Using neutral from another transformer to get 277 from a 480v Delta transformer

This is a odd thing to ask and I'm sure it's not allowed, but I'm curious about the problems and effect from taking g a 480v Delta system (no neutral), adding a xformer that has a neutral, and using the transformers neutral with the preexisting 480v Delta system.

For the record, the second xformer is a step down to 240, but let's just pretend we are borrowing a neutral from another system.

Is this any better or worse than just using ground as the neutral?


Thanks!

For the record, I did not do this and 100 percent disapproved of it. It just sparked my interest in what would happen.

That's a very bad idea DO NOT DO IT.
the system will use the ground between the 2 transformers to carry the neutral return.
the voltage will float all over the place
and it will be huge shock hazard

You describe two different things:
1. Using the identified (neutral) conductor from an (assumption here) unrelated/connected system. This will cause voltage changes similar to those open neutral excercises from school (year 1 Electrical).
2. Transforming 480v delta to something with a neutral, this is quite do-able, depending on the results required. You could do a corner ground, high leg, etc.

Situation #2 is normal, #1 is not, primarily because you invalidate the purposes of the neutral and bond wires (safety!).

The proper way to get a neutral for all 3 lines is to use a Zig-Zag transformer. It has 3 line inputs and a neutral output. Then, ground the neutral.

If you have 3 equal loads, for example the windings of a motor, or 3 identical electric resistors then you can connect them in star connection and they will work at 277V.

But you should never use the other neutral !, the voltage that you will have between the delta transformer phase and that neutral is totally unknown.

I know not to do this. I'm just inquiring on what happens electrically.

One thing to keep in mind electrically -



The neutral coming from a different would be supplied by the power through that panels disconnect.



If that panel was locked out to service it or the machine, your neutral would cease to exist. AND - could possibly back-feed power through the neutral lead into the locked out panel and hurt someone.


Every machine I have worked on that had a neutral made had its own zig-Zag transformer for its own neutral. In a stamping plant that was about 20 presses each with their own.

Thanks for the feedback

May I ask what you need the neutral for ? Is it actually necessary ?

The machine had 480v going into it and used a neutral to create the 277 for other components outside of the motors.

The neutral was used to give them the 277. SO when they moved it to an area with no neutral, they were trying to create it by adding another xformer (step down 480 to 240) and using it's neutral in conjuction with the 480v wire to now have 277.

If they were going to do it incorrectly, they could have just used the ground and called it a day, but I was just inquiring on what happens when you do use the neutral from another xformer.


NOTE: I know this is illegal and stupid, but once again, I'm just curious what would happen.

Thanks!

Timeismoney08 said:

The machine had 480v going into it and used a neutral to create the 277 for other components outside of the motors.

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What are these "other components" ?
Do you actually need 3 phases of 277V ?

if I am understanding your post correctly, This is not allowed !
see the nec 70 code book, I cannot cite book chapter and verse.

GaryS is correct.

what you are proposing can do the following.
i'm a bit rusty on this.
the neutral you are proposing to use will carry the unbalanced phase current of the other transformer and could cause that neutral conductor to melt. that conductor is designed for the transformer it is connected to.

you will now have stray voltages all over the place and creating havoc. the 120 circuits with be all over the place. your voltage to ground WILL no longer be zero and WILL create a shock hazard and when the investigation is done, guess who is the fall guy for creating the problem.

if a short develops in one of the conductors of the other transformer, you can trip the main plant breaker, I had this happen at a printing press plant. it was a 4500 amp main, 23 other buckets and then from there other breakers.
it took 3 hours to find it and we had to remake all the printing plates, clean the printers. a big mess!

what ever the devices are that the transformer runs with no neutral, that's considered the owner of the devices.

if I am incorrect, someone please correct me.
james

JesperMP said:

What are these "other components" ?
Do you actually need 3 phases of 277V ?

Click to expand...

No, they do not need all of the phases for using with the neutral. Just one of them.

Components that need it are contactors, relays, etc.

Timeismoney08 said:

No, they do not need all of the phases for using with the neutral. Just one of them.

Components that need it are contactors, relays, etc.

Click to expand...

If it is a small consumption you can install a small 480V/277V transformer although It seems strange that you use 277V for the coils of a contactor or relay, better to use a 480/120V trafo or 480/24V ?