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Discussion Starter · #1 ·
I was reading a thread earlier about bonding XO in a transformer, and I asked a question about it. Not sure if I misspoke or stepped on toes, so I am going to try again. I have had some old timers show me how to wire up a transformer in the past. They always had a single primary and secondary feed. They would take the grounded conductor emerging from the secondary feed conduit and run it unbroken thru XO and then to a lug that grounded the case of the XFMR by stripping enough insulation to allow the wire to be tightened down bare in the XO lug, and leaving the remainder insulation intact until it landed on the grounding lug. There were additional XFMR case grounding lugs for the pri and sec and building steel GECs. Has anyone else seen this done? Is this an old style of wiring, completely incorrect, or what?
 

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You have not given us enough to work on !
Weather or not a transformer winding is grounded ?
and where, depends on several factors !

Type of windings
Load
supply configuration

All these things play a part !
And probably even more !

:whistling2:
 

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I have always seen the X0 have two lugs or a double lug. The neutral conductor lands on X0 and stops there at lug #1. The grounding conductor comes into the enclosure, passes through the second X0 lug unbroken, and then goes to the enclosure bonding lug. This arrangement gives the neutral an unbroken connection to the grounding electrode.

The arrangement you're describing means that the integrity of the grounding conductor depends three lugs staying tight, whereas the one I described requires only one of them to stay tight. If you're in Canada, your arrangement is illegal.

10-806 Installation of system grounding conductors (see Appendix B)
(1) The grounding conductor for a system shall be without joint or splice throughout its length, except in
the case of busbars, thermit-welded joints, compression connectors applied with a compression tool
compatible with the particular connector, or where it is necessary to control the effects of stray earth
current, devices specifically approved for connection in series with the grounding conductor.
 

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Discussion Starter · #4 ·
Sorry. 3 phase Primary 3 wire 480v delta. Secondary 208v wye. Typical commercial/light industrial install any kva feeding 120/208 lights/plugs/dedicated equip. Etc. Don't remember it being anything special. Most of the guys I remember learning this from have retired or passed.
 

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Discussion Starter · #5 · (Edited)
Vintage sounds, your response came in as I was typing my second one. I think your description is correct and my memory is a little off. Your explanation is spot on, and makes more sense. Thanks! So is this a better way to wire up a transformer?
 

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You have not given us enough to work on !
Weather or not a transformer winding is grounded ?
and where, depends on several factors !

Type of windings
Load
supply configuration

All these things play a part !
And probably even more !

:whistling2:
What's with the exclamation points? You sound like a new stepdad trying to assert your authority.
 

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Vintage sounds, your response came in as I was typing my second one. I think your description is correct and my memory is a little off. Your explanation is spot on, and makes more sense. Thanks! So is this a better way to wire up a transformer?
That is the most common way and often the easiest. In some situations I've seen compression connections instead of a single unbroken wire. You could also bond the neutral in the first disconnect on the secondary side, but I've never seen that anywhere.

10-206 Grounding connections for different systems at a facility (see Appendix B)
(1) Where, in addition to the system supplying the consumer’s service as described in Rule 10-204, one or more
different systems conforming to Rule 10-106(1) exist at a facility,
(a) each different system shall be connected to a separate grounding conductor
(i) at the transformer or other source of supply; or
(ii) at the first switch controlling the system.
I don't know if you're in Canada or the US but this is what the CEC says.
 
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