I was contracted by a local mechanical contractor to bring power to a 125 amp libert ac unit at 480 volts . They made a mistake and ordered a 208/240 at 155.5 amps unit at a coast of 50,000 returning it is not an option . SO I set a 45k 208 volt transformer. on start up the ac is at 211 volts (nice) however the commissioning of the unit requires the ac and DE humidifier and heating element to run at the same time as the ac this is causing the voltage to drop to 198volts He still has more items that need powered at the same time and my fear is he will lose even more voltage..
Any suggestions before i get back to this guy Monday morning .
Liebert field guys can be a lot sharper than normal and that's usually a good thing. Anything out of spec I would expect to get escalated to the office engineers directly.
Depending on the application it is possible for the AC to run in dehumidification mode and then reheat is necessary to balance the space temp. I've seen it, heat and AC on at the same time, especially with bad control system setup. It could also be a useable feature of the system or a design requirement for the application. Like driving your car in the rain, run the AC and heat at the same time for dry heat.
Needs a load calc with the heat and AC both on to see if the feeder and tranny are big enough for continuous loading. If the feeder or the tranny fail the load calc .. You would need the application requirements, does heat and AC have the option of running at the same time or are they mutually exclusive.
Second, the Liebert units dual voltage 208/240 rating, sometimes the only change to the unit is a tap at the control transformer for 208/230, nothing else. If that is the case you may be able to set the distribution transformer taps higher. Taps are usually every 2.5% so you may be able to get 5% or 10% higher system voltage going to the higher taps.