trane unit

[hvac17011]

Im working on a large trane split. It has a 3 transformers.1 for od unit 1 for economizer and 1 for inline gas duct furnace. Is it ok to have all the commons tied together. I guess they all eventually go back to ground. This is a 24v setup.

[dick johnson]

Yes, as long as the polarity is the same on the primary side as well.

Mr. "Dirty" Dick Johnson

[seaboard]

If all the commons are isolated meaning that the common side is connected to earth ground then they are all tied together whether the commons are actually connected or not so long as all the equipment is properly grounded. Is this system controlled by an EMS system which separates the contacts for each device? I was performing a PM on a RTU once and touched the "R" wire and got shocked. I thought it odd and my imagination and went back for some more! Then I used my meter and found 147 volts present. The low voltage transformer was unisolated and in a building control panel downstairs the maintenance man had switched some wires hen replacing a relay and the 120 volts was "piggybacked on top of the 24 volts! The unit was running fine. So long as nothing shorted, the 24 volts operated all the contactors and the 120 volts had no path to ground...that is until I came along.

[hvac17011]

no this isnt hooked up to ems.It had one of those old enerstat stats with the abcd to program and the maint man tried to replace and had all the wires hanging there and said here.one of those deals y1 starts as yellow ends up blue. I saw they were all tied together in airhandler wasnt sure