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#71936 - 11/10/06 10:02 PM 75KVA Transformer  
WiCeltic  Offline
Member
Joined: Oct 2001
Posts: 20
Sheboygan, Wi. USA
Installing a 75kva transformer, 3 Phase, 440V delta Primary; Wye 208/120V secondary. Transformer feeds 225A 3phase 208/120V panel. The customer is ONLY running 3phase 208V machines. Everything will be 3 phase in the panel. There are other panels to get 120V out of. Would you run the neutral wire from the transformer secondary to loadcenter panel?
Thanks in advance!!


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#71937 - 11/10/06 10:10 PM Re: 75KVA Transformer  
NJwirenut  Offline
Member
Joined: Sep 2001
Posts: 806
Bergen County, NJ
If it was my own facility? Absolutely, so that I would have maximum flexibility for future additions.

For a customer? Only if they are willing to pay for it or it was in the spec/bid. Assuming the conduits are big enough for another wire, the only additional cost is one more conductor, plus the time needed to make 2 more terminations. Buys a lot of "futureproofing" for a small incremental cost.

If the panel is called out as "208/120V", then I would argue that the presence of a neutral is implied, even if unused. If the panel is only specified as "208V", then no neutral.

[This message has been edited by NJwirenut (edited 11-10-2006).]


#71938 - 11/10/06 10:30 PM Re: 75KVA Transformer  
SteveFehr  Offline
Member
Joined: Mar 2005
Posts: 1,208
Chesapeake, VA
I'd run the neutral just to future-proof. If the job was over budget, I might potentially cut it out, but I'd size the conduit so we could put it in later if necessary. But if I were in your place, I'd run the neutral.

[This message has been edited by SteveFehr (edited 11-10-2006).]


#71939 - 11/11/06 07:41 AM Re: 75KVA Transformer  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
I am not into giving things away but I would probably provide the neutral and here is Wye. [Linked Image]

You already paid for a Delta/Wye transformer when a delta / delta would have done it.

I also assume you are not planing on ungrounded delta at this new panel.

That being the case your required to bond XO to ground, building steel etc even if you never use the neutral.

And finally, in most cases the panel is located very closely to the transformer.

Considering the money and labor already put out the cost of a few more feet of conductor should not be a big deal.

My opinion might change is the distance is long.

One last thing....what is shown on the prints, specs or job scope?


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#71940 - 11/11/06 03:50 PM Re: 75KVA Transformer  
mxslick  Offline
Member
Joined: Oct 2004
Posts: 803
Atomic City, ID USA
Quote
Transformer feeds 225A 3phase 208/120V panel.


Strictly from my amateur point of view, if the panel is labeled as 3phase 208/120v, wouldn't you be required to feed it as such, even if the planned loads are only going to be 208v?

Quote
My opinion might change is the distance is long.


Mine doesn't. [Linked Image] But then again, I don't share neutrals either. [Linked Image]

edited to change "connect" to "feed".

[This message has been edited by mxslick (edited 11-11-2006).]


Stupid should be painful.

#71941 - 11/11/06 04:23 PM Re: 75KVA Transformer  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Quote
if the panel is labeled as 3phase 208/120v,wouldn't you be required to feed it as such,


I don't think so.

Any more than you have to feed a 225 amp panel with 225 amps.

Or any more than you have to supply a Square D I line at 600 volts just because it is able to handle that voltage.

IMO where you would run into trouble is when you try to supply a straight three phase panel with Wye.

Quote
But then again, I don't share neutrals either.


Actually you share neutrals with every circuit on the supply side of the source.

Electrons do not know or care which side of a panel they are, they act the same either way.

You can deny it to be true if you want but I challenge you to show how it differers electrically from one side of a panel to the another.

BTW I had to bring two branch circuits to each of two 9 panel LED screens at a concert venue.

You'll never guess what the vendor specified.

An L21-30R

[Linked Image]

Thats 3 hots with one neutral for those following along at home. [Linked Image]

It worked flawlessly and aided in combating voltage drop on the 400' runs of 6 AWG. [Linked Image]



[This message has been edited by iwire (edited 11-11-2006).]


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#71942 - 11/17/06 09:49 PM Re: 75KVA Transformer  
mxslick  Offline
Member
Joined: Oct 2004
Posts: 803
Atomic City, ID USA
Quote
Or any more than you have to supply a Square D I line at 600 volts just because it is able to handle that voltage.


True, but isn't there a Code requirement that states that panels shall be clearly marked to indicate the supply voltage? [Linked Image]

The OP's situation, omitting the neutral when the loadcenter's labeling indicates that it is a 208y/120 tells me that unless you change the labeling to clearly indicate that it is being used as a "straight" 208y loadcenter, you will have a Code violation.

(Side note - I'll dig thru my '99 NEC to get a reference, if I locate what I had in mind I'll edit this post.)


Numbers in following quote added by me.

Quote
(1)Actually you share neutrals with every circuit on the supply side of the source.

(2)Electrons do not know or care which side of a panel they are, they act the same either way.

(3)You can deny it to be true if you want but I challenge you to show how it differers electrically from one side of a panel to the another.


LOL Bob, I love how we can agree to disagree. [Linked Image]

To whit:

(1) Absolutely. But at that point you have larger conductors, lower impedance to the neutral point of the transformer and/or ground, and the benefit of load diversity and the effects of motors and resistive loads to help "even out the bumps" so to speak.

With branch circuits, you don't have those same conditions. I think we can both agree that differences in conductor size, length, ampacity, even wiring method (conduit, open air, romex, even routing) can have some effect on circuit performance, however slight.

(2) Uh... maybe, maybe not. I don't fully understand the physics of electricity and I'm sure there are many EE's who can tell stories of things that should never happen but do. So I take the middle ground on that one.

(3) I deny nothing, but I also challenge anyone to explain why, in my line of work, that shared neutrals cause trouble in audio and microprocessor control systems, and the use of dedicated neutrals solves/prevents those issues.

Because candidly, like any other person in business, if I can save costs while providing the performance standards my clients demand, I'm all for it. But in over 20 years of cinema and professional audio, no one has ever come up with the explanation that will allow me to share neutrals on the branch circuits without any issues. And I will not compromise my standards for system performance to save even a few hundred in wire cost.

Now the "isolated" vs. "non-isolated" grounding thing is a whole different ballgame. I have, so far anyway, found NO benefit to the use of isolated grounds. Proper audio wiring techniques take care of any grounding issues.

The LED screens in your example I would have supplied the same way with no quibbles. For one, all the reasons you point out are valid, and the savings significant. And you weren't dealing with audio signals and the high gain involved.

However, I challenge you to supply a few racks full of high-powered audio amplifiers that way and see what happens. [Linked Image]

Bear in mind that in my challenge I realize that the potential increase in hum or other noise issues that can result won't matter in a large venue, but try to get away with that in the media room of a multi-million dolar home!

So we're working in different areas, and what works best for me is too costly (and understandibly so) in someone else's area. But as long as the client's happy when we're done, that's what really matters, right? [Linked Image]


Stupid should be painful.


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