# Wiring three phase:  Oxtools/BarZ approach



## rabler (Apr 12, 2022)

Anyone seen Tom Lipton's latest Epic Egress youtube video, and the approach on wiring in the three phase?  Basically he wired the whole shop off a three phase panel even though it's currently run off a 30HP RPC.  So two legs are driven from the utility transformer and the third leg in the panel is from the RPC.  Makes sense to me IF he does go with three phase power from the utility.  If he keeps the RPC, I think I prefer having the 3 phase self contained from the single phase.   But, I hadn't even thought of that approach ...


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## FOMOGO (Apr 12, 2022)

I watched it this morning, and found the 3phase panel setup interesting. Too late for me, as my panel is in and a have a 3phase breaker panel for my converter waiting for me to get to it. If I was just starting it would be something to consider. Not sure if that meets code or not, but don't see why it wouldn't.


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## C-Bag (Apr 12, 2022)

I also watched that partially because watch everything Tom puts out, but also because shop power is something I’ve been contemplating. The one thing I was surprised by was that his well pump was not 3ph. Not that I’m any kind of expert but the two we’ll pumps I was exposed to were 3ph. That’s how my FIL got 3ph into his shop. Tom mentioned that there was a 3ph pole tantalizingly close, but who knows how much PG&E would charge to run him 3ph.


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## woodchucker (Apr 12, 2022)

I didn't see anything surprising, seemed pretty basic. Having watched Stan help other guys he is very good about this. His business is doing industrial buildings, setting up ---- you name it---- so he's quite savvy on wiring. I guess I didn't know enough to realize it was unusual.


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## rabler (Apr 12, 2022)

woodchucker said:


> . I guess I didn't know enough to realize it was unusual.


More of a "wish I'd though of that" than saying it is unusual.  And then going on to figure I'd probably keep my current config even if I'd thought of it.  I only have 2 or 3 three phase machines, and lean toward VFDs for the smaller stuff so don't expect that to grow radically even if I do get more.  But it is rather elegant.


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## C-Bag (Apr 12, 2022)

I thought it was interesting that the only job of that big 30hp phase converter was to generate the third leg. But don’t know enough beyond that to just wonder…..


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## woodchucker (Apr 12, 2022)

well, that's all a rotary phase converter does, is generate the 3rd leg.
That's all mine does.  I have 2 legs, and by spinning that motor, I get a 3rd leg.
I don't have a 3phase breaker box, nor do I need one. I only have one machine currently.
But if I had a number of pieces of equip and knew I'd buy and sell equip as needed, I think having the panel makes good sense.


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## rabler (Apr 12, 2022)

C-Bag said:


> I thought it was interesting that the only job of that big 30hp phase converter was to generate the third leg. But don’t know enough beyond that to just wonder…..


That's all an RPC really does.  The other two legs are just passed through from the single phase.

I guess in the end it is just a question of how many single phase (120/240) vs 3 phase breakers you use, since you don't want to pull single phase power off the generated leg with an RPC, but no reason not to (in fact it's better for load balancing) if you have utility line 3 phase.


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## C-Bag (Apr 12, 2022)

woodchucker said:


> well, that's all a rotary phase converter does, is generate the 3rd leg.


Well I just learned something I didn’t know. I just assumed it was like a vfd and generated all three, doh!


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## rabler (Apr 12, 2022)

Bad thing in that configuration would be that you could put a single phase breaker on your generated leg (i.e., in the wrong slot on the panel), and it would not pull 120V but would give you around sqrt(3) * 120V = 208V when the RPC was running.

I guess this is classic high leg delta, so shouldn't be a problem for an experienced industrial electrician, but a DIY Joe shop owner might run into trouble with this.  Maybe @Bi11Hudson will weigh in with some thoughts.


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## extropic (Apr 12, 2022)

I think the real bonus for Tom is that, if he ever gets 3Ph from PG&E, his panels are all set up. Pull new 200A conductors from the disconnect (behind the meter) to the load center (shop) and Bob's your Uncle.

