# 480v high leg(?) delta



## jeremievc

I meant "to".


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## wildleg

no .


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## stars13bars2

what transformers are you using to get 480v high leg delta? :001_huh:


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## JRaef

Never heard of it.

Open leg (Open Delta) maybe?

Please describe the context of this, where are you getting the idea that you have "480V High Leg Delta"?


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## jeremievc

It is a service a customer had put in for an electric submersible pump. There are two transformers on the pole, each putting out 240ish volts to two legs and tied in together somehow to make up a third leg at about 480v.


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## jeremievc

It is just a guess at what the voltage is actually called, please forgive my ignorance.


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## jeremievc

460 between phases


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## JRaef

Hmmm... a quick Google search brings up some references in DIY sites where some people apparently refer to 480/277 as "High Leg", but that would NOT be a Delta service, that is Wye. So it is for DIY sites I guess. No big surprise.

There is such a thing as 240/120V 3 phase 4 wire service which is often called "High Leg", "Stinger Leg" or Red Leg" delta. In that arrangement it is a Delta transformer in which one of the 3 delta windings, usually A-C, is center tapped and grounded for a neutral so that you have 240V Line to Line from A to C and 120V between either end and neutral. The "High Leg" name comes from the fact that the phase to ground voltage on the remaining leg, i.e. B phase, has no reference to ground and so will float at around 80% of the L-L voltage, i.e. 215V on a 240V service. If you try to connect a single pole breaker to it, you get "stung".

480/277V is totally different. It's a true Wye service where any phase to neutral is going to be 277V.


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## MDShunk

480 open delta? Yuk. :blink: Didn't even know it was done.


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## jeremievc

480 open delta, thank you.


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## jeremievc

Is there any reason this type of voltage would affect the performance of longevity of a motor?


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## JRaef

jeremievc said:


> It is a service a customer had put in for an electric submersible pump. There are two transformers on the pole, each putting out 240ish volts to two legs and tied in together somehow to make up a third leg at about 480v.


Sounds like an Open Delta. You are probably measuring 240V line to ground, which is erroneous. The two transformers are making up a 480V delta service with an open jaw. It's less efficient so the transformers have to be over sized to avoid a serious imbalance, but it saves on the cost of the 3rd transformer and more importantly on far flung sites, that 3rd wire on the primary side for the utility.


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## JRaef

jeremievc said:


> Is there any reason this type of voltage would affect the performance of longevity of a motor?


Yes, the voltage is often not balanced very well and I'm suprised an ESP would allow it. Has the owner checked with the pump supplier? Some of them, such as Franklin, will void the warranty if there is more than a 2% phase voltage imbalance. But he may not have a choice anyway, the cost of that third wire might be ridiculously prohibitive, as in 10's of thousands of dollars.


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## micromind

Think of it as a 120/240 3ø 4 wire open delta, but operating at double the voltage.

I've seen two of these so far, both supplying 3ø motors in remote locations.


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## stars13bars2

seen plenty of 120/240 open deltas but never a 240/480 open delta. now I know they are out there somewhere.


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## jeremievc

It was my first time seeing it. This was about a two mile run made specifically for an ESP set in a wet well that is fed by a natural water source. The property owner is quite wealthy and has a system of piping and valves supplying various ponds and water features on his property. Really something to behold quite frankly.


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## Southeast Power

jeremievc said:


> How will this type of 480 three phase affect a motor? Will the high leg toast the winding it is attached yo?


If you are getting 460 phase to phase, how would that be a problem for the motor?


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## micromind

jrannis said:


> If you are getting 460 phase to phase, how would that be a problem for the motor?


A 3ø motor cares about phase to phase voltage. Nothing else. It doesn't care about any voltage to ground.....well, within reason.......

If the supply is a grounded delta, 3 wire or four, it doesn't matter at all which lead is connected to the grounded phase or the high leg.


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## JRaef

micromind said:


> A 3ø motor cares about phase to phase voltage. Nothing else. ....


