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Old 06-07-2012, 10:35 PM   #1
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Gfi tripping on 900w low voltage xfmr


I have a 900W low voltage transformer for outddor lighting. The load which is broken up on 3 output legs adds to a total of 650W (13 x 50W bulbs). My 20 amp breaker does not trip but my GFI outlet which feeds the transformer keeps tripping. I have changed the GFI outlet and installes another which has 2 115Vac outlets. I have run an extension cord from the new GFI outlet to the 900W transformer and sometimes the lighting holds for a half hour and then the GFI trips. I have even changed all the 50W bublbs and it still trips. Any help or ideas would be greatly appreciated.
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Bob Folmsbee

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Old 06-07-2012, 11:04 PM   #2
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Gfi tripping on 900w low voltage xfmr


Could be moisture in the 900watt xfmr box or worse insulation breakdown of windings. Can you plug 900w via extension cord to a different gfci, say in garage just as a test to see if it stays up. If it works off of a different gfci then it points to wiring from original gfci to xfmr or other items on load side of that gfci. If a different gfci trips then your xfmr is probably toast. I wouldn't worry about 12vdc side of things much. Gfci can't detect a ground fault on other side of xfmr. That circuit is isolated by the transformer core.

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Old 06-07-2012, 11:14 PM   #3
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Gfi tripping on 900w low voltage xfmr


Will try tommorow- great idea-thanks!
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Old 06-08-2012, 07:08 AM   #4
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Gfi tripping on 900w low voltage xfmr


The issue is in the transformer, as a side note, the GFCI protection does not precede past the windings in the transformer, so the load side of a transformer is NOT gfci protected....
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Old 06-08-2012, 08:37 AM   #5
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Gfi tripping on 900w low voltage xfmr


Thanks, load appears to be holding so far over an hour being fed from another GCFI outlet. Will monitor if holds for the day with rain coming I plan to disconnect the UFC cable to the transformer from faulting GFCI and try using the outlet again. Thanks guys! Knowing the transformers low voltage side is not a cause for the tripping GFCI circuit was a big key!
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Old 06-08-2012, 10:01 AM   #6
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Gfi tripping on 900w low voltage xfmr


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Originally Posted by BOBFOLMSBEE View Post
Thanks, load appears to be holding so far over an hour being fed from another GCFI outlet. Will monitor if holds for the day with rain coming I plan to disconnect the UFC cable to the transformer from faulting GFCI and try using the outlet again. Thanks guys! Knowing the transformers low voltage side is not a cause for the tripping GFCI circuit was a big key!
maybe check load side of the problem GFCI. Maybe it is some down stream receptacles that are wet causing the GFCI to trip and it might not be xfmr at all..
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Old 06-08-2012, 03:20 PM   #7
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Gfi tripping on 900w low voltage xfmr


Thanks to all. Problem isolated to UFC wire between GFI outlet and xfmr. Disconnected UFC wire and ran extension from GFI outlet to xfmr and GFI not tripping under load and in the rain. Thanks again to all!

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