Residential 3-phase power
- Thread starter chuckd83
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- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
The three phase motor produces effectively constant torque through each rotation, potentially reducing wear and tear on bearings and driven components. Less vibration. (That would be the more reliable part.)
There may also be a better power factor and certainly lower ampacity supply conductors (but more of them) needed than for single phase.
Would the starting surge necessarily be lower, or just provide better starting torque?
keep in mind I am speaking of motor (compressor) efficiency.
Here's an article from another website that discussed the matter:
http://www.practicalmachinist.com/v...d/3-phase-vs-1-phase-motor-efficiency-171972/
Here's an article from another website that discussed the matter:
http://www.practicalmachinist.com/v...d/3-phase-vs-1-phase-motor-efficiency-171972/
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Efficiency cannot be assumed, only measured (or determined from something that someone else measured). So if you look at a single phase motor that says it is 85% efficient, and a 3 phase motor that says it is 85% efficient, there is no difference. Watts are watts are watts. The delivery of MECHANICAL power to the motor is smoother for a 3 phase motor, and that will theoretically translate to longer equipment life, but if the equipment life is 25 years vs 28 years, are you going to notice?
What you might find with a 3 phase service however, is a nasty little surprise at the end of the month called a "Demand Charge" and/or a Power Factor penalty. Single phase residential services do not have these things, 3 phase usually do. So efficiency be damned, you may end up PAYING more just because you have a 3 phase service, whether or not you actually use it.
What you might find with a 3 phase service however, is a nasty little surprise at the end of the month called a "Demand Charge" and/or a Power Factor penalty. Single phase residential services do not have these things, 3 phase usually do. So efficiency be damned, you may end up PAYING more just because you have a 3 phase service, whether or not you actually use it.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Plus monthly minimum charges are usually higher for three phase - more equipment/more expensive equipment for distribution to provide/maintain, energy used is usually at the same rate for either source type.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Unless we are talking a large unit where you may have no choice but three phase, the three phase unit likely costs more than same sized unit in single phase, probably has similar efficiency and similar expected life - so probably the single phase unit.
Load balancing and overall electrical system performance or needs also need some consideration though. Most single family dwellings, other than big mansions, this is not much of an issue though.
mgookin
Senior Member
- Location
- Fort Myers, FL
- Occupation
- Retired inspector, plans examiner & building official
I'd do the single phase. Try calling a service company saying you need someone to service your 3 phase residential a/c system and those people are going to fall over confused. Single phase offers off the shelf everything.
Unless you are in an industrial/commercial area it would be highly unlikely that you would even have 3ph available at all.
Then, consider how many devices that you would have in a home that would benefit from 3ph. A 3 pH motor is extremely simple when compared to a 1ph motor but the HP that is require in a residence may make 3ph impractical.
Then, you would have to choose between a 208y/120 3ph4w and a 240d/120 3ph4w. 208v 1ph appliances are not as common as 240v.
Unless you have a very serious wood or machine shop on the premises where you may be if it from 3 pH power it is of my opinion that having a 3ph service may more for ego than practical.
Then, consider how many devices that you would have in a home that would benefit from 3ph. A 3 pH motor is extremely simple when compared to a 1ph motor but the HP that is require in a residence may make 3ph impractical.
Then, you would have to choose between a 208y/120 3ph4w and a 240d/120 3ph4w. 208v 1ph appliances are not as common as 240v.
Unless you have a very serious wood or machine shop on the premises where you may be if it from 3 pH power it is of my opinion that having a 3ph service may more for ego than practical.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
That wouldn't bother me, as the electrical problems that may come up, I would be the one servicing it, refrigeration servicing is the same either way.
OP said three phase is already available so the why is kind of a mute point.
I believe service is needed for the transformer feeding my house. I currently have a 3-phase condenser, but it needs replacing. If I go with a 1-phase, then call out the utility to look at the transformer and they find no 3-phase equipment at my house, will they switch it to 1-phase?