I also watched three Bar Z's tutorials on conduit bending (as recommended by Tom). What a joy.
I've bent a little conduit and watching a Pro explain a few things was a lot of fun.


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## rabler (Apr 12, 2022)

extropic said:


> I think the real bonus for Tom is that, if he ever gets 3Ph from PG&E, his panels are all set up. Pull new 200A conductors from the disconnect (behind the meter) to the load center (shop) and Bob's your Uncle.
> 
> I also watched three Bar Z's tutorials on conduit bending (as recommended by Tom). What a joy.
> I've bent a little conduit and watching a Pro explain a few things was a lot of fun.


I’d also guess Tom has been around enough industrial settings to know enough not to het in trouble.

watching those conduit videos is on my list, if I can remember his channel name, as I intend to use metal conduit for my few 3 phase drops.


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## Dabbler (Apr 12, 2022)

To answer the original question:  it depends.  Every wiring style has its trade-offs.  I wired my shop single phase, and used VFDs for years.  Now that I have a phase converter, I'm not about to rewire everything.  I currently run a 3PH extension cord to my 3PH machines.

I'll be putting a small pony 3PH panel suitable for the smallest number of breakers I can find. The 3PH plugs will be different from the rest - probably I'll choose 40A Hubble in Orange, to differentiate from  my plethora of other plug styles


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## Karl_T (Apr 12, 2022)

Did this one for the kid back in 2014.








						25hp 3pahse conveter with load center
					

25hp 3phase converter with load center  *Reposted from another forum - summer 2014 project*   My son is building a new shop. He's one hell of a machinist and CNC programmer, but challenged with electricity. So, I'm building a deluxe converter setup he won't outgrow.  For an overview, this...




					www.hobby-machinist.com
				




A load center really makes it easy to add more equipment as needed.

Also did this one:








						Ultimate 3 phase converter
					

I will soon be helping my son build what I'll call the ultimate 3 phase converter.  he has just built the ultimate shop for his life - a 30' x 40' super insulated building with in floor heat.   This will be the fifth rotary converter I've built over the last 25 years.  There is a five year old...




					www.hobby-machinist.com


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## rabler (Apr 12, 2022)

@Karl_T Yep, that’s my plan when I get to the three phase part of my shop build, extend my RPC from a simple 20HP idler to a dual 10+20 idler configured to run as 10, 20, or 30 HP worth of idler. I’m also going to interface the lights so that if they get turned off the RPC cuts out a minute or so later as long as there is no load on the generated leg.  With an isolated motor I will otherwise forget to cut it and the compressor off.


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## rabler (Apr 12, 2022)

Dabbler said:


> To answer the original question:  it depends.  Every wiring style has its trade-offs.  I wired my shop single phase, and used VFDs for years.  Now that I have a phase converter, I'm not about to rewire everything.  I currently run a 3PH extension cord to my 3PH machines.
> 
> I'll be putting a small pony 3PH panel suitable for the smallest number of breakers I can find. The 3PH plugs will be different from the rest - probably I'll choose 40A Hubble in Orange, to differentiate from  my plethora of other plug styles


Siemens makes a panel which I am using that holds four three phase breakers.


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## ahazi (Apr 12, 2022)

rabler said:


> That's all an RPC really does.  The other two legs are just passed through from the single phase.
> 
> I guess in the end it is just a question of how many single phase (120/240) vs 3 phase breakers you use, since you don't want to pull single phase power off the generated leg with an RPC, but no reason not to (in fact it's better for load balancing) if you have utility line 3 phase.


I don't get that...
3 phase feeds are 120 degrees apart. If you just add the 3rd leg, existing 2 phase are 180 degrees apart.
As far as I know, 3 phase motors rely on the 120 degree phase difference between the feeds for starting the motors and getting good torque and efficiency. What am I missing?


