Derived Neutral

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Mike01

Mike01

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:-? question: If you have a facility, (large plant) with multiple substations located on the roof and a lighting panel is to be located in the roof penthouse also however the panel (480/277v-3ph-4w) will be fed from a adjacent switchboard feed from a 1600A breaker located in the substation the problem I have is the person that laid out the substations specified them as 3ph-3w, now that I need to add a lighting panel what would be the best way to get a neutral to the panelboard? I would hate to install a xfmr 225kva 480delta-480wye just for a neutral conductor any suggestions. The reason is the plat lighting is high bay fluorescent. do they make fluorescent ballasts 480v-1ph?? any suggestions. thanks in advance.
 
thanks

thanks

the high bays are equiped with 2-54wt5ho lamps each, if that is the case could I put in a 480v-3w panelboard (do they make these I assume it is the same as a 480/277v except without the neutral), and connect all my fixtures at 480v-1ph. or would I be better off trying to derive a neutral from some where?
 
Mike01 said:
the high bays are equiped with 2-54wt5ho lamps each, if that is the case could I put in a 480v-3w panelboard (do they make these I assume it is the same as a 480/277v except without the neutral), and connect all my fixtures at 480v-1ph. or would I be better off trying to derive a neutral from some where?
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I guess that's a design issue you'd have to sort out yourself by poking the calculator a little bit. Cost of fixtures with 480 ballasts versus a transformer. It's funny that just by chance I linked to the exact ballast you'd need if you went that route.
 
Mike01 said:
:-? question: If you have a facility, (large plant) with multiple substations located on the roof and a lighting panel is to be located in the roof penthouse also however the panel (480/277v-3ph-4w) will be fed from a adjacent switchboard feed from a 1600A breaker located in the substation the problem I have is the person that laid out the substations specified them as 3ph-3w, now that I need to add a lighting panel what would be the best way to get a neutral to the panelboard? I would hate to install a xfmr 225kva 480delta-480wye just for a neutral conductor any suggestions. The reason is the plat lighting is high bay fluorescent. do they make fluorescent ballasts 480v-1ph?? any suggestions. thanks in advance.
Click to expand...

You can't just conjure a neutral from the delta out of thin air. If you want a neutral, the delta-wye transformer is the way to do it.

Vern
 
Mike01 said:
the high bays are equiped with 2-54wt5ho lamps each, if that is the case could I put in a 480v-3w panelboard (do they make these I assume it is the same as a 480/277v except without the neutral), and connect all my fixtures at 480v-1ph. or would I be better off trying to derive a neutral from some where?
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Most 3P-4W panelboards I've seen are specifically rated for 3P-3W as well, you just ignore the neutral connection.

Vern
 
VernB said:
You can't just conjure a neutral from the delta out of thin air. If you want a neutral, the delta-wye transformer is the way to do it.

Vern
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Not quite 'thin air', but there are several ways to add a neutral other than a delta-wye transformer. Look up 'zig-zag' transformer, for example.

I don't believe that any of the non-isolated derived neutral approaches would be applicable to the original poster's requirements, because of grounding and bonding issues; but they do exist.

-Jon
 
winnie said:
Not quite 'thin air', but there are several ways to add a neutral other than a delta-wye transformer. Look up 'zig-zag' transformer, for example.

I don't believe that any of the non-isolated derived neutral approaches would be applicable to the original poster's requirements, because of grounding and bonding issues; but they do exist.

-Jon
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Ah, but my understanding is that a zigzag is only used to provide a return path for earth faults on a delta (by providing an earth reference point) and can't be used for supplying load. The original poster specifically stated he was looking to create a neutral for operating lighting, ala 480Y277, which is why I didn't suggest a zigzag.

Vern
 
I see no _physics_ reason that a suitably sized zig-zag transformer could not be used to provide a neutral to feed a load. However I see a number of code issues that I don't know the answer to.

I see no problem using a suitably sized zig-zag transformer _at the location of the delta secondary_ to convert a 3 wire delta system into a solidly grounded 4 wire system with a neutral, and then feeding loads with that neutral. (Note, however, that I have not examined the code implications fully, and there is probably an issue that I don't see.)

But if you have a three wire feeder from an ungrounded delta, and you add a zig-zag transformer, I don't see how you could properly bond the system and use the neutral. If you have a neutral used as a current carrying conductor, then you must use a grounded system, but there isn't a neutral at the source, so where do you bond?

If you have a three wire feeder from a _grounded_ system, and add a zig-zag transformer, then how do you treat the neutral conductor? Bonding the neutral would mean 'objectionable current flow'. Leaving this _derived_ neutral unbonded IMHO makes it a '0V phase conductor'. It is plausible to me that you could use such a derived neutral, but that you would be required to treat is as an ungrounded conductor, which would be quite expensive (4 pole panelboards, double pole switches for each load, etc.).

-Jon
 
winnie said:
But if you have a three wire feeder from an ungrounded delta, and you add a zig-zag transformer, I don't see how you could properly bond the system and use the neutral. If you have a neutral used as a current carrying conductor, then you must use a grounded system, but there isn't a neutral at the source, so where do you bond?
-Jon
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Would you not bond the GEC to the ungrounded conductor on the secondary? Primary is irrevelant.
 
As the original replies were stating, you can get 480V, 1-phase ballasts for T5HO54W lamps. These can be connected to 2 pole breaker on a 3-phase, 3-wire system. If you're adding a whole panel then you probably have lots of lights to add. Just try to ballance them a well as you can across A-B, B-C, and C-A.
 
Thanks

Thanks

I appreciate all of your responses, I was just curious what would be the best engineeried / cost effective to accomplish this. It sounds like the xfmr is the best way to go a 150Kva mounted above the panelboard, the problem with 480v ballasts is the cost of the ballasts plus the cost of the lighting control panel to control the fixtures becomes more expensive at 480v than 277. I was just curious if there was another way I remember seeing in a residential application before installed at a three way was a piece of romex from a receptacle located in the adjacent bathroom with the neutrals and gounds connected and the hot left capped at bolth ends, as it turns out they needed a neutral and borrowed it from the toilet room receptacle..
 
Mike01 said:
. . . a piece of romex from a receptacle located in the adjacent bathroom with the neutrals and gounds connected and the hot left capped at bolth ends, as it turns out they needed a neutral and borrowed it from the toilet room receptacle..
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Always, always, always a bad idea, not to mention illegal, and for good reasons, electrical as well as dangerous.
 
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