But motors do care about voltage BALANCE, because unbalanced voltage creates negative sequence currents that cause counter rotating torque in the rotor which acts against the normal torque. That means that for any given amount of power, the motor is going to heat up more rapidly and it's entirely possible to burn up a motor without ever exceeding the FLC, so the overload relays don't protect it. That's why a lot of ESP (Electric Submersible Pump) mfrs don't allow more than a 2% voltage imbalance, they don't have any "fudge factor" designed into their motors (because of size and weight that would entail). 

Open Delta power systems are inherently unbalanced, but the amount varies with loading on the transformers. If the utility over sized the transformers enough it may be OK enough for that ESP, but I almost NEVER see that happen. 

So jeremievc,
If you want to look out for your customer, take a voltage reading *under load* and if there is more than a 2% imbalance, let him know that if the pump motor smokes, the ESP mfr may not honor their warranty. Many of them are like that, Franklin, the largest, is one of them.


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## kaboler

So is there a 480 delta? I would like to know what the numbers are phase to phase and phase to ground please.


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## micromind

kaboler said:


> So is there a 480 delta? I would like to know what the numbers are phase to phase and phase to ground please.


480 3ø 4 wire delta systems do indeed exist.

The theoretical voltages would be 480 from any phase to any other phase, 240 from A to ground/neutral, 416 from B to ground, and 240 from C to ground.


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## JRaef

kaboler said:


> So is there a 480 delta? I would like to know what the numbers are phase to phase and phase to ground please.


Phase to phase, 480V.
Phase to ground voltage varies, there is no ground reference. In a perfect world you can expect it to be 277V by thinking of each measurement connection to ground as being a virtual capacitor with all three of them tied together at ground, but any slight difference in circuit impedance, natural or otherwise, will result in three different voltage readings from phase to ground, rendering that measurement pointless. It's hard to explain in a paragraph, just remember in a true ungrounded Delta system, phase to ground voltage measurements are meaningless.


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## budmax

what I have seen that the A leg to ground 277v B leg 480 v to ground c leg 277 v to ground to each phase it would be 480v. In the transformer yard the middle trans would be centered tap to ground on the sec side.


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## EJPHI

JRaef said:


> .
> 
> ...... The "High Leg" name comes from the fact that the phase to ground voltage on the remaining leg, i.e. B phase, has no reference to ground and so will float at around 80% of the L-L voltage, i.e. 215V on a 240V service....
> 
> JRaef
> 
> Since the neutral is grounded there is in fact a ground reference so the B leg would be at 120<0 +240<120 =208<90 which is about what you got. I guess I don't understand you description of the B leg as floating.
> 
> Please enlighten me.
> 
> EJPHI


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## micromind

EJPHI said:


> JRaef said:
> 
> 
> 
> .
> 
> ...... The "High Leg" name comes from the fact that the phase to ground voltage on the remaining leg, i.e. B phase, has no reference to ground and so will float at around 80% of the L-L voltage, i.e. 215V on a 240V service....
> 
> JRaef
> 
> Since the neutral is grounded there is in fact a ground reference so the B leg would be at 120<0 +240<120 =208<90 which is about what you got. I guess I don't understand you description of the B leg as floating.
> 
> Please enlighten me.
> 
> EJPHI
> 
> 
> 
> JRaef is referring to a system that is not grounded at all. In this system, voltage to ground is unpredictable.
> 
> Usually a 3ø 3 wire system, and ungrounded is legal only if there is some sort of ground detection system in place.
> 
> If it's 3ø 4 wire, then it has a high leg. If it's 3ø 3 wire it doesn't.
Click to expand...


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## EJPHI

Thanks Micromind.

My confusion came from the idea that a 4 wire delta will have a ground reference from the center tapped A-C winding. Normal delta (3 Wire) would not have this reference and would only rely on stray capacitance and leakage to establish the phase to ground potential. 

EJPHI


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## EJPHI

I forgot to mention that grounded 3 wire delta would also have a ground reference of course!! Japanese customers of my former employer used grounded delta in their semiconditor FABs.

EJPHI


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