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## rabler (Apr 12, 2022)

ahazi said:


> I don't get that...
> 3 phase feeds are 120 degrees apart. If you just add the 3rd leg, existing 2 phase are 180 degrees apart.
> As far as I know, 3 phase motors rely on the 120 degree phase difference between the feeds for starting the motors and getting good torque and efficiency. What am I missing?


What you are considering is where the neutral is referenced to.   In standard three phase, the neutral is often considered to be the center of the triangle.  So 120 degrees between legs relative to neutral.  In high leg delta 3 phase (google it for pictures), the neutral is the center of one side of the triangle.  So two legs are 180 and one is 90 from neutral, but it is still an equal lateral triangle, 240 volts between any two legs.  3 phase motors don’t use neutral, so they don’t care what neutral is referenced to.  RPCs produce 3 leg delta (correction, high leg delta) which is why you measure line to line voltage but get funky results for line to neutral.

Three leg delta is also fairly common in industrial use.  It delivers the classic 3 phase, plus 240v and 120v single phase.  Otherwise you get 3 phase with 208V leg to leg and 120V leg to center of the triangle neutral.  A 240V 3 phase center to neutral would give something odd like 138V.  At least I think that’s right, I’m doing geometry in my head so my math is not guaranteed.


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## extropic (Apr 12, 2022)

@rabler 

You remember that I've already admitted to being electrically (and electronically) challenged, so excuse me.

IIRC, a very long time ago, I learned that single phase service is actually 120° (not 180°). Is that correct?

It made sense (at the time) related to pulling 1Ph off of 3Ph service and also generating 3Ph using an RPC.


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## rabler (Apr 12, 2022)

extropic said:


> @rabler
> 
> You remember that I've already admitted to being electrically (and electronically) challenged, so excuse me.
> 
> ...


It’s a vector problem.  You really can’t define an angle without two phases, two different sine waves. You measure a voltage between 2 points.
voltage=Vrms*sqrt(2)*cos(angle+2*pi*f*t), where f = 60Hz for US power.  Angle is the the angle at t=0, but what defines t=0? (who cares? no one) So unless you’re dealing with more than single phase, angle is arbitrary.

In a 3 phase center neutral configuration, you have angles of 0, 120, and 240 from neutral to the three legs.  But running three phases plus a neutral is 4 wires on the power line.  The power company doesn’t run a high voltage neutral.  Less wire is easier.  They use transformers between any two legs to pull off single phase.   Those two legs are at 120 degrees relative to the third leg, but without the third leg that angle becames meaningless.  (They actually try to rotate which two legs to balance the loads).  This produces one sine wave (cos wave) but since t=0 is arbitrary it doesnt really have an angle.  Your 3phase motor will run fine off this config.

Since the transformer isolates the low voltage side, Neutral is determined by where the ground rod is attached.  In a pure three phase only system, you could ground one of the legs.  (IIRC this is called a corner ground system).  The vector triangle is the same shape, it just shifts where relative to the origin it is placed.  As long as your triangle maintains that shape, your three phase motor runs fine.  Rotation and translation of that triangle don’t impact the motor.

The big fallacy, common even among EE’s, is there is some magical definition of a zero voltage point called ground.  That is typically choosen as the local electrical potential of the earth.  But an experiment on my old campus in the early days of networking showed a difference of up to 90V between two such rods less than a mile apart, and don’t ask what it is if a lightning strike occurs nearby. This has some nasty implications for attempting to send low voltage Ethernet signals between remote buildings.


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## extropic (Apr 13, 2022)

@rabler 

Reading your reply, I realize I didn't ask the question well enough.

In your reply, when you say "You really can’t define an angle without two phases", does that mean the two hot (120V) legs of 240V single phase service are not "two phases"?


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## Dabbler (Apr 13, 2022)

In a *delta *3phase system each of the two terminals make a single phase sine wave 240V RMS  there are 3 ways to connect to a 3 phase source, and each of those sources are 120 degrees apart.  In a *Y* 3 phase system each of the sources measure 208 volts RMS. 

There is no other 'geometry' here.

