3 Phase Resi?

[kwired]

Keep in mind that these are normal single fam dwells in the heart of dwntwn phoenix, not exactly "farms" just fyi. So its still odd, even if only a few families on the street had livestock...i think in this part of town it was incubators, heaters and fans. Ill dig a bit deeper and see what i can find. Alot of homes still have a delta service.

Possible air conditioners were more common at one time in Phoenix than in many other areas of the nation? Of course I don't think they had the population at that time like they have now either but maybe was still more common to see air conditioners in dwellings there before many other areas? And three phase may been more common for over certain size than is now?

 

[kwired]

It depends on where you take your measurement. For a high leg service when you measure the voltage of the A and C phases relative to the center tap neutral, they are120V 180 degrees apart.

and the high leg is 90 degrees from the neutral conductor.

all three phase conductors are 120 degrees apart from the true neutral point although there is no conductor attached to that point.

 

[winnie]

and the high leg is 90 degrees from the neutral conductor.

all three phase conductors are 120 degrees apart from the true neutral point although there is no conductor attached to that point.

Exactly!

Phase angles are always relative to the reference point you select. In most systems there is one obvious reference point to use, and when we use that reference point we get the phase angles we expect.

But 'high leg delta' and a 'delta breaker' are head stretching because they are a hybrid of two systems, each with its own obvious reference point, and if you don't recognize that the reference point is changing you get seemingly incorrect phase angle numbers.

The obvious reference point to use for a split single phase system is the grounded neutral. Relative to this grounded neutral the two single phase 'hot' conductors are 180 degrees apart.

The obvious reference point for a three phase system is the three phase neutral (which isn't even present in a delta system), and the three 'hot' conductors are 120 degrees apart with respect to that reference point (and each other).

Not only is the 'true neutral point' that kwired described not physically present in the systems being described, it is at elevated voltage (about 68V) relative to the grounded single phase neutral that is actually present. If any of the three phase loads (say a star connected motor) derived this neutral, it would not be near zero voltage as in the case with a grounded wye three phase system.

-Jon

 

[kwired]

Exactly!

Phase angles are always relative to the reference point you select. In most systems there is one obvious reference point to use, and when we use that reference point we get the phase angles we expect.

But 'high leg delta' and a 'delta breaker' are head stretching because they are a hybrid of two systems, each with its own obvious reference point, and if you don't recognize that the reference point is changing you get seemingly incorrect phase angle numbers.

The obvious reference point to use for a split single phase system is the grounded neutral. Relative to this grounded neutral the two single phase 'hot' conductors are 180 degrees apart.

The obvious reference point for a three phase system is the three phase neutral (which isn't even present in a delta system), and the three 'hot' conductors are 120 degrees apart with respect to that reference point (and each other).

Not only is the 'true neutral point' that kwired described not physically present in the systems being described, it is at elevated voltage (about 68V) relative to the grounded single phase neutral that is actually present. If any of the three phase loads (say a star connected motor) derived this neutral, it would not be near zero voltage as in the case with a grounded wye three phase system.

-Jon

That "neutral" term is what causes some confusion.

As said a delta system has no conductor attached to the true neutral point. NEC sort of made this confusion worse when they decided to call the grounded midpoint of one phase "neutral", sometime in past 15 years I believe is when they did this. IMO they should just continue to refer to it as a grounded conductor only and not attach that neutral name to it. It is only neutral to the one side of the delta.

 

[ggunn]

That "neutral" term is what causes some confusion.

As said a delta system has no conductor attached to the true neutral point. NEC sort of made this confusion worse when they decided to call the grounded midpoint of one phase "neutral", sometime in past 15 years I believe is when they did this. IMO they should just continue to refer to it as a grounded conductor only and not attach that neutral name to it. It is only neutral to the one side of the delta.

Well, to someone who is using the A and C phases for single phase, the grounded conductor is indistinguishable from the neutral in a native single phase service.

 

[kwired]

Well, to someone who is using the A and C phases for single phase, the grounded conductor is indistinguishable from the neutral in a native single phase service.

I have no issue with calling that the neutral if you are only supplied with single phase service even though it comes off a delta arrangement. It is the neutral point of what is available to you.

It is not the true neutral of the three phase system though.

 

[ggunn]

I have no issue with calling that the neutral if you are only supplied with single phase service even though it comes off a delta arrangement. It is the neutral point of what is available to you.

It is not the true neutral of the three phase system though.

Of course, but to someone who is just using the A and C phases for single phase loads it's a distinction without a difference.

 

[Benderofmiami]

I haven't heard this question in a long time but I think I am right in saying that most power companies will not supply 3 phase power to a residence. Am I correct on this?

If you are willing to pay for it the utility will do it ,I did one along time ago ,they needed it for the chillers on the chilled water system ,pretty crazy
pretty sure it wasn't very cost effective it was 120/240 volt 3-phase,all the air handlers were 1-phase ,whoever sold them this
package could sell ice cubes to eskimos..

 

[Hv&Lv]

The center tap winding of a three phase delta system is the same as a single phase so line A to line B to line C are still 120 degrees apart.

here’s the open delta metering phasor:
The voltages aren’t 120 apart, but the currents are.
Rotation will determine if the center voltage is 270 or 90

 

[kwired]

If you are willing to pay for it the utility will do it ,I did one along time ago ,they needed it for the chillers on the chilled water system ,pretty crazy
pretty sure it wasn't very cost effective it was 120/240 volt 3-phase,all the air handlers were 1-phase ,whoever sold them this
package could sell ice cubes to eskimos..

Chillers apparently have a point where they are cost effective or else we wouldn't see them at all.

The 3 phase likely only needed for the chiller section. Probably not too common to see these units in small enough size that single phase compressors are much of an option, so sort of comes down to whether the unit was overkill for the cooling demand. If not it possibly was high efficiency but maybe at same time a high investment cost.

 

[hillbilly1]

I had a customer that wanted three phase for his house in the Caymen’s. Someone was trying to sell him a three phase desalinator. The salt water kept killing his grass, so he was going to use it to water his lawn!