# I learned I have 3 phase "high leg" at my new location, and need help using it



## nickmckinney

I just moved into a new building and didn't even realize I have the only 3 phase supply in the warehouse group. I picked up a 3 phase 220/440 machine with a 5HP motor I need to run. A couple buddies looked at my panel and I have 120V on each outer leg and 240V on the center and there is orange tape. I was told its a high leg configuration and that went right over my head. Anyway we are trying to figure out the best way to use the 3 phase machine right up to it. Originally I was going to get a phase converter but now..........


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## Tony Wells

3 phase machines with low voltage controls require that you identify the high leg and make sure it is not feeding the control transformer. Connect either of the low legs to the transformer, and note the tap. Some are tapped for 208, 277, 120, etc.. The other two can be swapped to make your machine rotation is correct.


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## rdhem2

Gentlemen:
It always seems I am the purveyor of contrary news.  Three phase with a wild leg indicates a 240/120v delta connected at the source.  This is a typical, common light industrial supply from the power company.  In other words not enough power demand to warrant a 480/277 wye service.  With the 480v connection it requires the customer to purchase and install his own transformers to obtain power for 120v devices.  The 240/120v delta service provides three phase power at a higher voltage, slightly less amperage demand.  Phase A and phase C providing 120v power when read to neutral.  The B phase is read all over from 190v to 240v to neutral.  We were taught in school by actual calculation with everything perfect by spec and book that the calculated value should be 196v to ground or neutral.  This is because of where the neutral is tapped in the transformer.  You are actually getting power through 1 and 1/2 sets of windings, in relation to the B phase. 

Now the contrary news.  Even though the voltage is high on B phase in relation to phase A and C.  It is still 240v phase to phase no matter how you read it.  Yes the B phase is high.  Yes the B phase will fry anything connected to B phase and neutral.  Hence the reason for the orange tape that is is required at the service panel and is supposed to be used to identify the B phase throughout the system.  But any 240v item does not know or care what phase combination it is supplied by.  A-B, A-C, or B-C, it just does not matter because they all have 240v potential between them.  Single phase or three phase.  Try it out.

Your 3 phase service panel is basically one third useless when needed for 120v loads.  240v single and three phase may be originated from any place in the panel.  120v loads stay away from that darn B, center phase or you will let the smoke out.!

What I have done in the past is to set a single phase sub panel fed from phase A and C, next to the main 3 phase service panel then supply all 120v circuits out of the sub panel.  Keeps confusion down, and it always seems like you run out of space for single pole breakers.


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## John Hasler

rdhem2 said:


> Gentlemen:
> It always seems I am the purveyor of contrary news.  Three phase with a wild leg indicates a 240/120v delta connected at the source.  This is a typical, common light industrial supply from the power company.  In other words not enough power demand to warrant a 480/277 wye service.  With the 480v connection it requires the customer to purchase and install his own transformers to obtain power for 120v devices.  The 240/120v delta service provides three phase power at a higher voltage, slightly less amperage demand.  Phase A and phase C providing 120v power when read to neutral.  The B phase is read all over from 190v to 240v to neutral.  We were taught in school by actual calculation with everything perfect by spec and book that the calculated value should be 196v to ground or neutral.  This is because of where the neutral is tapped in the transformer.  You are actually getting power through 1 and 1/2 sets of windings, in relation to the B phase.
> 
> Now the contrary news.  Even though the voltage is high on B phase in relation to phase A and C.  It is still 240v phase to phase no matter how you read it.  Yes the B phase is high.  Yes the B phase will fry anything connected to B phase and neutral.  Hence the reason for the orange tape that is is required at the service panel and is supposed to be used to identify the B phase throughout the system.  But any 240v item does not know or care what phase combination it is supplied by.  A-B, A-C, or B-C, it just does not matter because they all have 240v potential between them.  Single phase or three phase.  Try it out.



Note that the "neutral" referred to above is not the three-phase neutral but the grounded conductor, which is a center tap on the transformer winding between A and C.