There is no practical use for using two of the 3 phases BTW.  I cringe when people refer to 240 V as "two Phase" based on the number of wires. 
Please, just don't.


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## ahazi (Apr 13, 2022)

rabler said:


> What you are considering is where the neutral is referenced to.   In standard three phase, the neutral is often considered to be the center of the triangle.  So 120 degrees between legs relative to neutral.  In high leg delta 3 phase (google it for pictures), the neutral is the center of one side of the triangle.  So two legs are 180 and one is 90 from neutral, but it is still an equal lateral triangle, 240 volts between any two legs.  3 phase motors don’t use neutral, so they don’t care what neutral is referenced to.  RPCs produce 3 leg delta, which is why you measure line to line voltage but get funky results for line to neutral.
> 
> Three leg delta is also fairly common in industrial use.  It delivers the classic 3 phase, plus 240v and 120v single phase.  Otherwise you get 3 phase with 208V leg to leg and 120V leg to center of the triangle neutral.  A 240V 3 phase center to neutral would give something odd like 138V.  At least I think that’s right, I’m doing geometry in my head so my math is not guaranteed.


Thanks! You are right. I ignored the fact that the *neutral is not used* and it is only 2 floating legs so it is easy to create a 3rd leg that has the proper phase relationship. 

I grew up and did early tinkering many years ago with 240/380 volt systems. Each house received 3 phase power so the notion of rotary phase converter was non existent. The phases always aligned properly in regard to neutral in Y configuration. Power plugs were almost always 5 pin with 3 phases, neutral and ground. Ground was never tied up to neutral as this seems to be a US standard of tying the power transformer CT at the pole to ground.


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## rabler (Apr 13, 2022)

extropic said:


> @rabler
> 
> Reading your reply, I realize I didn't ask the question well enough.
> 
> In your reply, when you say "You really can’t define an angle without two phases", does that mean the two hot (120V) legs of 240V single phase service are not "two phases"?


The two legs of 120V are indeed 180 degrees out of phase.  In my mind that is indeed two phases, described mathematically be two different angles, or two different vectors.  But, they are generated by a center tapped transformer.  On the high voltage side there is only one voltage, generating both 240 and/or splitting that into two sets of 120v.  So power guys think of it as single phase.  My background is more signal related so I would say its one phase of 240 or two phases of 120.  This gets to be almost a religious argument, depending on background.  Convention in nomenclature is to count phases on the powerline side.


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## rabler (Apr 13, 2022)

Dabbler said:


> In a *delta *3phase system each of the two terminals make a single phase sine wave 240V RMS  there are 3 ways to connect to a 3 phase source, and each of those sources are 120 degrees apart.  In a *Y* 3 phase system each of the sources measure 208 volts RMS.
> 
> *There is no other 'geometry' here.*


@Dabbler Not completely true.  See the wikipedia article on high leg delta for another example.  Admittedly this is a variation of the delta configuration, but it is an important difference when a site uses both single and three phase.

  Voltage is just a function of the number of windings on the transformer.  You can generate either one of those delta or y configs from the same high voltage lines, or 440V, or …
Further, a transformer in itself doesn’t have a ground reference.  It floats unless a ground is established.  Where that ground is established is makes a difference, and that can be different at two different customers on the same high voltage three phase utility line, as long as those two customers are on different transformers.

Delta and Y are really terms applicable to how three phase power is used in a motor or three phase transformer windings.  Since a power utility has to supply power to more than three phase motors, it’s oversimplifying to think those are the only configurations.


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## ahazi (Apr 13, 2022)

Interesting discussion. 

Reminds me of the methods to generate higher voltage with autotransformer (110 volt to 220 volt for example). The transformer needs to be sized only to half the load, the other half is directly from the source.

This explains how the rotary phase converter motors are *much smaller* than a similar sized 3 phase motor as it only needs to generate 1 phase that is 1/3 of the load.


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## StevSmar (Apr 13, 2022)

I wondered what would happen if you forgot to turn the rotary phase converter on. Wouldn’t you be single phasing your three phase motor (and it would draw a lot of current)?