I want to keep the 3-phase service for a 'just in case' moment (maybe I get into wood working) and wondering what the utility will do. Maybe I'll call them out before replacing.
I want to keep the 3-phase service for a 'just in case' moment (maybe I get into wood working) and wondering what the utility will do. Maybe I'll call them out before replacing.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
131030-1055 EDT
chuckd83:
In my residential area there is primary 3 phase with no neutral, so you could call it a delta source. At my son's commericial building there is a 3 phase Y with only 2 phases and neutral brought to the pole where there are two transformers providing 3 phase open delta with a wild leg. Neither of these locations have demand billing. In my neighborhood I have at least two neighbors with 3 phase in their homes. These are two transformer open deltas with a wild leg.
Newer subdivisions have a 3 phase Y source for the primary with only one hot and neutral brought to regions, and therefore only single phase available.
There are a lot of secondary deltas with a wild leg in our area, primarily in commericial areas.
Why do you think you have a transformer problem? What are your voltage measurements to earth (stick a 12" screwdriver in the earth to measure as a reference)? Also what is your neutral to earth measurement?
.
chuckd83:
In my residential area there is primary 3 phase with no neutral, so you could call it a delta source. At my son's commericial building there is a 3 phase Y with only 2 phases and neutral brought to the pole where there are two transformers providing 3 phase open delta with a wild leg. Neither of these locations have demand billing. In my neighborhood I have at least two neighbors with 3 phase in their homes. These are two transformer open deltas with a wild leg.
Newer subdivisions have a 3 phase Y source for the primary with only one hot and neutral brought to regions, and therefore only single phase available.
There are a lot of secondary deltas with a wild leg in our area, primarily in commericial areas.
Why do you think you have a transformer problem? What are your voltage measurements to earth (stick a 12" screwdriver in the earth to measure as a reference)? Also what is your neutral to earth measurement?
.
It's not a voltage problem (I'll post the voltages tonight though), but there's a cable dangling around up on the pole. I'm not familiar with components, but it looks like it came off a surge arrester. And the transformer itself is old and rusty. Just wanted to get a feel of what the utility would do IF they replace it.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
You do not have to have three phase loads to utilize a three phase source.
Just having the third phase gives you 1.73 times more capacity if you keep the voltage and current levels the same.
A 200 amp 240 volt three phase system can deliver most of the KVA that a 400 amp 240 volt single phase system can,about 87%, but the problem is to get 240 volts three phase you either have a delta with a high leg, or 138 volts to ground if it is a wye system, so if there is significant 120 volt loads 208/120 wye is more desirable but with 200 amp gear and conductors total KVA available is about 75% of what it would be for 400 amps 240 single phase.
The advantage may be that the smaller gear and conductors cost less than the larger gear and conductors necessary to deliver the same KVA via single phase. 200 and 400 amp level may not be all that much cost difference but start increasing the needed KVA and it does start to make a difference. The more load you have the more interested the POCO becomes in balancing it across all three phases, even if none of the individual loads are actual three phase loads.
Just having the third phase gives you 1.73 times more capacity if you keep the voltage and current levels the same.
A 200 amp 240 volt three phase system can deliver most of the KVA that a 400 amp 240 volt single phase system can,about 87%, but the problem is to get 240 volts three phase you either have a delta with a high leg, or 138 volts to ground if it is a wye system, so if there is significant 120 volt loads 208/120 wye is more desirable but with 200 amp gear and conductors total KVA available is about 75% of what it would be for 400 amps 240 single phase.
The advantage may be that the smaller gear and conductors cost less than the larger gear and conductors necessary to deliver the same KVA via single phase. 200 and 400 amp level may not be all that much cost difference but start increasing the needed KVA and it does start to make a difference. The more load you have the more interested the POCO becomes in balancing it across all three phases, even if none of the individual loads are actual three phase loads.
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