> Your 3 phase service panel is basically one third useless when needed for 120v loads.  240v single and three phase may be originated from any place in the panel.  120v loads stay away from that darn B, center phase or you will let the smoke out.!
> 
> What I have done in the past is to set a single phase sub panel fed from phase A and C, next to the main 3 phase service panel then supply all 120v circuits out of the sub panel.  Keeps confusion down, and it always seems like you run out of space for single pole breakers.



Good idea.  Also simplies changes down the road.  I'd supply all single-phase loads from that panel if possible, not just 120 ones.

Let's hope nobody here ever has to deal with corner-grounded delta...


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## DMS

Many motors can be wired to run off of either a "Wye" or "Delta" 3 phase configuration. If you look on the side of your motor there are often wiring instructions (sometimes they are inside the wiring box). Basically a "high leg" is a "Delta" service (which would normally have 3 legs), but they center tapped one of the transformers to give you 120V for "normal" usage. This center tap is normally marked as the neutral, but you can't use it as a neutral in a 3 phase system. If your machines can be configured to run from a delta service, then just wire them up like the neutral is not there.  

For what it's worth, I have only ever seen or heard of a few people with this type of service, and it always ends up with somebody scratching their heads going "huh?", so don't feel bad


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## itsme_Bernie

Tony Wells said:


> 3 phase machines with low voltage controls require that you identify the high leg and make sure it is not feeding the control transformer. Connect either of the low legs to the transformer, and note the tap. Some are tapped for 208, 277, 120, etc.. The other two can be swapped to make your machine rotation is correct.



Wow,  never knew about a "high leg".  I don't have to worry about it in y situation, but interesting to know that in some situations you have to think about which legs you swap.

Thanks Tony! 


Bernie


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## Dave Smith

Russ and John--what you describe makes sense to me---so if I am understanding you correctly--if you have a three phase motor that can be wired 480 or 220--then the lower voltage connection would be using all three legs --without needing a transformer and without caring that  the third leg is actually higher voltage?----and to change rotation --any legs can be switched even though one is higher? --I understand that some 3 phase motors are high voltage only and need 277v on all three legs.---thanks both for you clearing this up ----Dave


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## John Hasler

DMS said:


> Many motors can be wired to run off of either a "Wye" or "Delta" 3 phase configuration. If you look on the side of your motor there are often wiring instructions (sometimes they are inside the wiring box). Basically a "high leg" is a "Delta" service (which would normally have 3 legs), but they center tapped one of the transformers to give you 120V for "normal" usage. This center tap is normally marked as the neutral, but you can't use it as a neutral in a 3 phase system. If your machines can be configured to run from a delta service, then just wire them up like the neutral is not there.



As long as the motor neutral is not brought out and intended to be connected to the supply neutral (I've never seen such a motor) you can connect a wye-connected motor to a delta supply and vice-versa if the line to line voltage is correct.  

Rewiring a motor from wye to delta (or vice versa) changes the line to line voltage it requires but the motor does not care how the source is wired: just what voltage it supplies.


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## jim18655

Several things here need clarification. If the machine has a 240 volt control transformer then it will make no difference where the high leg is connected. If the machine has a 4 wire cord - 3 phases, neutral, and ground then it will make a difference in the connections because they are getting 120v control power, or lights from one of the phases to neutral, assuming it needs 120v. It could have 240v controls. You must make sure the control circuit isn't connected to the "high leg." As for delta or wye connected motors that depends on the internal connections in the motor. All you do when you change voltage is series or parallel the coils.  A 12 lead motor would give you the choice of wye or delta.


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## rdhem2

Mr. hasler, shall we try again?  You guys are so close yet so far away.  Forget the neutral when wiring motors.  Motor does not use it, does not care.  Motor name plate says 208/240v it can be wired either 208v WYE or 240v DELTA connected transformer.  Why don't we care?  Because it comes from the power company and you can do nothing about it anyway.  480/277v again forget the 277 as this is for a neutral connected item.  Motor is not connected to neutral so it is straight 480v connection.  480v grounded delta hook up has been illegal for years do to dangerous conditions in installations not properly supervised and maintained. 

