Transformer neutrals
- Thread starter LYLE2231
- Start date
- Status
- Location
- Illinois
- Occupation
- retired electrician
No real effect. That connection exists, via the primary and secondary EGCs and the main and system bonding jumpers for almost all transformers. The connection of the primary grounded conductor to XO would be a code violation because it would result in a second point of connection for the primary grounded conductor to ground (via the system bonding jumper)
weressl
Esteemed Member
Since you are not differentiating between X0's I presume that you are refering to the wye point in the secondary windings and I further deduse that you are talking about a standard Delta/Wye trasnformer, especially since you not identified teh primary as 480/277V. There would be no reason to run a neutral to the trasnformer, nor would be any reason to land a primary source conductor on the secondary side windings.
- Location
- Illinois
- Occupation
- retired electrician
250.24(a)(5)don, what code article are you referencing?
Thanks for the help, lyle
xformer
Senior Member
- Location
- Dallas, Tx
- Occupation
- Master Electrician
If memory serves correct there is a time that the primary grounded conductor needs to be routed with the ungrounded conductors feeding a transformer.... I in the instance of grounding a secondary on a Y secondary. If memory serves correct.
xformer
Senior Member
- Location
- Dallas, Tx
- Occupation
- Master Electrician
Sorry everyone,
I was remembering trying to ground a boost transformer to achieve proper voltage for controls...
I was remembering trying to ground a boost transformer to achieve proper voltage for controls...
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
This is incase the primary is a 480/277
If you either bond the primary XO to an EGC or feed it with a supply neutral on a common core transformer and the secondary has line to neutral loads that become unbalanced (most likely will) this will cause high heating in the transformer cores and place high currents on this bond conductor, I have seen them burn off before, always feed a common core transformer line to line only and don't bond the primary XO
Otherwise Don is correct, supplying a primary neutral to the secondary XO will result in a rebonding of the grounded conductor which is not allowed in the NEC after the main bonding jumper in the service. but the secondary does have to have the XO grounded, this allows a fault current path in the event of a ungrounded circuit from this transformer coming into contact with any metal surfaces that is grounded to the supply side.
If you either bond the primary XO to an EGC or feed it with a supply neutral on a common core transformer and the secondary has line to neutral loads that become unbalanced (most likely will) this will cause high heating in the transformer cores and place high currents on this bond conductor, I have seen them burn off before, always feed a common core transformer line to line only and don't bond the primary XO
Otherwise Don is correct, supplying a primary neutral to the secondary XO will result in a rebonding of the grounded conductor which is not allowed in the NEC after the main bonding jumper in the service. but the secondary does have to have the XO grounded, this allows a fault current path in the event of a ungrounded circuit from this transformer coming into contact with any metal surfaces that is grounded to the supply side.
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