Grounding on Transformer Primary Side

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ianis

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What is the danger of not connecting a grounding wire on the primary side of a transformer?
From the main switch/breaker there is a 4wire and ground (TECK) running to the transformer. The Xo on the secondary was grounded and bonded to the frame, and the ground comming from main switch to the high side (H) was bonded to the frame.
I believe the grounding on the primary side is for protection of the primary windings or does it have any other purpose?
 
ianis said:
What is the danger of not connecting a grounding wire on the primary side of a transformer?
Click to expand...

What is the danger of not hooking the grounding wire to any electric equipment?

The NEC requires that electrical equipment be grounded and that the grounding means runs back to the source with the circuit conductors.

Basically the EGC with the primary conductors provides a ground fault path back to the source if one of the primary conductors faults to the raceway or enclosure or if the primary windings fault to the transformer enclosure.
 
ianis said:
From the main switch/breaker there is a 4wire and ground (TECK) running to the transformer.
Click to expand...

Four wire and a ground?

As in A, B, C, N and Grd?

Is this a wyw to wye transformer?

What is the primary neutral doing?

Maybe I am misunderstanding you, is this four wire and Grd on the primary or secondary side?
 
Does this drawing represent what you have?

480-208Y120_Trans_Panel.gif



Drawing courtesy of Ed MacLaren :cool:
 
As in Bob's last post showing Ed's illustration of the terminations at a transformer, a little theory should be explained.

Even though there is an equipment ground conductor connection on the secondary side, there would still need to be an EGC on the primary side.
Every electron that leaves a source wants to return to that same source.
On the primary side, the source most likely is the transformer in the street supplying the building service. If there is a fault on the primary side, that fault will flow back to that source. The fault current on the primary side will flow through the EGC on the primary side, and not the EGC on the secondary side.


I am also interested what the 4 conductors on your primary side are for.
 
when we opened the transformer we found the ground out on the primary side and also an additional wire tacked inside the transformer case. The drawing represents what we found except that on the primary side the ground and the additional wire were bent and tied around the corners of the transformers. We have tied in the ground to the frame but I am not sure what to do with the extra wire.
 
if the transformer just feed a single rack of equipment, and the equipment has their own power panel with plastic enclosure, do i need grounded X0?
 
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