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#201652 - 06/14/11 11:02 PM Neutral required?  
Yoopersup  Offline
Member
Joined: Mar 2003
Posts: 830
Michigan
4160 over head to pole mounted transformer. Feeder NOT Service. Secondary 480/277 . Run dn pole with 3 hots & Ground sized by 250.66 .
I say must be 3 hots plus Neutral.
Need neutral to be able to ground at building.
Remember NOT SERVICE conductors , Owner ownes 4160 pole line.
Whatca Think??
Please give code Sections Yoopersup


2017 / 2014 NEC & Related Books and Study Guides

#201655 - 06/15/11 12:05 AM Re: Neutral required? [Re: Yoopersup]  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Where is there any requirement for any type of circuit to have a neutral?


#201657 - 06/15/11 12:19 AM Re: Neutral required? [Re: Yoopersup]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,123
Estero,Fl,usa
There is no requirement to bring a neutral out of the service disconnect enclosure as long as there is no neutral load. It was very common in computer room panels not to have a neutral.

You still need the EGC.


Greg Fretwell

#201661 - 06/15/11 04:42 AM Re: Neutral required? [Re: Yoopersup]  
frenchelectrican  Offline
Member
Joined: Feb 2003
Posts: 939
Wi/ Paris France { France for ...
Originally Posted by Yoopersup
4160 over head to pole mounted transformer. Feeder NOT Service. Secondary 480/277 . Run dn pole with 3 hots & Ground sized by 250.66 .
I say must be 3 hots plus Neutral.
Need neutral to be able to ground at building.
Remember NOT SERVICE conductors , Owner ownes 4160 pole line.
Whatca Think??
Please give code Sections Yoopersup


This is a fine line to cross with MV primary side and as long you see the 4160 is used as delta you only need to bring the EGC that it but just beaware with the NESC requirement on MV side for disconnect and O/L requrment on primary side of transfomer but for secondary side you have to treat them as SDS.

Merci,
Marc

Last edited by frenchelectrican; 06/15/11 04:44 AM.

Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)


#201671 - 06/15/11 08:04 PM Re: Neutral required? [Re: Yoopersup]  
Yoopersup  Offline
Member
Joined: Mar 2003
Posts: 830
Michigan
I know past the Main a Neutrals not required but this is on the secondary side of a Transformer. Yer taking Ground off XO of a transformer???? I feel it should be called a Neutral, Landed on a Neutral bar Bonded to Panel then Grounding Electriod run to that bar. Its really the same but called a Neutral.
If there wasn;t a transformer on the other side then Calling it a Ground would be no problem.


#201683 - 06/16/11 01:30 PM Re: Neutral required? [Re: Yoopersup]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,123
Estero,Fl,usa
You say 480/277 but, is there any 277 load?

If this is simply feeding 480 L/L loads, why do you need a neutral? You are center tap "grounding" the transformer at the XO but that is not really a neutral until you put a neutral load on it.


Greg Fretwell

#201687 - 06/16/11 09:55 PM Re: Neutral required? [Re: Yoopersup]  
Yoopersup  Offline
Member
Joined: Mar 2003
Posts: 830
Michigan
My point is per 250.24 (C) Operating less then 1000 volts is grounded at any point. Grounded conductor SHALL be run to each disconnecting means.Yes this is aimed at Service equipment BUT. if you put a 4160 transformer 3 phase on a POLE , run secondary down to a Disconnect 225.8 (C) Grounded conductor must be broken. Not Grounding conductor.
Yes it a FEEDER but for grounding purposes I feel it should be a grounded conductor. Only difference is it might be sized a bit larger & be white, Then the Grounding Electrod conductor would go to the disconnect & be bonded there. Either way you do it you have 480/277 at the disconnect. But with the Neutral you have a True 277/480 with a Ground you have 480 with ground .Kinda get what I;m saying here??


#201688 - 06/16/11 11:57 PM Re: Neutral required? [Re: Yoopersup]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,123
Estero,Fl,usa
250.24 is written that way because that is where the main bonding jumper has to be.
In reality you still only have 3 wires coming there on any single phase service and 4 wires on 3p. I am reading you to say you want 5 wires. That implies the main bonding jumper is somewhere upstream on the line side.

Last edited by gfretwell; 06/16/11 11:58 PM.

Greg Fretwell

#201691 - 06/17/11 03:50 AM Re: Neutral required? [Re: Yoopersup]  
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,708
Anaheim, CA. USA
I understand why Yoopersup is concerned with this setup.
It appears as if there is no _Direct Bond_ between the Metallic Enclosures on the Separately Derived System (SDS), and the Star point of the Transformer Array.

If this is accurate, then the SDS is an Ungrounded 480V 3 Phase 3 Wire; instead of being a Delta Configuration, it is a Wye Configuration.

As long as there is a local Grounding Electrode System bonded to the Metallic Enclosures on the SDS, the System is safe and conforms to NEC Article 250.

HOWEVER...

If the Star Point is tapped, with a 4th Conductor brought down from the Wye Network to the first Disconnect... AND this Conductor is usable for a "Dual Voltage SDS" (480Y/277V 3 Ph. 4 Wire), then the tap from the Star Point shall be a Grounded Conductor for the SDS, requiring all the Bonding and similar stuff.
This Grounded Conductor would need to be brought to the first "Supply Point"

Other Possible Grounding Options:

A: Star Point Ground Bonded At Pole...

The SDS might be Ground Bonded at the Pole, via a Grounding Electrode Conductor (GEC) directly Bonded to the Star Point at the Secondary.
Same GEC is also bonded to metallic enclosures on the SDS.

B: Corner Grounded SDS...

One of the Three Phase Lines may be Grounded either at the Pole, or at the first Disconnect / Supply Point.

C: Impedance Grounded System...

Either via an introduced Impedance between Grounding Electrode System (GES) and the Star Point of the Transformer Network (proper),

or;

No Physical Connection between the GES and the Star Point of the Pole Mounted Transformers - AKA Impedance of the Dirt. (not preferred, but have seen several of these!)

FYI: The "Star Point" is the common termination of all Three Secondary "X2" leads, from all Three Transformers.

[Linked Image]
The Yellow Common Connection on the Secondary side of this Drawing is the "Star Point". It is where the Common Grounded "Neutral" Conductor is derived for the 4 Wire Wye.

* BTW Yoopersup: Are the Transformers for this System connected as shown in the above drawing...,

or;

like one of the configurations found on the following pages:

3 Phase 3 Wire Wye

3 Phase 3 Wire Closed Delta

(click on the blue underlined text to jump to that page).

-- Scott


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#201692 - 06/17/11 09:14 AM Re: Neutral required? [Re: Yoopersup]  
Yoopersup  Offline
Member
Joined: Mar 2003
Posts: 830
Michigan
What I;m saying is From the pole mounted Transformer down the Pole should be the 3 phases & a Neutral conductor(same as a utility company would do to the building underground via PVC ).(ground rod installed at pole location which is remote from building) Then at the main service rated disconnect(at the building) a bonding jumper installed, (same as utility company again) then grounding Electrod conductor installed as per code. That way you have a 480/277 at the ist disconnect for correct grounding.

I don't see a need for running both a neutral & a ground dn the pole to the ist disconnect switch But it could be done if Neutral floated at that panel.


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