Perhaps if you connected one leg of the machines controls to the derived leg, then if that phase wasn’t present then either there would be no power available to the controls or the fuse of the controls would blow? (I don’t know what voltage the derived leg sits at when it’s not connected to the phase converter. It seems likely it will just float and can’t provide power?)

(Also, if the derived “neutral point” is not near zero, wouldn’t this also mean the insulation of the devices to ground needs to be higher too? And therefore the machines insulation voltage would also need to be confirmed?)

(I haven’t thought about this much since seeing the video(s (Oxtools and Keith Fenner), except for thinking I’d be very likely to forget to turn the rotary phase converter on eventually…)


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## Dabbler (Apr 13, 2022)

rabler said:


> oversimplifying to think those are the only configurations.



Agreed.  

In the specific answer to the original question as to the notion that single phase is not 'in sync'.  I am attempting to explain that each of the phases is a complete supply in itself.  Many people are lured by the phase diagrams into false assumptions.  Using 120v/240V systems here in N America further complicates people's understanding of what is a very simple system. 

I could have written pages about the configurations I have seen in industrial settings.  And then there's phase matching and distribution issues that are actually complex.  We could talk for days!

I appreciate your clarification!

---

BTW  the first Rotophase I installed:  it  was to repair the installation that was done by a "Master Electrician"  who was supposed to be trained in both industrial and residential installations.  He had  mis-wired the capacitors in the converter (in those days, late 70s, the internals were not completely wired - they were adapatable to the installation re delta versus wye motors)  He had ruined 3 of the 6 capacitors when testing.  They literally burst. 

I came in because it was I who recommended the electrician.  Here's me early 20s - no electrician's ticket, no training, never wired 3 phase before...  I looked at the manual,  wired up the new capacitors ($700 worth), checked everything, and it worked for over 40 years.  When the inspector came in, we told him about the incident, what I did to mitigate it, and he passed the installation.  Here in Canada, your insurance is dependent on that inspection.  This was in an industrial bay running a bunch of 3 phase equipment.

The business was sold and closed down 3 years ago.  I'm using that same Rotophase today.


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## rabler (Apr 13, 2022)

StevSmar said:


> I wondered what would happen if you forgot to turn the rotary phase converter on. Wouldn’t you be single phasing your three phase motor (and it would draw a lot of current)?
> 
> Perhaps if you connected one leg of the machines controls to the derived leg, then if that phase wasn’t present then either there would be no power available to the controls or the fuse of the controls would blow? (I don’t know what voltage the derived leg sits at when it’s not connected to the phase converter. It seems likely it will just float and can’t provide power?)
> 
> ...


Yes, that should prevent you from being able to start the motors on many machines.  But connecting controls to the derived leg is generally bad for two reasons:  the derived leg is less well regulated and usually the controls are what are going to be more sensitive to the voltage fluctuation.   Also, RPC's generally start better with no load on the generated leg, and the control circuits are the most likely to put a load on that leg with the end machine not fully on.  I've retrofitted my three phase lathe with a bright indicator light across the controls leg to show that it is on so I know to throw it's internal disconnect switch, although my RPC is set up so that when it is off, all three legs are disconnected.

If your RPC isn't running, your three phase motors generally won't start at all, so you'd know something was wrong.  Hopefully you'd turn the machine off relatively quickly.


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## Dabbler (Apr 13, 2022)

rabler said:


> that should prevent you from being able to start the motors on many machines.



In my installations, there is a 3 phase contactor that does not engage until the phase converter is up to speed, - about 2 seconds. That way, all the legs are dead until all legs are available.  I think of this as a safety issue.

In one shop with a home made converter. the guy turned on his lathe.  All you could hear was a loud 60 cycle buzz.  He said "oops" turned off his lathe , and then turned on his phase converter... and his lathe ran fine.


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## Winegrower (Apr 13, 2022)

rabler said:


> But connecting controls to the derived leg is generally bad for two reasons: the derived leg is less well regulated and usually the controls are what are going to be more sensitive to the voltage fluctuation.


