277/480V 200A supply stepped down to 120/240V...

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Electron manager
NE Nebraska

IIRC you did say his current 200 amp 240 volt system was about at it's limits, but that likely includes lighting, office spaces, HVAC, etc. that may already be supplied at this new location that has 480 volts. So what I'm getting at is when he moves his specialty equipment to the new site he is not necessarily moving everything that was loading the 200 amp service at the old site and putting it on this new transformer, just the specialty equipment that was brought in.


Senior Member
one would think this building has a existing 240/120 service or already has a transformer for the 240/120 loads? most 480 volt services this small I have ever run into was an added service where the building already had a single phase 240/120 volt service, so if the equipment can not be converted to 480 which most German manufactured printing presses wont have this option, just sizing a transformer to what equipment he already has and then run the rest off the existing 240/120 volt service unless its too small, but then he has the option of also installing a smaller 240/120 volt transformer to cover the needs for any loads that exceed the existing 240/120 service, the only problem is if this building already has a transformer off the 480 to feed the existing 240/120 volt loads then this has to be added to the existing 480 service.

Here are some facts, installing a transformer sized for the max now will lead to much higher electric bills for the extra wattage that the transformer will use because it is not fully loaded, your better off only installing what you need now and maybe enough to cover what is planed in the very near future, then down the road you can always add transformers as the load and equipment expands.

This is why it is always better to put the transformers on the utility side of the meter, but in existing cases then just install what is needed and add as they expand.

Also if you do decide to go with a 4-wire delta 240/120 then install a single phase panel fed from A and C phases then install a 3-phase panel only for the 3-phase loads this removes the risk of someone landing a 120 volt load on the B phase.
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