I like to phase my transfomrers with red dots on each winding.
I first choose one of the low voltage lugs and put a red dot on it (finger nail polish.) If I have two or three identical transformers, I also place a red dot on similar lugs in similar positions on their respective LV terminal lugs.
Now to phase them properly.
I next hook two transformers with the red dots together on the low voltage side and hook this junction to the hot of the line cord. The umarked lugs are likewise tied together and go to neutral.
I now connect any ONE of the two HV terminals on a transformer to any other HV terminal on the opposite transformer as if connecting is series. this leaves two HV leads remaining, one on each transformer.
I hook the line cord into a variac and place a good HV AC meter across the two HV leads of the pair, (hopefully, now wired in series.) If, when I bring the variac up to ten volts, the voltage really heads sky high then all is wired properly. I now place a red dot on ONE of the secondary lugs of either transformer going to the meter, it doesn't matter which. I now place another read dot on the OTHER transformer's lug which is connected between transformers. They are now phased.
If the meter in the above experiment does not leap up in voltage as the variac is advanced, then red dots go on each separate transformer HV lugs that connect to either side of the meter.
Re-connecting the HV lugs, red dot to non-red dot, and having a red dot and a non-red dot going to the meter should now see the voltage rise.
They are now phased.
After doing this for a number of transformers, it is easy to parallel or series transformers as needed using the red dots as phasing marks.
Be aware that neon transformer cannot readily or safely be series connected well, due to the grounding required of the cores and that only paralleling of the units work.
Regular isolated transformers can be series connected, but you may run into problems with insulation break down to the cores which can arc to the primaries if left floating in tranformer chains of more than three.
Richard Hull
Created on Tuesday, May 29, 2001 12:11 AM EDT by Richard Hull