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	Subject - transformer heat eleccon I have a 480/Y to 240 transformer that I only need single phase 240 from. My question is, will the transformer heat up if you only draw a single phase load from it? and where can I find wiring diagrams to look at since I do mostly residential and light commercial? eleccon Well I did it and it did not heat up. I balanced the loads the best I could and it has been running for a couple of days with no heat. I am puzzled by two other things though, It is a 408/277Y primary and I get 240 delta off of the secondary. I thought a wye transformer would have a wye secondary and a delta transformer would have a delta secondary. Also when I use 120 volt for some GFI's, the receptacle trips by the button but not by grounding it with a tester. eleccon OK, here is what I found out: the transformer will convert wye to delta and I will only get 1/3 of the kva by tapping it single phase. I also found out my GFI problem: You need to tie the neutral and grounds together at the source, which is the transformer or the panel. I am only posting my progress to hopefully help somebody with similar questions in the future. lctrc789 eleccon, their are Delta to Delta transformers as well as WYE to Wye and even Wye to delta and Delte to Wye. And 3 Phase does lose some of its KVA rating when you use only single phase loads. Grounding the transformers is very important a transformer doesn't know what ground is unless you tell it so to speak.. X/0 and the grounds should be tied together as well as the casing and grounded to steel, water ground, building steel etc.. You could take a transformer and ground SAY C phase and have voltage phase to phase but no voltage present at the C phase to ground and it would work. Hope this makes sense to you PEI Get a hold of your nearest Sq-D rep (or other reputable XF mfg.) You are only supposed to use about 5% of your KVA rating for 120 volt applications - and that ain't much. As long as you are lightly loading your XF at 240V it should last but, if you are heavily loaded, the end is near. For your grounding, you will notice that you are to wire the leg of one phase with orange wire, and your line-to-line phase opposite that will have your 240 volt line-to-line voltage broke down to a center tap to get your 120 volt output. The reason for the orange wire is to denote that your secondary voltage from that leg to ground is not going to be the expected 240 volts - it is across 1-1/2 phases, not one. In the Sq-D catalog, they note "connect B-phase to X3 to meet NEC 408.3". I also believe that you are to special label this transformer, but I can't remember the proper wording. eleccon Okay. my transformer is lightly loaded but I'm not understanding why to mark one phase orange and I did mark the transformer as to power in and power out.