When swapping phase legs for motor rotation.  Forget the wild leg.  All phases are 240v between legs.  Only when read to the neutral, electrical ground, or the ground wire, equipment ground does it manifest itself as 196v to ground.  When wiring a 240v single phase device, your welder, dryer, big hot plate, whatever, it does not matter which two legs you tap as they are all 240v leg to leg.  Get out you multimeter or even your wiggies and take some readings.  Maybe that is the best way to get it to come to reality.

Wild legs only matter when connecting a device to that leg and a neutral, electrical ground.  Equipment ground does not matter because it is only there for your safety anyway.  To carry away objectionable, dangerous, fault currents of short duration.

*Wild Leg only matters for 120v connections.*


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## John Hasler

rdhem2 said:


> Mr. hasler, shall we try again?  You guys are so close yet so far away.  Forget the neutral when wiring motors.  Motor does not use it, does not care.  Motor name plate says 208/240v it can be wired either 208v WYE or 240v DELTA connected transformer.



That's what I said:  The motor does not care how the transformer is wired: just what the line to line voltage is.  I also noted that I knew of no three phase motors that made any use of the neutral.


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## AlanR

Russ has it pretty much covered, not much to add except for some clarification, the primary reason for 208 wye to exist is to provide 120V circuits from a three phase wye leg to the center of the wye (neutral).

208V / 1.7320508 (the square root of 3) = 120V

I think this might be the "lightbulb" moment for the non electrically inclined.


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## nickmckinney

I seem to remember 240 across the outer legs and 240 from each outer to the center. The outers each read 120 to neutral and the center read 240 to neutral. Does this sound like a high (or hot?) leg? Going from memory from looking at it this weekend so I could be wrong somewhere. The 220/440 motor has 6 windings, right now 3 are parallel.


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## Kevinb71

Yes that sounds like High leg Delta from your description. Russ has already given you all the details so I won't reiterate it. His thoughts on a separate panel for the "single phase" loads is the only way we can do high  leg Delta here. Three phase loads in one panel and all single phase (240 and 120) in another panel. Just bring the two hot wires that are 120V to neutral and the neutral into that panel. 
Connect your 3 phase motor out of the 3 phase panel with one of the 3 hots to each leg of the motor and your motor will be very happy.


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## rdhem2

Mr. John Hasler.  By singling you out, I was trying to get the point across that you were indeed the closest to the truth or closest to the way it works and can be used.  NOT that you were in error!


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## nickmckinney

Yes we do have a separate panel for the "regular" stuff. Thanks a bunch guys, here is the little Italian baby I am going to wire first with the 3 phase. Its a combination stone surfacer, single point HSS/CBN surfacer, and flywheel grinder (once I can find that attachment) Think of a bed mill with a really wide powered X travel and single speed 13" diameter cutting head and thats basically it. Now with this 3 phase knowledge I can open my options on a larger lathe than I was originally thinking too.


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## TOOLMASTER

for years one of the shops i worked at had a 110 plug hidden behind a cabinet..we moved everything around one day..first thing one of the guys does is plug in his radio..poof..turns out it was hooked to the wild wire . apparently no one ever used it since the place opened.


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## nickmckinney

One last question (I hope) I found I have a run of 4 conductor wire that stopped about 5' short of the machine and was terminated, it must have been the original 3 phase install by the prior tenants. Its 12AWG solid. I found a calculator online and 208V with 7HP (cushion factor) calls out for 22A and 14AWG minimum. Would the electicians here feel comfortable direct connecting to this, it would be a total 45 foot run end to end, the last 7' feet is a flex 10AWG cable that was already on the machine.


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## AlanR

Why not? 12 GA is larger than 14 GA.


