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Old 07-10-2013, 05:46 PM   #1
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Default Bonding neutral at transformer

I have a 7.5 kva 480 volt single phase primary and120volt secondary .The transformer says to combine x1 and x3 , and x2 to x4 for 120volt . There was no bonding from neutral to ground , or grounding for secondary installed . (i plan on repairing that ) My question is could that in some way contribute to slight overheating of the transformer or possible voltage irregularities. the transformer seems to be slightly hotter to touch then normal .someone put in a raintight transformer inside and it has NO venting I thought that could also be a contributing factor to the slight overheating

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Old 07-10-2013, 05:49 PM   #2
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Bond X1 and X3 to ground. That will be your neutral.

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Old 07-10-2013, 05:49 PM   #3
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The lack of bonding would cause odd voltage reading line to ground but would not change the readings line to line.

It sounds like an encapsulated transformer and those get very hot to the touch.

Read the tag on it and see how many degrees of rise it is rated for, likely you will be surprised how hot the label allows.
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Old 07-10-2013, 06:05 PM   #4
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Its rated for 180 degrees ,its only a single pole 120 volt ckt .i didnt have time to take voltage readings before end of shift but i opened it and noticed the missing bonding and grounding and thought that could contribute . a operater at the plant touched it and thought it was overheating but you made a good point if its rated for 180 degrees its a poor choice of transformer for the location it was installed.and i plan on making that neutral a actual "grounded" conductor tonight
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Old 07-10-2013, 07:12 PM   #5
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are you sure it's X 1 X 3, and does it matter which one you bond. I planned on taking voltage reading to see if I can distinguish which one would be a neutral
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Old 07-10-2013, 07:22 PM   #6
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are you sure it's X 1 X 3, and does it matter which one you bond. I planned on taking voltage reading to see if I can distinguish which one would be a neutral
It does not matter which one you bond. Until you make the bond there is no grounded conductor. Voltage readings will not really tell you anything other than it is an ungrounded system.
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Old 07-17-2013, 07:54 AM   #7
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Quote:
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the transformer seems to be slightly hotter to touch then normal .someone put in a raintight transformer inside and it has NO venting I thought that could also be a contributing factor to the slight overheating
No venting, or totally enclosed does not necessarily mean raintight. There are plenty of ventilated NEMA 3R transformers.
Is there alot of dust, or lint/powders in that area?
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Old 07-17-2013, 02:26 PM   #8
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its a poor choice of transformer for the location it was installed
How did you come to this incorrect conclusion?
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Old 10-06-2013, 12:57 AM   #9
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Yeah typically those smaller encased transformers you can fry eggs on even under very little load.

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