jake21
Member
- Location
- North Carolina
Hi All, I have a 75KVA 480-240/120 center tapped transformer. Do I need to have 4 Wire panel at its downstream where center tap will act as a neutral?
Thanks
Thanks
Downstream Panel selection for 480-240/120 center tapped transformer
- Thread starter jake21
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kwired
Electron manager
- Location
- NE Nebraska
AFAIK you need to bring the grounded conductor to the first disconnecting means.
After that if the load served doesn't utilize the neutral conductor you do not need to bring a neutral conductor to it.
You do need equipment grounding conductors to pretty much everything regardless, but the EGC separates from the grounded conductor at the system bonding jumper location. That bonding jumper location is permitted at either the first disconnecting means or to the transformer case.
If you bond at the transformer you need separate EGC and neutral to the first disconnect.
If you bond at the first disconnect you need to run an EGC back to bond the transformer case.
Either way you need 4 wires between transformer and first disconnect - unless you use a raceway that qualifies as an EGC.
You can bond both the transformer and first disconnect if there are no metallic paths between the two.
After that if the load served doesn't utilize the neutral conductor you do not need to bring a neutral conductor to it.
You do need equipment grounding conductors to pretty much everything regardless, but the EGC separates from the grounded conductor at the system bonding jumper location. That bonding jumper location is permitted at either the first disconnecting means or to the transformer case.
If you bond at the transformer you need separate EGC and neutral to the first disconnect.
If you bond at the first disconnect you need to run an EGC back to bond the transformer case.
Either way you need 4 wires between transformer and first disconnect - unless you use a raceway that qualifies as an EGC.
You can bond both the transformer and first disconnect if there are no metallic paths between the two.
Required for service but not for separately derived system.... which of course means there will be no line-to-neutral loads.
The center tap is typically required to be grounded (depending on loads) whether neutral is run or not. System bonding jumper and GEC can be connected at first disconnecting means if the neutral is run.
jake21
Member
- Location
- North Carolina
I have 3-phase, 240V load only. Can i just ignore the center tap and just use 3 wires on secondary like a delta only?
I just wanted to have an option for feeding 120V, single phase loads in future from the same transformer. Can i do that using the center tap of the transformer?
I just wanted to have an option for feeding 120V, single phase loads in future from the same transformer. Can i do that using the center tap of the transformer?
- Location
- Massachusetts
Sure but how are you bonding it to ground .... Or are you going ungrounded delta with ground fault indicators?
kwired
Electron manager
- Location
- NE Nebraska
You have to bring a grounded conductor to first disconnect, whether it be a neutral conductor or a grounded phase conductor, or is just used as an equipment grounding conductor. If EGC only it can be qualifying metal raceway, cable sheath or other wiring method, plus EGC still needs extended (wiring method again acceptable) to nearly everywhere in the system.
I don't have a problem with using a transformer with an X0 (I think on this kind of system it is more typical for it to be labeled X4) terminal as a corner grounded or ungrounded system - just make sure to not connect anything to X0 (X4). Listing and instructions may tell you differently though so keep that in mind as well.
If building a three phase delta out of separate single phase transformers - you have to leave two of the center taps unused or at least can not connect them directly together in any way if you are building some unusual supply, or you will create a short circuit, and if building a corner ground or ungrounded system you have to leave all three center taps unused.
Grounded does not equal grounding.
kwired
Electron manager
- Location
- NE Nebraska
I know, should have worded it differently. He still needs a conductor where he is asking about - unless the wiring method itself is a qualifying EGC. If he has 120 volt loads to supply he needs two conductors (most instances) where he is asking about.
That is the short but less technical version.
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