# high leg?



## truelight (Mar 17, 2010)

I have done mostly res in the recent years. I have a customer that has a shop. He has three ph coming in. He is considering purchasing some very expensive 3 ph equipment. The panel cover says high leg. He wants to know if everything will be ok. Is there any type of three phase that will not work with certain 3 ph equipment? I don't want to be respnsible for frying his equipment.

Thanks for your help.


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## 480sparky (Sep 20, 2007)

You need to be a bit more specific. Hooking up 480/277 three phase to a machine requiring 120/208 will tend to let all the magic smoke out.

What you need is the nameplate rating of the equipment and compare that to the service.


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## truelight (Mar 17, 2010)

He does not have 480/277 and I will ask him to get the name plate rating. I am pretty sure it will be rated for 120/208


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## don_resqcapt19 (Jul 18, 2010)

truelight said:


> He does not have 480/277 and I will ask him to get the name plate rating. I am pretty sure it will be rated for 120/208


 A high leg system has 240 phase to phase and not 208.


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## Shockdoc (Mar 4, 2010)

You need to be aware of its hook up, straight three phase w/ ground the equipment should be fine however if it's a three phase with neutral and ground careful attention must be paid to the leg(s) that require a neutral so they cannot be tied to the high leg or you will smoke controls and pc boards. You might need to do some alterations to the equipment if thats the case.


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## brian john (Mar 11, 2007)

If the equipment is rated 208/120 High leg an issue with the 120 as Shock noted.

PLUS if the equipment is rated 208/120 or 208 and you have 240, you MAY have an over voltage condition and will need a buck/boost transformer operated in the buck connection.


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## Southeast Power (Jan 18, 2009)

Do you have an electrician buddy that might have some commercial experience to work with you on this project? It sounds like you might need some support on this one.


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## brian john (Mar 11, 2007)

jrannis said:


> Do you have an electrician buddy that might have some commercial experience to work with you on this project? It sounds like you might need some support on this one.


 
Smoke while expensive, is a fast way to learn what not to do.:blink:


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## micromind (Aug 11, 2007)

As noted, if the equipment doesn't use the neutral, then the high leg will be OK.

If it does use the neutral, you'll need to figure out which terminal(s) involve the neutral, and put the high leg on one that doesn't.


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## Jlarson (Jun 28, 2009)

Gathering more information about the "equipment" is defiantly the first thing you want to do.



brian john said:


> Smoke while expensive, is a fast way to learn what not to do.:blink:


:laughing:


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## bahtah (Dec 21, 2010)

*Compatable Three-Phase*



truelight said:


> I have done mostly res in the recent years. I have a customer that has a shop. He has three ph coming in. He is considering purchasing some very expensive 3 ph equipment. The panel cover says high leg. He wants to know if everything will be ok. Is there any type of three phase that will not work with certain 3 ph equipment? I don't want to be responsible for frying his equipment.
> 
> Thanks for your help.


Any three-phase that does not meet the requirements of the nameplate on the equipment will not be compatible. Check to see what three-phase system is existing and then since he is just considering the equipment purchase he may be able to order the equipment to be compatible with the existing system. If not then you will have to determine what you will need to do to provide the power configuration required for the new equipment, deriving it from the existing system.


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## truelight (Mar 17, 2010)

OK. Are some three ph machines made to run with 3 ph Y ?

If it is, can it run on a 3 ph Delta?

Thanks guys for all your help.


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## micromind (Aug 11, 2007)

truelight said:


> OK. Are some three ph machines made to run with 3 ph Y ?
> 
> If it is, can it run on a 3 ph Delta?
> 
> Thanks guys for all your help.


Machines don't care if they're run on a wye or a delta connection provided the neutral is not involved. 

One notable exception is some VFDs and DC drives.. If the VFD or DC drive in question has MOVs that are connected phase to ground, it's possible that the high leg will cause a problem. 