This seems to me to be a not widely understood point.   In my machines that have lights and other single phase equipment these are wired using the two pass through legs from either a rotary or static converter.   It can be a bit of a puzzle to figure out on the machine side which wires to connect to what supply wires, especially without a schematic.   Fortunately motors don’t care, other than for direction.


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## StevSmar (Apr 13, 2022)

Dabbler said:


> In my installations, there is a 3 phase contactor that does not engage until the phase converter is up to speed, - about 2 seconds. That way, all the legs are dead until all legs are available.  I think of this as a safety issue.
> 
> In one shop with a home made converter. the guy turned on his lathe.  All you could hear was a loud 60 cycle buzz.  He said "oops" turned off his lathe , and then turned on his phase converter... and his lathe ran fine.


That’s interesting! Good to know his lathe ran fine!

(I’ve heard of installations of 3-phase systems where the machines overcurrent protection or starter didn’t detect for phase failure of the facilities electrical service and they ended up burning out motors. Which is what made me wonder what would happen if the phase converter wasn’t on)


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## rabler (Apr 13, 2022)

Dabbler said:


> In my installations, there is a 3 phase contactor that does not engage until the phase converter is up to speed, - about 2 seconds. That way, all the legs are dead until all legs are available.  I think of this as a safety issue.
> 
> In one shop with a home made converter. the guy turned on his lathe.  All you could hear was a loud 60 cycle buzz.  He said "oops" turned off his lathe , and then turned on his phase converter... and his lathe ran fine.


I've seen commercial RPCs set up both ways, either turning the RPC off kills all output, or turning off the RPC turns off only the generated leg.  I hardily agree with the idea that all power off is preferable.


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## Larry42 (Apr 13, 2022)

Where I live they no longer will provide 240V single phase, only 208V. As I understand, it is about balancing the system. My old shop had 240 3 phase but since the 120V was provided off only 2 legs the 3rd leg was referred to as a wild one since it couldn't be used for 120V.
I have a German machine that uses a timer to switch between Y & Delta windings on the motors. As I understand the reason, it reduces the inrush current load on the utility. There must be some way of changing the resistance to change the amperage. Are the windings sort of split in two for one configuration and not the other? What happens if the timer doesn't switch winding configuration?


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## rabler (Apr 13, 2022)

Larry42 said:


> Where I live they no longer will provide 240V single phase, only 208V. As I understand, it is about balancing the system. My old shop had 240 3 phase but since the 120V was provided off only 2 legs the 3rd leg was referred to as a wild one since it couldn't be used for 120V.
> I have a German machine that uses a timer to switch between Y & Delta windings on the motors. As I understand the reason, it reduces the inrush current load on the utility. There must be some way of changing the resistance to change the amperage. Are the windings sort of split in two for one configuration and not the other? What happens if the timer doesn't switch winding configuration?


My limited understanding is that power balancing is indeed a real ongoing challenge for utilities.  It is made worse in the US in that residential distribution pulls a single phase for most neighborhood.

I don’t have hands on with y-delta motors.  But they don’t change the resistance, rather if you have three wires in three phase, those wires have a phase to phase voltage (delta configuration) that sqrt(3) times the voltage you get from hooking up those same three wires in a y configuration.  Thus, the Y config is lower voltage.  By separating the motor windings completely (6 wires coming out of the motor), you can hook the motor up in Y config to start.  Lower voltage-> lower amperage.  This lowers the startup inrush current.  Once the motor is spinning then it is switch over to delta, increasing the voltage and thus increasing the running amperage, but running amps is much less than startup, while still providing the higher torque/power that comes with higher voltage.  Generally works better for motors that do not start under heavy load.  If the motor fails to switch over, then it will run with much less HP, and could overheat when loaded, damaging the motor.


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## Larry42 (Apr 14, 2022)

rabler said:


> If the motor fails to switch over, then it will run with much less HP


Thanks, I suspected that.


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