Use 277v circuit for 208-230v fan-coil

[tom@teesi.com]

Seeking a transformer for 300w (0.3 kVA) 208-230v fan-coil unit so that it can be used on an existing 277V circuit. About 75 units thus.

I looked at Thread: 277 single phase single pole to, 208-230 single phase 2 pole , but that post seems to assume that the equipment has an allowed terminal voltage to ground of at least 230V. Some equipment is only insulated/spaced for 150V to ground.

It seems better to use a 2-winding transformer with a grounded center tap in the secondary winding to place ground midway between the two current-carrying conductors. Thus, both wires are under 150V to ground.

Please suggest where to find small transformers that have 277V primary and taps for 208-230v secondary with center tap.

Thomas R. Glass, PE
Austin, TX

 

[kwired]

Any other loads on these existing 277 volt circuits?

300VA x 75 units is 22.5 kVA. Seems you would be better off putting in a single larger transformer and convert existing circuits to 208 or 240 volts if there is nothing else that needs 277 V.

Not saying you can't find 277 volt primary units but they probably will be special order and come with a special price tag also.

 

[peter d]

Just use a bunch of resistors until you get to 240 volts.

 

[kwired]

Just use a bunch of resistors until you get to 240 volts.

Presuming fan coils are for heating/cooling - will lessen heating load from primary heat source, but will be a hurdle for cooling equipment.

 

[sameguy]

PH75MGJ
Not sure what your doing, but that's like a $50 control xfmr.

 

[drcampbell]

Is it possible to specify 277-volt motors in the fan-coil units?
(let me guess: They were already ordered, delivered and installed before anybody noticed that they're incompatible?)

 

[kwired]

PH75MGJ
Not sure what your doing, but that's like a $50 control xfmr.

times 75 units is 3750.

25 kVA single phase transformer is maybe only around $1000.

But we don't know what else may need to be done to install that way either.

 

[Jraef]

Seeking a transformer for 300w (0.3 kVA) 208-230v fan-coil unit so that it can be used on an existing 277V circuit. About 75 units thus.

I looked at Thread: 277 single phase single pole to, 208-230 single phase 2 pole , but that post seems to assume that the equipment has an allowed terminal voltage to ground of at least 230V. Some equipment is only insulated/spaced for 150V to ground.

It seems better to use a 2-winding transformer with a grounded center tap in the secondary winding to place ground midway between the two current-carrying conductors. Thus, both wires are under 150V to ground.

Please suggest where to find small transformers that have 277V primary and taps for 208-230v secondary with center tap.

Thomas R. Glass, PE
Austin, TX

Are you sure that you have EQUIPMENT that is only looking for 120V to ground? That can apply to things like circuit breakers, but I've never seen it related to equipment like a fan/coil unit. Because the simplest solution is to use a 100VA 120/240 to 24/48 bell transformer wired to buck from 277-231V as below:

The 100VA BB autotransformer connection will get you 580VA capacity, more than you need for this.