Rob


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## electrolover (Feb 12, 2011)

must be an old shop


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## Skipp (May 23, 2010)

How many times have you come across a 3 phase machine/appliance that needed a neutral? Wouldn't it just have a control transformer for any needed 120 volts? Because no 3 phase motor is going to need a neutral.


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## jwjrw (Jan 14, 2010)

Skipp said:


> How many times have you come across a 3 phase machine/appliance that needed a neutral? Wouldn't it just have a control transformer for any needed 120 volts? Because no 3 phase motor is going to need a neutral.



I have installed a lot of 3 phase coffee and espresso machines require a neutral.


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## oldtimer (Jun 10, 2010)

jwjrw said:


> A lot 3 phase coffee and espresso machines require a neutral.


 


Indicating lights?

Controls?

Clocks?


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## jwjrw (Jan 14, 2010)

oldtimer said:


> Indicating lights?
> 
> Controls?
> 
> Clocks?



These new things are programmable to make many different drinks. I have no clue how they are wired internally but they all had 3 hots a neutral and a ground.


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## failelectric (May 27, 2010)

Call Manufacter


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## joebanana (Dec 21, 2010)

jwjrw said:


> These new things are programmable to make many different drinks. I have no clue how they are wired internally but they all had 3 hots a neutral and a ground.


Basically, a 3 phase water heater?
Where do you get 3 phase control?
Or, 3 phase lights?
Or, clocks?
An espresso machine with a 3 phase motor?


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## electrolover (Feb 12, 2011)

i hooked up some vavs that were 3 phase with a neutral.


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## jwjrw (Jan 14, 2010)

joebanana said:


> Basically, a 3 phase water heater?
> Where do you get 3 phase control?
> Or, 3 phase lights?
> Or, clocks?
> An espresso machine with a 3 phase motor?




I'll type slow since you seem to be slow......:jester:

I really didn't pay attention to the machines. I just know I bid the plans so I had the cut sheets and I did the install of the rough in wiring. Here is all I remember.

Several different coffee or maybe coffee grinder I don't remember. It was in 2007 and expresso machines

We were given cut sheets and they all required 20 amp 3 phase circuits with a neutral and ground

They were all fancy. Over 10k. I think the expresso machine was 12k. It had a computer inside????? Every time a drink was made it deducted the amount of each ingredient off your inventory. Did a bunch of other crap I have no idea about too.


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## 10492 (Jan 4, 2010)

Mydata My-9's are all 5 wire feeds.

At least the ones I have installed.


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## joebanana (Dec 21, 2010)

jwjrw said:


> I'll type slow since you seem to be slow......:jester:
> 
> I really didn't pay attention to the machines. I just know I bid the plans so I had the cut sheets and I did the install of the rough in wiring. Here is all I remember.
> 
> ...


I'm not arguing with the prints, I'm having wonderments about the logic behind it. Indicator lights are normally single phase, no? Okay, that covers the neutch. Control circuits, usually are DC, no? Don't make 3 phase DC. Clocks, hey, I'm not sayin' there aren't any 3 phase clocks, Just haven't seen any. Since "fixed in place" appliances require a ground, that covers that. What's left? Heating water, I guess 3 phase water heaters are more efficient than single phase, so why not?


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## CHECKtheE-STOP (Jan 17, 2011)

truelight said:


> I have done mostly res in the recent years. I have a customer that has a shop. He has three ph coming in. He is considering purchasing some very expensive 3 ph equipment. The panel cover says high leg. He wants to know if everything will be ok. Is there any type of three phase that will not work with certain 3 ph equipment? I don't want to be respnsible for frying his equipment.
> 
> Thanks for your help.


The reason for them labeling it high leg is because they have not pulled power from that phase for use in the 110v controls. Phase to phase the voltage will be the same but phase to ground or neutral one leg will be 208v while the other two will be 110v. If the high leg gets wired into the controls...... It can be a very costly fix.


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