it this way. Your second statement is true. I'm not sure about the amount of degree shift. That means the first one can't be since the 240 volt motor would run fine without a capacitor off residential power. The residential power would supply the phase shift to start the motor without the capacitor. Power companies supply either single phase or three phase in my area. This is in a rural area so the wires and transformers are up on power poles. Three phase has 3 wires plus ground. Single phase has one wire plus ground. The supply to the farm yards is generally single phase 240/120. This is a really crude diagram of a transformer for the single phase 240/120 power.

The top line is the utility's primary high voltage connection.

7200VAC??------------------------------------------- Ground. 120----G----120

The bottom line is the consumer's supply secondary winding. Three wires. Two "hots" and the "neutral". This is a single winding but it has a tap in the middle to provide the 120 voltage line to neutral. There would be only 240 single phase without the center tap. The secondary would be something like this:

240----------G

Two wires, single phase just like the power company's supply voltage.

I did not include the equipment grounding conductor in either of the secondaries.

The power company's supply voltage to the transformer is single phase so the 120/240 to the consumer has to be single phase. There is nothing in the transformer to create a time/degree shift.

Dean

[klm]

My apologies for not posting the full specifications on the plate. They didn't make sense to me then or now. Here goes.

MARATHON ELECTRIC Wausau, Wisconsin 54401 Cat No. K049 Model 6V556T17D2130D P FR 56 PH-3 Type TS

(Left Hand Column) ( RH Column) FLA 1.4 Hz 60 SF 1.15 HP 1 SFA 1.6 RPM 1725 CODE L VOLT 575

Single Voltage L1 L2 L3 T1 T2 T3 (wiring diagram)

FR 56 AMB -40 deg INS-B3 DUTY- Cont. DES B

Looks like I goofed on the voltage (575V) but does such a voltage exist in a 3 phase industrial power source?

The motor has its own attached control box with an ordinary toggle switch hooked with three conductor 16 ga rubber insulated cord, but no power plug connector. It doesn't look right for a 575V system but there it is.

I have already wired an ordinary three prong household plug to the cord but I have not stuck that into any outlet yet to test it. That

575V spec gave me reason to ask first. That was sometime ago until I thought about asking this newsgroup.

A new 1 hp motor costs >$200. $5 for one at a garage sale is a safe bet and if it doesn't work its no loss. And darn, there is not a scratch on it from power on usage so its practically new.

[j j]

actually when I was asked that question, I thought about why a motor wouldn't work with the 2 phases in the house: since the phases are exactly

180 degrees out of phase, the resulting magnetic field in the motor just pulsates, it doesn't rotate, and it's not enough to make the motor turn (at least in an induction motor). a single phase induction motor will need a capacitor to start because the capacitor gives it a 90 degreep hase shift, and the resulting magnetic field will rotate.

but aren't the two hot wires out of phase by 180 degrees? (when one is at positive peak, the other is at negative peak)

[HA HA Budys Here]

You have to change the way you define "phase" for yourself.

A phase, or multiple phases, are segments of a circle.

Multiple voltages, or "legs" derived from a single source, (only 1 phase segment,) are multiple "taps" or "legs," not each an individual phase.

This is why you'll see most 3-phase equpiment labled A-B-C or Phase A - Phase B

- phase C , and most 240v volt equipment, especially residential, labled "L1 & L2" meaning, leg (or line) 1 and leg 2.