XFMR primary phasing Question

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martsco11

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I repaired a conduit the other day with 3 phase 480v feeding a 30KVA xfmr (120/208v). Although I did not have to open the xfmr or panel to make the repairs, the colors of all three #8 wires (primary) were black. The ground wire (#10) was easy enough to depict. After the U/G repairs, I terminated the wiring, energized the system, and found all voltages proper to neutral, ground and phase to phase. A co-worker mentioned I should of properly phased the primary to the XFMR. I retorted "The XFMR is not a motor, therefore phasing is just good practice, not a necessity." H1 brown H2 Orange H3 yellow. Question: Will this actually have an affect on the life of the XFMR if I accidently put the "C" phase wire (yellow) to H1 or H2, and why? No motors, or 3 pole breakers on the secondary side.
 
martsco11 said:
I repaired a conduit the other day with 3 phase 480v feeding a 30KVA xfmr (120/208v). Although I did not have to open the xfmr or panel to make the repairs, the colors of all three #8 wires (primary) were black. The ground wire (#10) was easy enough to depict. After the U/G repairs, I terminated the wiring, energized the system, and found all voltages proper to neutral, ground and phase to phase. A co-worker mentioned I should of properly phased the primary to the XFMR. I retorted "The XFMR is not a motor, therefore phasing is just good practice, not a necessity." H1 brown H2 Orange H3 yellow. Question: Will this actually have an affect on the life of the XFMR if I accidently put the "C" phase wire (yellow) to H1 or H2, and why? No motors, or 3 pole breakers on the secondary side.
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It will not have any effect on the performance of the transformer.
If there had been any phase sensitive three phase loads on the secondary it would have had a very big effect.
If there was phase identification on the secondary wires or in the panel, and you changed the phase rotation it could have effects later if three phase equipment were added.
 
martsco11 said:
I repaired a conduit the other day with 3 phase 480v feeding a 30KVA xfmr (120/208v). Although I did not have to open the xfmr or panel to make the repairs, the colors of all three #8 wires (primary) were black. The ground wire (#10) was easy enough to depict. After the U/G repairs, I terminated the wiring, energized the system, and found all voltages proper to neutral, ground and phase to phase. A co-worker mentioned I should of properly phased the primary to the XFMR. I retorted "The XFMR is not a motor, therefore phasing is just good practice, not a necessity." H1 brown H2 Orange H3 yellow. Question: Will this actually have an affect on the life of the XFMR if I accidently put the "C" phase wire (yellow) to H1 or H2, and why? No motors, or 3 pole breakers on the secondary side.
Click to expand...


Then it doesn't really matter.
 
Thank you gentlemen. I have been at this a long time and, as good practice I have always terminated the wiring in phase sequence when installing transformers. This was a unique situation, so I did my due diligence by making sure there weren't any 3 phase 208v breakers in the secondary panel. My Co workers argument was "why then do manufacturers put "h1, h2, h3" labels on their termination blocks? " I hope I'm not wrong by telling him " possibly for warranty issues, or possibly for people like him who are looking for a way to be right".
 
If they put H7, H43 and H672, people would be confused.

Phasing is always relative. It makes no difference in theory. That said, SOMETIMES there are naturally occurring very slight differences in equipment construction, including transformers, that can result in minor variances in voltage balance. Those differences in transformers in series can amplify those balances, but also correct the variances in each other. So if you have a connection sequence that resulted in a well balanced system, then reconnect it in a different orientation, you may end up with an increased imbalance. All you do is "roll" the phases however. I always do that first if I see an imbalance, is the cheapest easiest thing to try first.
 
It would make a huge difference if you had a high leg system and energized the A or C legs with 208V instead of 120V. Otherwise, no problem unless you had 3ph motor loads, which you checked for.
 
martsco11 said:
Thank you gentlemen. I have been at this a long time and, as good practice I have always terminated the wiring in phase sequence when installing transformers. This was a unique situation, so I did my due diligence by making sure there weren't any 3 phase 208v breakers in the secondary panel. My Co workers argument was "why then do manufacturers put "h1, h2, h3" labels on their termination blocks? " I hope I'm not wrong by telling him " possibly for warranty issues, or possibly for people like him who are looking for a way to be right".
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Because if there were loads that were impacted by rotation it might matter more, your instance it did not matter.
 
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