I'm feeding an existing 240V-3PH-3W panelboard via a transformer from a 208V service. I had specified a 208Y-240D transformer suitable for reverse connection, leaving X0 disconnected (per other posts on this forum). The contractor submitted a delta-delta transformer. Are there any issues with this if we don't ground the primary coils, just run the line wires and an equipment ground to the enclosure? secondary will be corner grounded delta. a diagram on the submittal sheet shows what appears to indicate H1 and X1 legs grounded. Electrically, I would think it would be okay, I just want to make sure I'm not overlooking something. Thanks,
208V-3PH PRIMARY - 240V-3PH transformer
- Thread starter DW98
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- Wisconsin
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- PE (Retired) - Power Systems
You do not need, nor probably really want, a 208Y primary connection.
For non-utility applications, the most common primary connection will be a delta, regardless of the line to line voltage.
Even if you get a 208Y primary you should not connect anything to the neutral point.
For non-utility applications, the most common primary connection will be a delta, regardless of the line to line voltage.
Even if you get a 208Y primary you should not connect anything to the neutral point.
JDBrown
Senior Member
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- California
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- Electrical Engineer
I may be sticking my foot in my mouth here, since I'm not in the field dealing with the actual labels on the transformer terminals, but the above quote has me a little worried. See, I was under the impression that X1 is one of the corners of the LV delta and H1 is the corresponding corner of the HV delta. Grounding H1 is all well and good for creating your corner-grounded delta, but if they ground X1, which is connected to one of the ungrounded conductors from your 208Y source, they will be creating a bolted L-G fault.
Unless I'm misunderstanding the terminology (which is entirely possible).
- Location
- Wisconsin
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- PE (Retired) - Power Systems
It is possible the submittal data is showing a typical transformer nameplate connection diagram, which usually includes a 'dashed line' on the H1 terminal, and another on X1 or X0. This dashed line is often mistaken for a connection to ground.
kwired
Electron manager
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- NE Nebraska
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- EC
Primary and secondary are essentially two separate electrical systems. The primary connects to the three phase conductors, doesn't matter if one of them happens to be grounded or not. The case gets connected to the equipment grounding conductor of the primary regardless of whether or not the EGC is derived from a neutral or from a grounded phase.
The secondary will either have a phase grounded or a neutral grounded depending on the configuration and application.
You mentioned you have 208 three phase primary and 240 volt secondary. To have 208 primary it will have to come from a wye system which will have a neutral, which the neutral is going to be grounded in almost every case. Only connection of this primary neutral is to the case as an equipment grounding conductor.
Secondary depends on if you have a neutral or not. If no neutral then ground a phase (any one of them will work). If there is a neutral then ground the neutral.(If there is a neutral your secondary will have two 120 volt to neutral phases and a high leg that is 208 to this neutral) There is also an option of going ungrounded on the secondary, but you must have ground fault monitoring/indicating equipment when going that route.
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