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## Kevinb71

5 hp at 230V would need at minimum #12. 7.5 hp at 230 volt would need #10. Your circuit should be OK, but without actually seeing the nameplate I couldn't say for sure. If you have a 20 amp breaker on the #12 in the panel where it is fed from you should have no problem. I assume that the machine has starters with overload protection built into it. Another issue that you haven't mentioned is how far the panel is from the machine for voltage drop. If I were running this circuit in new for you I would use #10. It's cheap insurance against any voltage drop issues. All that said it should run on the #12.


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## nickmckinney

AlanR said:


> Why not? 12 GA is larger than 14 GA.



Yeah but since this is my first 3 phase rewire I feel more comfortable confirming with those smarter than me. The same calculator said I could go as high as 40A for this which sounds like a lot to me on 12AWG. I think the short 50ft run is coming into play more than I would have thought.

Starting from scratch I had already priced out 10AWG but pulling a panel apart that had an emergency light right next to the machine I found the 4 conductor run. Its nearly in a perfect spot.

The panel is a "Square D" A pair of 3 phase breakers were unplugged and sitting in the bottom. One is a 20A and the other is a 30A. I quickly wondered if buying a lottery ticket should be purchased as this machine is hopefully going to fire up tomorrow about a month before I was expecting it.


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## rdhem2

WOW!!!!

Some calculator, it and the code book do not seem to agree on much.  #12 wire with THWN/THHN insulation is good for 20 amps.  Under continuous load situation (constant load of 4 hours or more)it is rated for 16 amps. Wire is good, of any size, for 80% if its full load rating when the load varies, such as a receptacle circuit.  There are lots of other sizing requirements also so error on the generous side of things.

There is a little book out there for about $16 that is a short read on a lot of the basics of wiring.  It is called
*UGLY'S ELECTRICAL REFERENCES by Geo. V. Hart*.  Well worth the money, makes things easier to understand, solves problems, has the answers to everyday problems and fits in your tool box so is always there.  It is not very thick, 3/8" or so , so it is not real intimidating!


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## AlanR

nickmckinney said:


> Yeah but since this is my first 3 phase rewire I feel more comfortable confirming with those smarter than me. The same calculator said I could go as high as 40A for this which sounds like a lot to me on 12AWG. I think the short 50ft run is coming into play more than I would have thought.


Just get a clamp on ammeter, HF sells them, Lowes, Home Depot etc.

Connect the thing up and measure the current(s), I think you'll be surprised with how good the margins are with what you have now. This stuff is not really that complicated, the ammeter will give you confidence and save you money.

edit: Search the sites I mentioned for "clamp meter".


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## jim18655

Table 430.250 minimum circuit size for  5HP 230v motor is 15.2 amps. So the short run of 12AWG would be OK, assuming there are no other adjustment factors to wire size, such as more than 3 current carrying conductors in the conduit. I would probably use #10 in a new installation since the cost difference would be minimal and allow future upgrades of equipment.
If the breaker is only for short circuit protection of the circuit then he could use the 40 amp breaker. See Table 430.52. 
Notes to Table 310.16 refer to section 240.4(D) which limits  small conductor to the commonly required overcurrent protection. However, it also refers to Table 240.4(G) which then allows other sections of the code to adjust overcurrent protection based on use of the circuit. Motors are specifically listed in Table 240.4(G). That allows the higher ratings in Table 430.52. Too small of breaker may cause nuisance tripping on motor start-up.
As long as there is proper overload protection at the motor he should be OK with the circuit.


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## DMS

I will second the recommendation of "Ugly's", it's very useful.

You have to be careful with those online calculators, and be sure you understand what they are giving you. There is a big difference between what a wire will handle in free air (like an extension cord), and what it will handle packed into a conduit with a bunch of other wires.


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## nickmckinney

Its just the four 12AWG wires in a 1/2 or 3/4" conduit. Nothing else is shared on this conduit. I am going to power it up as is just to test the machine and change to 10AWG when we tear the machine down for its upcoming mild refurb. I need to go through it before it gets serious service.


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