Bringing 3-phase 120/208V service to existing 1-phase 120/240V facility

[katwalatapan]

Hello,

An existing 2-storey multi-unit residential facility built in 1980 has 400A, 1-phase, 120/240V electrical service. It is intended to upgrade the existing service to 3-phase, 120/208V, 600A, electrical service, to accommodate an addition of new 3-phase, 208V elevator in the building.

I understand, that we may need to verify if any existing high-energy, 1-phase equipment such as air handling units, HRVs, cloth dryers, kitchen range, etc., are compatible with 208V with a 208/240V listing, prior to considering the upgrade. Is it practical to install a 208V to 120/240V buck boost transformer to make the electrical service compatible with the existing 240V equipment?

Some equipment may take time to work upto intended standards, such as the kitchen range may take longer to heat up or cloth dryer may take longer to dry clothes, etc. But my concern is the damage to the equipment and general safety of using a 208V service to serve loads rated for 240V.

I'd appreciate your comments on the above issue.

Thank you.

 

[jraef]

As a general rule, 240V single phase equipment small enough to be in a residential unit will be fine with 208V, the motor industry generally makes motors 5HP and under as dual rated, showing a higher FLA at 208V than at 230V on the nameplate. Anything with resistance heating will be as you say; slightly lower heat output, but most homeowners will not notice. Most other residential appliances, such as the dryer, will use 120V motors. The only possible exception will be air conditioning compressors or heat pumps. Most of the ones I have seen will be fine with 208V. But if you want certainty, someone will have to do the physical inspection and if the AC mfr will not support a 208V input, you will have to install a boost transformer. I would not boost the entire facility, because that will make your 120V circuits into 138V and cause more problems there. So you would get a BB transformer for each individual AC unit as needed, and ONLY service the motors that need it directly.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[itsmoked]

If the air conditioning was put in as 240VAC then you should boost the compressors back to 240V. They are the one thing that will care greatly and while they will probably continue to work for a while they will likely fail soon on 208V. Even the ones labeled 208/240 are mostly relabeled for marketing not reality. Ones just a couple of years old may be OK but more than about 3 years and you're asking for it.

Why don't you just add a standard wild-leg to support only the elevator instead of slowing everyone's water heaters, ovens, and stoves down?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[MatthewDB]

Most utilities won't do a new service for high leg delta. Particularly so if it is underground primary. High leg delta is prone to blowing fuses on a phase loss and ferroresonance. The ferroresonance is particularly troublesome for underground primary.

 

[Compositepro]

With a high leg delta you can only use one of the three phases to power the single phase loads. The other phases do not have a grounded center tap. So you basically still have the original single phase service.

 

[katwalatapan]

Thank you very much for your inputs on this issue.