# Converting a 3 wire 3 phase aux panel to 4 wire



## scotch (Oct 17, 2013)

Noticed that no one commented on your post....
Suffice to say what you want to do is dangerous ....that's why no one else in the trade that understands electrical does it. !!


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## joebanana (Dec 21, 2010)

Dude, rent a generator. You don't need to be playin' in the panel.


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## Southeast Power (Jan 18, 2009)

Elec Trix said:


> Long-time listener, first-time caller. Please be gentle
> 
> I have a 200 amp, 240 volt, 3 phase auxiliary panel with 3 #3/0 copper ungrounded (hot) conductors and a #4 copper grounding (ground) wire to a non-insulated ground bar bonded to the panel. I would like to add some 120-volt circuits to this panel. This auxiliary panel is fed via 3" rigid conduit. I would like to covert the #4 grounding wire to a grounded neutral, and let the rigid conduit serve as the grounding conductor. I plan to install an insulated ground bar in the auxiliary panel and move the #4 grounding wire to this insulated ground bar which would now be the grounded (neutral for my new 120 volt circuits). I would limit my 120-volt breakers to 80 amps, so the unbalanced load would never be more than 80 amps, most likely far less if I balance the 120 volt loads across the 3 phases.
> 
> ...


I see what you are trying to do and I think I would do it the same way.


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## brian john (Mar 11, 2007)

STRICTLY Temporary, and the neutral current was low I'd do the same thing.

WORK SAFE.


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## sbrn33 (Mar 15, 2007)

Hell I don't even care if is temp. I would do it label it and call it good. Just remember that it is probably a Delta so check you voltages before you blow up these "temp" loads.


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## B-Nabs (Jun 4, 2014)

Is it a Wye service? Is there a neutral at these disconnects you're taking about? 

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## B-Nabs (Jun 4, 2014)

sbrn33 said:


> Hell I don't even care if is temp. I would do it label it and call it good. Just remember that it is probably a Delta so check you voltages before you blow up these "temp" loads.


Beat me to it. 

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## sbrn33 (Mar 15, 2007)

I might get some split grounding bushings and make sure the ground was good.


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## paulengr (Oct 8, 2017)

If it's a delta panel, there is no transformer"neutral". There are four ways to fix this. Either use a special zigzag transformer or a delta-wye 1:1 transformer. Either way the output of the transformer is a neutral. The third way is to wire up a delta-wye transformer and use all 4 wires on the output (three phases and a neutral) to do whatever you want. The fourth way is to put a single phase transformer on two of the phase legs and get whatever voltage you want out.

If it's a wye and solidly grounded then the ground may be connected back to the neutral directly or it might be a peg ground (just a ground rod...no connection). Peg grounds are really bad practice but common in older plants. Best bet is to pull a neutral yourself all the way back to the transformer which also meets Code. Of course you can also establish a new separately derived system/neutral using the same tricks that work on a delta system.

None of these are quick and cheap....not really "temporary" in any way. Cheap and simple is to rent or buy a generator or a welder or a light plant.

One of the first things I do when I go to a plant when I'm dealing with strange voltage issues, transformers, etc., is to walk up to the transformer and check the name plate for whether it's delta or wye. Even if it's utility owned, I have the utility socket and just open the door to peek at the name plate mounted inside the unit. Most of the time even if I ask the plant whether they are delta or wye, they get the question wrong. That's kind of sad when you think about it because the guys working on this stuff should know about the utility feed. Also wye-wye transformers are VERY popular with some utilities around here. That is kind of like having herpes when it comes to ground faults...you are going to be sharing every ground fault with the utility and vice versa. It's an incurable disease that will cause constant problems with your plant forever.


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## Southeast Power (Jan 18, 2009)

I had to assume he had a neutral to work with.


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