Transformer neutrals

Status
Not open for further replies.
L

LYLE2231

Member
Friends, Given a tfmr 480 volt primary / 120/208 volt secondary. If you connect a neutral from the primary source to XO and the neutral from the secondary (load) to XO what effect would it have on the circuit?
 
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)
 
LYLE2231 said:
Friends, Given a tfmr 480 volt primary / 120/208 volt secondary. If you connect a neutral from the primary source to XO and the neutral from the secondary (load) to XO what effect would it have on the circuit?
Click to expand...
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.
 
Lyle
Are you just curious because you would not need to do this or want to do this
as per the other posts.
 
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.
 
Sorry everyone,
I was remembering trying to ground a boost transformer to achieve proper voltage for controls... :)
 
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.
 
Last edited:
Status
Not open for further replies.
Top