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Old 03-02-2019, 01:40 AM   #1
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I recently found out on a transformer even one you mount in a box? 347 to 120 you need to ground one leg of the 120 volt side. Can someone explain?
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Old 03-02-2019, 05:46 AM   #2
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Originally Posted by Bigbilly View Post
I recently found out on a transformer even one you mount in a box? 347 to 120 you need to ground one leg of the 120 volt side. Can someone explain?
So that there is a complete circuit path for current to flow if there is a ground fault downstream.
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Old 03-02-2019, 07:33 AM   #3
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The transformer secondary needs the "neutral" grounded so the over current protection will work on a short to ground on the "hot" secondary conductor(s).

Grounding the "neutral" also makes searching for problems much easier, as you can check voltage, from the energized conductors, to any available ground.
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Old 03-02-2019, 09:30 AM   #4
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I recently found out on a transformer even one you mount in a box? 347 to 120 you need to ground one leg of the 120 volt side. Can someone explain?
Assuming your in Canada with the 347 volts, yes you must ground the secondary. Even if the secondary is lower than 50 volts, if the primary is over 150 volts to ground you must ground it.
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Old 03-02-2019, 09:35 AM   #5
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Originally Posted by varmit View Post
The transformer secondary needs
a grounded conductor (most often the neutral) so the over current protection will work on a short to ground on the "hot" secondary conductor(s).

Grounding a conductor also makes searching for problems much easier, as you can check voltage, from the energized conductors to any available ground.
Fixed it for you.
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Old 03-02-2019, 02:37 PM   #6
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Electric circuit 600Y347 (primary windings )
Magnetic circuit ( the flux inside the three-phase transformer )
Electric circuit 208Y120 (secondary windings )

Until you've grounded the secondary winding circuit it is ELECTRICALLY isolated -- via the magnetic circuit. Re-stated, it has no point of reference. This means that -- until it's grounded -- the secondary is an un-grounded system.

Check out the threads on un-grounded Services. They are 'floaters.'

( 600 3-phase or 480 3-phase -- it makes little difference diagnostically. )

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Old 03-02-2019, 08:24 PM   #7
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Old 03-02-2019, 09:13 PM   #8
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Fixed it for you.
Old habits are difficult to change.
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Old 03-02-2019, 09:34 PM   #9
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Assuming your in Canada with the 347 volts, yes you must ground the secondary. Even if the secondary is lower than 50 volts, if the primary is over 150 volts to ground you must ground it.
Does the CEC differentiate between a grounded & a grounding conductor?
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Old 03-02-2019, 09:52 PM   #10
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Does the CEC differentiate between a grounded & a grounding conductor?
Yes.
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Old 03-04-2019, 12:47 PM   #11
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Assuming your in Canada with the 347 volts, yes you must ground the secondary. Even if the secondary is lower than 50 volts, if the primary is over 150 volts to ground you must ground it.
good to know i've seen some 600--24v xfmer install and the 24v was floating
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Old 03-04-2019, 01:14 PM   #12
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good to know i've seen some 600--24v xfmer install and the 24v was floating
Also, depending on the voltage and va, you might have to fuse the secondary.

16-104 for class 1 transformers
16-200 for class 2
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