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#207644 11/15/12 12:08 PM
Joined: Mar 2003
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All by Owner Utility not involved.
2500 KVA 13.8 Pri. 480/277 Sec.
Transformer outside Bldg. Switchgear inside.
Switchgear Must be service rated.(225.36)
Question ?? Since transformers a 480/277 Volt sec.
Can Switchgear be Straight 480 volt with Ground??
I say since its a Y grounded system , A Neutral must be brought to the Ist Switch as required in 250.24(C).
Otherwise you have Y transformer Delta Gear.
This would not apply past ist Switch.
Neutral required for proper grounding at ist switch only.
I've looked at several Forums & articles .
I know the Neutral is not used for any other purpose then grounding.
If straight 480 v Gear put in on Switchgear. Nameplate would read 480 v 3 wire / Transformer would read 480/277 v 4 wire.
Again this would only apply to ist switch entering the building. Past that 3 hots Gr. OK.
Yoopersup

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Joined: Jul 2001
Posts: 599
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You are correct.

Gear with a neutral in the one section only is not uncommon. Almost every '4W' Motor Control Center is built this way.

If you want a UL SE label the gear will need to include a neutral-ground bonding method as well as a neutral isolation link.

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Yoop:
You got it. Over here the utility requires 4 wire.(Period)



John
Joined: Jul 2004
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It would not be delta since the secondary is grounded at the center point of the 3 windings.

You are probably in 250.30(A)(8) for an SDS.
Quote

(8) Grounded Conductor. Where a grounded conductor is installed and the system bonding jumper connection is not located at the source of the separately derived system, 250.30(A)(8)(a), (A)(8)(b), and (A)(8)(c) shall apply.


a, b & c refer to sizing.

If the bonding jumper is in the transformer enclosure, it can be argued that you do not need to extend the ungrounded conductor.


Greg Fretwell
Joined: Mar 2003
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I know its not a Delta but 3phase 3 wire on gear would make U think so.
Without a Neutral running to the gear how do you get Fault current to the transformer XO.
The Transformers outside on the building.
250.8(A) says :
Where a Grounded conductor is installed.
There saying it can be a Grounding conductor. Not Grounded conductor.
Also as Transformers a Y 480/277 the Gear should be service rated & match.

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Fault current will flow the same way it always does, down the EGC to the bonding jumper, which is at the transformer from your description.

I do not believe the disconnect in the second building is "service equipment" as referenced in 250.24 even if it has to have an equivalent rating.
Service equipment is defined as being at the "load end of service conductors" in article 100.
The feeder conductors from the transformer are not "service conductors"

That is just my opinion.


Greg Fretwell
Joined: Mar 2003
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Greg
Yep its a Feeder by Definition And a SDS. But 250.24 explains it best. I talked to Several about it.
Yer Reference to 250.8 is correct.
See Definitions :
Grounded conductor
Grounding conductor .
It by definition is a Grounded conductor.
Yoopersup

Joined: Jul 2004
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Your patch, your rules.
I am just not sure why you bring a neutral to a load side disconnect if there is nothing connected to the neutral. I a can understand coming to the service equipment but this is not service equipment. I don't think 250.24 applies.

If you look at 250.30(A)(1) it says the bonding jumper can be anywhere from the source to the first disconnect. Is it bonded in the transformer enclosure?
If that is true I see no reason to bring a grounded (AKA neutral) conductor any farther if you have no neutral loads.

In fact they have pictures in the handbook of several transformers in a building, all bonded in the transformer enclosure.

I would agree it is a good design idea in case their plans change and they want a 277 load served but I am not sure it is absolutely required by code.



Greg Fretwell
Joined: Mar 2003
Posts: 849
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Grounded separately derived systems include six basic components in the grounding and bonding scheme:(1) the system bonding jumper, (2) equipment grounding conductor [primary side of transformer-type derived systems], (3) the equipment bonding jumper, (4) the grounded conductor, (5) the grounding electrode conductor, and (6) the grounding electrode.

Look up Definitions of a Grounded conductor.

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Quote
Grounded Conductor. A system or circuit conductor that is intentionally grounded.


Is the transformer secondary grounded in the transformer enclosure (XO bonded to the GEC and EGC via the bonding jumper)?

If so, what function would extending a grounded conductor any farther than that serve, since there is no unbalanced circuit load?


Greg Fretwell
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