Heating, Air Conditioning, Fridge, HVAC/Transformer Wiring


I have a new multi tap transformer, 120/208/240vac step down to 24vac out.  My HVAC system has 2 120vac legs coming into a circuit breaker and then both 120vac legs go to their appropriate places.  The old transformer had 2 primary side 1/4" connectors.  Easy, put one each 120vac leg on each 1/4" connector.  The new transformer has 4 primary side wires white-com, black-120, red-208 and orange-240.  My question: Where do connect the 2 120vac legs to the transformer?  Which leg to which colored wire?

Your system runs on a 208-240 volts circuit.  The actual voltage varies from place to place.  You must measure, with a meter, across the wires coming into the unit to determine what your actual working voltage is.  Then use the white for one wire.  The second is important because you need to pick the closest of the two red or orange.  That then determines the secondary voltage.  If the secondary voltage is too high or low it could cause the system to fail.


Heating, Air Conditioning, Fridge, HVAC

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Craig HVAC Expert


I have been in the HVAC field for the past 18 years. I can help with most HVAC questions. I work on commerical buildings for the most part, and have yet to find anything I could not troubleshoot and repair, when repairable. I work on small 1 ton units to a 2500 ton chiller. Troubleshoot air flow, elect, and control problems. I attend regular classes to keep up with the latest and greatest.


I work on commerical sites, hospitals, gov't buildings. I can troubleshoot just about anything in the HVAC business.

5 years trade school, VFD training classes, Liebert factory training, some York and Trane factory training.

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