# 3-phase 120/240V Delta w/ center tap question



## micromind (Aug 11, 2007)

It would depend on the impedance and phase angle of the loads. 

If they were all resistive and balanced, I honestly don't know.


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## telsa (May 22, 2015)

All reference to ground is lost within the magnetic currents inside the transformers.

So your question becomes a nonsense question.

Remember that all transformers function like motor generator sets -- in alternating current. The magnetic circuit inside the coils ISOLATES the high and low voltages from each other.

That's why the neutral has to be bonded to the GEC System. That's what is setting neutral to zero potential voltage to the ground plane.


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## 460 Delta (May 9, 2018)

telsa said:


> All reference to ground is lost within the magnetic currents inside the transformers.
> 
> So your question becomes a nonsense question.
> 
> ...


It's not a nonsense question, especially if YOU aren't able to Google the answer to look like a genius. Things like this are how people think and dream who love this trade. This could be a foundational piece used by the OP or someone else to design a trick piece of gear.
If the Z were exactly matched on the loads like @micromind said, it may well be zero.
Paging @Pauleng paging @JRaef.


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## gpop (May 14, 2018)

crush1802 said:


> Theory question concerning a 3-phase 120/240V Delta w/ center tap neutral system. If you have 3 single phase loads sharing a neutral (one of which is the high leg), and you have an open neutral, what is the voltage of the neutral to ground?



You do not use the high leg to neutral.


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## splatz (May 23, 2015)

I don't think you'd ever share a neutral on a high leg for 120 A-N and C-N loads and 208V B-N loads. I don't think you'd get the cancellation you want on the neutral the way you do with a wye or 240/120. 

If you lift the neutral connection at the transformer on a 120/240 split phase service, it degenerates into a 240V series - parallel circuit. All the L1-N loads in parallel, all the L2-N in parallel, those two parallel circuits in series. 

If you are using B-N on a high leg delta for 208V, and lose the connection to N at the transformer, there has two paths through that 208V load. B-A through the A-N 120V loads, and B-C through the C-N (120V) loads. Those are of course 240V at a 60* phase angle. At which point I will just say it's all ****ed up and stop short of calculating anything.


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## paulengr (Oct 8, 2017)

In any system where you have floating wiring not physically connected to anything it is still “connected” but via capacitance and inductance. Generally speaking it is usually between the highest phase voltages so will be under 240 VAC as long as for instance it isn’t arcing. As soon as you connect/turn on a load it will be “shorted” to a phase and that equipment will see almost zero volts.

Usually in a 3 phase delta system with no faults that is reasonably balanced phase to ground is roughly 60% of the phase voltage but that’s only a rough number and doesn’t have to be that way. With everything floating no reason not to expect the same thing. That’s with most loads are 3 phase balanced. But throw in even on single phase line to line load and it all changes.


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