Switchboard Neutral

[dasarmin]

Our 480V Switchboards have a Neutral Bus which is wired to the X0 of a 3-phase transformer. Generally, we don’t use this Switchboard Neutral, opting instead to set transformers (480 : 480/277V) (delta / wye) as needed.
Is there an advantage / disadvantage to using a Switchboard Neutral opposed to using transformers to provide this Neutral?

 

[Tony S]

You’re in the same situation as a UK 550V board. The star point is bought out to provide ground reference and fault return path, it’s has no other use. Some boards once the transformer star point was solidly grounded I’d take all the superfluous neutral bars out, they just got in the way.

Like you, we used 550/230/115V transformers as and when needed.

I will add, if there’s more than one transformer feeding the board the “neutral” must be maintained between them.

 

[don_resqcapt19]

Our 480V Switchboards have a Neutral Bus which is wired to the X0 of a 3-phase transformer. Generally, we don’t use this Switchboard Neutral, opting instead to set transformers (480 : 480/277V) (delta / wye) as needed.
Is there an advantage / disadvantage to using a Switchboard Neutral opposed to using transformers to provide this Neutral?

If you already have a grounded wye, and if the conductor between XO and the switchboard is large enough, why would you want to install additional transformers to get a neutral? You are adding both installation and operational costs.

 

[ron]

If you already have a grounded wye, and if the conductor between XO and the switchboard is large enough, why would you want to install additional transformers to get a neutral? You are adding both installation and operational costs.

Generally I agree on that situation, but if you get involved with ATS's downstream, the 480-480/277V transformer makes it a lot easier to digest for most.

 

[augie47]

Our 480V Switchboards have a Neutral Bus which is wired to the X0 of a 3-phase transformer. Generally, we don’t use this Switchboard Neutral, opting instead to set transformers (480 : 480/277V) (delta / wye) as needed.
Is there an advantage / disadvantage to using a Switchboard Neutral opposed to using transformers to provide this Neutral?

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The only time I have seen this done in order to gain an "advantage" was as a method to reduce fault current. I have inspected a few jobs with very high ampere services and high available fault current where the engineers used 480 to 480/277 transformers simply to reduce SCA at the lighting panel-boards located close to the service gear..

 

[dasarmin]

Generally I agree on that situation, but if you get involved with ATS's downstream, the 480-480/277V transformer makes it a lot easier to digest for most.

The X0 connection to the Switchboard is a legacy thing I guess, all our transformer / distributions are wired this way.
The policy here has been not to use this Neutral Bus in the SB, which in most cases makes sense. We don't have a lot of Neutral required loads, mainly lighting and 208/120V Loadcenters. We set transformers for these, usually 90kva or less, so the expense of pulling a Neutral from the SB wouldn't make sense.
We have new systems going in that will require Neutral for 277Vac heat circuits. These will all be fed from (1) SB, so we thought instead of setting a transformer (approximately 225kva) for each, why not use the Neutral from the SB.
Valid question, I think at the end of the day; a cost analysis will tell the tale. Is the additional Neutral cable and associated expense less than a transformer and associated wiring. There are also a few questions within the SB, since the main and feeder CBs will be monitoring the Neutral Bus via a CT. The feeder CBs don't worry me, with the right coordination, just want to be sure not to trip the main.