2 Phase Roof Top Units?

[Bazooka Joe]

Presently an HVAC Contractor, I remember many years ago I was involved with removing 5 ton RTU that where not single or three phase. I believe the electrician called them two phase units. I vaguely remember they had to run another wire from the main distribution center to hook up to the new 3 phase RTUs. Can someone here explain how they where wired, how many line voltage wires where needed. Did those types of system use a 2 pole contactors for the compressor, or a standard 3 pole contactor. What was the common voltage used for those type of units.

[lkapigian]

All be darned

https://en.wikipedia.org/wiki/Two-phase_electric_power

[Bazooka Joe]

All be darned

https://en.wikipedia.org/wiki/Two-phase_electric_power

" This type of service happens to exist in Hartford, Connecticut. It does serve a few buildings in that city."

Thank you for the general info on two phase , Interesting, that the info you sent me mentioned Hartford CT. as still being used in a small area of town, as those RTU where located in that general vicinity. Hopefully some old timer electrician here can fill me in on the details. I vaguely remember they where Carriers with possibly Carlyle semi hermetic compressor.

Kind of makes me wonder what type of power was feeding Dunham-Bush factory, as it was based in Hartford Ct. years ago, single,two, and three phase?

[Core_d]

The two wires are out of phase... Not a mirrored sine

[Poodle Head Mikey]

Two phase was fairly common in some places. All of it that I ever worked on required four wires.

I saw lots of those Carrier water-cooled self-contained units which were two phase but never a RTU.

Where was this job you remember?

PHM
--------

Presently an HVAC Contractor, I remember many years ago I was involved with removing 5 ton RTU that where not single or three phase. I believe the electrician called them two phase units. I vaguely remember they had to run another wire from the main distribution center to hook up to the new 3 phase RTUs. Can someone here explain how they where wired, how many line voltage wires where needed. Did those types of system use a 2 pole contactors for the compressor, or a standard 3 pole contactor. What was the common voltage used for those type of units.

[Bazooka Joe]

Two phase was fairly common in some places. All of it that I ever worked on required four wires.

I saw lots of those Carrier water-cooled self-contained units which were two phase but never a RTU.

Where was this job you remember?

PHM
--------

Post #3 mentions where the units where located, apparently they are still around in a very few buildings in Hartford Ct. and more so in Philly PA.

" There remains, however, a two-phase commercial distribution system in Philadelphia, Pennsylvania; many buildings in Center City are permanently wired for two-phase[citation needed] and PECO (the local electric utility company) has continued the service. This type of service happens to exist in Hartford, Connecticut. It does serve a few buildings in that city."

OK, if you worked on it and it used four wires ,then they pulled one line voltage wire out instead of adding one wire, ( as I mentioned ) as the new replacement RTU's where three phase. That time frame was in the later 70's . Did they use four pole contactors For the compressor ? What phase where the blower motors and outdoor motor, can you get single phase from two phase to run those motors?

[Poodle Head Mikey]

Philadelphia is where I saw it. Around D and Erie Streets. It's not everywhere in the city - but I know it was there. We would just have the compressors and motors rebuilt as they failed. As manufacturing closed up out there there was lots of two-phase shop equipment available for dirt cheap. Welders, machine shop equipment, etc. Of course it was all useless anywhere else. <g>

PHM
-------

Post #3 mentions where the units where located, apparently they are still around in a very few buildings in Hartford Ct. and Philly PA.

There remains, however, a two-phase commercial distribution system in Philadelphia, Pennsylvania; many buildings in Center City are permanently wired for two-phase[citation needed] and PECO (the local electric utility company) has continued the service. This type of service happens to exist in Hartford, Connecticut. It does serve a few buildings in that city.

[Core_d]

The motors take 4 wires? Ph1,2,n,grand???

[Bazooka Joe]

" they may use a four wire delta connection to supply both 120:240 Volt single phase loads and 240 volt three phase loads."

Maybe that's what those units where? The 240 volt three phase for the compressor and for the blower motor and outdoor fan motor it was the 120 volt single phase ?


On a side note:

" Years ago large air conditioners were not available in single phase. Large homes in the south could have a four wire delta service fed from such an arrangement to power large air conditioners.
The 208 Volts to neutral on the third phase is called the wild leg or the high leg."

[rsmith46]

Its actually 3ph 240v power, but it only uses 2 transformers. The middle B phase is grounded so you have 240v from A and C phase's to ground but no voltage reading from B phase to ground, it will read 240v between any 2 conductors but no 120v available. Doesn't seem like it would work but it does.

[rsmith46]

"

" Years ago large air conditioners were not available in single phase. Large homes in the south could have a four wire delta service fed from such an arrangement to power large air conditioners.
The 208 Volts to neutral on the third phase is called the wild leg or the high leg."

Different type of 3 phase than what the OP ran into, but your right what your referring to is a wild leg 3ph. 2 legs read 120v to ground but 3rd leg reads 208v to ground. You get 208v between any 2 feed conductors. Here in KC we have four types of 3 phase, 240v delta, - 240v grounded B phase delta (what used to be called 2 phase, - no usable 120v on either types of 240v delta's.
Also standard 120v - 208v Wye that is most common, and the 120v - 208v wild leg Wye configuration your talking about. ( I have burnt out 2 vacuum pumps by hooking them up to the 208v to ground wild leg.

I'm an old Master Electrician and my dad was a KCP&L lineman for 40 years and I still don't fully understand the 4 different types of 3 phase power we have here.

[d2305]

https://en.wikipedia.org/wiki/Two-phase_electric_power. Good luck in finding 2 phase equipment.

[timebuilder]

2 phase power requires four power conductors and a grounding conductor.

It is still produced from the generated 3 phase for Center City Philadelphia using Scott-T transformer arrays, for feeders that run mostly along Walnut Street.

So if those rooftop units were 2 phase, each one would have four conductors and a ground going to it.

[COOLJIM]

Yes me to lost a recovery machine to a wild leg , on a compressor change out , make sure to check in future the voltage of phase to ground before using my cheater cord.

[Poodle Head Mikey]

What is the two-phase power used for these days?

PHM
-------

2 phase power requires four power conductors and a grounding conductor.

It is still produced from the generated 3 phase for Center City Philadelphia using Scott-T transformer arrays, for feeders that run mostly along Walnut Street.

So if those rooftop units were 2 phase, each one would have four conductors and a ground going to it.

[timebuilder]

What is the two-phase power used for these days?

PHM
-------

There are two answers.

The first answer is that newly remodeled stores with new panels will get their own Scott-T transformer to produce a three phase source to run RTU's and such.

The other use is to power an existing 2-phase power panel, where each phase pair is a 240 volt feed that can power 240 volt loads. There are very likely some old elevators that run on the 2-phase.

Mostly, the feeds power a transformer. I think all of the motor-generator sets are gone, but I could be wrong.

This is done to avoid having to pay for a new 3-phase conductor set to be brought in from the street. With permits and excavation costs, that be well in excess of $10 - 15k, and most of the corporates that rent store spaces along Walnut will do anything to avoid a complete service replacement. On top of that figure, there are metering cabinets and CT transformers that can raise the cost to $20k.